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WSL2-Linux-Kernel/net/ipv4/tcp_input.c

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// SPDX-License-Identifier: GPL-2.0
/*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* Implementation of the Transmission Control Protocol(TCP).
*
* Authors: Ross Biro
* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
* Mark Evans, <evansmp@uhura.aston.ac.uk>
* Corey Minyard <wf-rch!minyard@relay.EU.net>
* Florian La Roche, <flla@stud.uni-sb.de>
* Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
* Linus Torvalds, <torvalds@cs.helsinki.fi>
* Alan Cox, <gw4pts@gw4pts.ampr.org>
* Matthew Dillon, <dillon@apollo.west.oic.com>
* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
* Jorge Cwik, <jorge@laser.satlink.net>
*/
/*
* Changes:
* Pedro Roque : Fast Retransmit/Recovery.
* Two receive queues.
* Retransmit queue handled by TCP.
* Better retransmit timer handling.
* New congestion avoidance.
* Header prediction.
* Variable renaming.
*
* Eric : Fast Retransmit.
* Randy Scott : MSS option defines.
* Eric Schenk : Fixes to slow start algorithm.
* Eric Schenk : Yet another double ACK bug.
* Eric Schenk : Delayed ACK bug fixes.
* Eric Schenk : Floyd style fast retrans war avoidance.
* David S. Miller : Don't allow zero congestion window.
* Eric Schenk : Fix retransmitter so that it sends
* next packet on ack of previous packet.
* Andi Kleen : Moved open_request checking here
* and process RSTs for open_requests.
* Andi Kleen : Better prune_queue, and other fixes.
* Andrey Savochkin: Fix RTT measurements in the presence of
* timestamps.
* Andrey Savochkin: Check sequence numbers correctly when
* removing SACKs due to in sequence incoming
* data segments.
* Andi Kleen: Make sure we never ack data there is not
* enough room for. Also make this condition
* a fatal error if it might still happen.
* Andi Kleen: Add tcp_measure_rcv_mss to make
* connections with MSS<min(MTU,ann. MSS)
* work without delayed acks.
* Andi Kleen: Process packets with PSH set in the
* fast path.
* J Hadi Salim: ECN support
* Andrei Gurtov,
* Pasi Sarolahti,
* Panu Kuhlberg: Experimental audit of TCP (re)transmission
* engine. Lots of bugs are found.
* Pasi Sarolahti: F-RTO for dealing with spurious RTOs
*/
#define pr_fmt(fmt) "TCP: " fmt
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/kernel.h>
#include <linux/prefetch.h>
#include <net/dst.h>
#include <net/tcp.h>
#include <net/inet_common.h>
#include <linux/ipsec.h>
#include <asm/unaligned.h>
#include <linux/errqueue.h>
#include <trace/events/tcp.h>
#include <linux/jump_label_ratelimit.h>
#include <net/busy_poll.h>
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
#define FLAG_DATA 0x01 /* Incoming frame contained data. */
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
#define FLAG_DATA_SACKED 0x20 /* New SACK. */
#define FLAG_ECE 0x40 /* ECE in this ACK */
#define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
#define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
#define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */
#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
#define REXMIT_NONE 0 /* no loss recovery to do */
#define REXMIT_LOST 1 /* retransmit packets marked lost */
#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
#if IS_ENABLED(CONFIG_TLS_DEVICE)
static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
void clean_acked_data_enable(struct inet_connection_sock *icsk,
void (*cad)(struct sock *sk, u32 ack_seq))
{
icsk->icsk_clean_acked = cad;
static_branch_inc(&clean_acked_data_enabled.key);
}
EXPORT_SYMBOL_GPL(clean_acked_data_enable);
void clean_acked_data_disable(struct inet_connection_sock *icsk)
{
static_branch_slow_dec_deferred(&clean_acked_data_enabled);
icsk->icsk_clean_acked = NULL;
}
EXPORT_SYMBOL_GPL(clean_acked_data_disable);
void clean_acked_data_flush(void)
{
static_key_deferred_flush(&clean_acked_data_enabled);
}
EXPORT_SYMBOL_GPL(clean_acked_data_flush);
#endif
static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
unsigned int len)
{
static bool __once __read_mostly;
if (!__once) {
struct net_device *dev;
__once = true;
rcu_read_lock();
dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
if (!dev || len >= dev->mtu)
pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
dev ? dev->name : "Unknown driver");
rcu_read_unlock();
}
}
/* Adapt the MSS value used to make delayed ack decision to the
* real world.
*/
static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const unsigned int lss = icsk->icsk_ack.last_seg_size;
unsigned int len;
icsk->icsk_ack.last_seg_size = 0;
/* skb->len may jitter because of SACKs, even if peer
* sends good full-sized frames.
*/
len = skb_shinfo(skb)->gso_size ? : skb->len;
if (len >= icsk->icsk_ack.rcv_mss) {
icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
tcp_sk(sk)->advmss);
/* Account for possibly-removed options */
if (unlikely(len > icsk->icsk_ack.rcv_mss +
MAX_TCP_OPTION_SPACE))
tcp_gro_dev_warn(sk, skb, len);
} else {
/* Otherwise, we make more careful check taking into account,
* that SACKs block is variable.
*
* "len" is invariant segment length, including TCP header.
*/
len += skb->data - skb_transport_header(skb);
if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
/* If PSH is not set, packet should be
* full sized, provided peer TCP is not badly broken.
* This observation (if it is correct 8)) allows
* to handle super-low mtu links fairly.
*/
(len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
!(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
/* Subtract also invariant (if peer is RFC compliant),
* tcp header plus fixed timestamp option length.
* Resulting "len" is MSS free of SACK jitter.
*/
len -= tcp_sk(sk)->tcp_header_len;
icsk->icsk_ack.last_seg_size = len;
if (len == lss) {
icsk->icsk_ack.rcv_mss = len;
return;
}
}
if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
}
}
static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
{
struct inet_connection_sock *icsk = inet_csk(sk);
unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
if (quickacks == 0)
quickacks = 2;
quickacks = min(quickacks, max_quickacks);
if (quickacks > icsk->icsk_ack.quick)
icsk->icsk_ack.quick = quickacks;
}
void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
{
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_incr_quickack(sk, max_quickacks);
inet_csk_exit_pingpong_mode(sk);
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
EXPORT_SYMBOL(tcp_enter_quickack_mode);
/* Send ACKs quickly, if "quick" count is not exhausted
* and the session is not interactive.
*/
static bool tcp_in_quickack_mode(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct dst_entry *dst = __sk_dst_get(sk);
return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
}
static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
{
if (tp->ecn_flags & TCP_ECN_OK)
tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
}
static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
{
if (tcp_hdr(skb)->cwr) {
tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
/* If the sender is telling us it has entered CWR, then its
* cwnd may be very low (even just 1 packet), so we should ACK
* immediately.
*/
inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
}
}
static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
{
tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
}
static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
case INET_ECN_NOT_ECT:
/* Funny extension: if ECT is not set on a segment,
* and we already seen ECT on a previous segment,
* it is probably a retransmit.
*/
if (tp->ecn_flags & TCP_ECN_SEEN)
tcp_enter_quickack_mode(sk, 2);
break;
case INET_ECN_CE:
if (tcp_ca_needs_ecn(sk))
tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
/* Better not delay acks, sender can have a very low cwnd */
tcp_enter_quickack_mode(sk, 2);
tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
}
tp->ecn_flags |= TCP_ECN_SEEN;
break;
default:
if (tcp_ca_needs_ecn(sk))
tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
tp->ecn_flags |= TCP_ECN_SEEN;
break;
}
}
static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
{
if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
__tcp_ecn_check_ce(sk, skb);
}
static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
{
if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
tp->ecn_flags &= ~TCP_ECN_OK;
}
static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
{
if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
tp->ecn_flags &= ~TCP_ECN_OK;
}
static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
{
if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
return true;
return false;
}
/* Buffer size and advertised window tuning.
*
* 1. Tuning sk->sk_sndbuf, when connection enters established state.
*/
static void tcp_sndbuf_expand(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
int sndmem, per_mss;
u32 nr_segs;
/* Worst case is non GSO/TSO : each frame consumes one skb
* and skb->head is kmalloced using power of two area of memory
*/
per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
MAX_TCP_HEADER +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
per_mss = roundup_pow_of_two(per_mss) +
SKB_DATA_ALIGN(sizeof(struct sk_buff));
nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
/* Fast Recovery (RFC 5681 3.2) :
* Cubic needs 1.7 factor, rounded to 2 to include
* extra cushion (application might react slowly to EPOLLOUT)
*/
sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
sndmem *= nr_segs * per_mss;
if (sk->sk_sndbuf < sndmem)
sk->sk_sndbuf = min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]);
}
/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
*
* All tcp_full_space() is split to two parts: "network" buffer, allocated
* forward and advertised in receiver window (tp->rcv_wnd) and
* "application buffer", required to isolate scheduling/application
* latencies from network.
* window_clamp is maximal advertised window. It can be less than
* tcp_full_space(), in this case tcp_full_space() - window_clamp
* is reserved for "application" buffer. The less window_clamp is
* the smoother our behaviour from viewpoint of network, but the lower
* throughput and the higher sensitivity of the connection to losses. 8)
*
* rcv_ssthresh is more strict window_clamp used at "slow start"
* phase to predict further behaviour of this connection.
* It is used for two goals:
* - to enforce header prediction at sender, even when application
* requires some significant "application buffer". It is check #1.
* - to prevent pruning of receive queue because of misprediction
* of receiver window. Check #2.
*
* The scheme does not work when sender sends good segments opening
* window and then starts to feed us spaghetti. But it should work
* in common situations. Otherwise, we have to rely on queue collapsing.
*/
/* Slow part of check#2. */
static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Optimize this! */
int truesize = tcp_win_from_space(sk, skb->truesize) >> 1;
int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
while (tp->rcv_ssthresh <= window) {
if (truesize <= skb->len)
return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
truesize >>= 1;
window >>= 1;
}
return 0;
}
static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
int room;
room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
/* Check #1 */
if (room > 0 && !tcp_under_memory_pressure(sk)) {
int incr;
/* Check #2. Increase window, if skb with such overhead
* will fit to rcvbuf in future.
*/
if (tcp_win_from_space(sk, skb->truesize) <= skb->len)
incr = 2 * tp->advmss;
else
incr = __tcp_grow_window(sk, skb);
if (incr) {
incr = max_t(int, incr, 2 * skb->len);
tp->rcv_ssthresh += min(room, incr);
inet_csk(sk)->icsk_ack.quick |= 1;
}
}
}
/* 3. Try to fixup all. It is made immediately after connection enters
* established state.
*/
void tcp_init_buffer_space(struct sock *sk)
{
int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
struct tcp_sock *tp = tcp_sk(sk);
int maxwin;
if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
tcp_sndbuf_expand(sk);
tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss);
tcp_mstamp_refresh(tp);
tp->rcvq_space.time = tp->tcp_mstamp;
tp->rcvq_space.seq = tp->copied_seq;
maxwin = tcp_full_space(sk);
if (tp->window_clamp >= maxwin) {
tp->window_clamp = maxwin;
if (tcp_app_win && maxwin > 4 * tp->advmss)
tp->window_clamp = max(maxwin -
(maxwin >> tcp_app_win),
4 * tp->advmss);
}
/* Force reservation of one segment. */
if (tcp_app_win &&
tp->window_clamp > 2 * tp->advmss &&
tp->window_clamp + tp->advmss > maxwin)
tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
tp->snd_cwnd_stamp = tcp_jiffies32;
}
/* 4. Recalculate window clamp after socket hit its memory bounds. */
static void tcp_clamp_window(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
struct net *net = sock_net(sk);
icsk->icsk_ack.quick = 0;
if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
!tcp_under_memory_pressure(sk) &&
sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
net->ipv4.sysctl_tcp_rmem[2]);
}
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
}
/* Initialize RCV_MSS value.
* RCV_MSS is an our guess about MSS used by the peer.
* We haven't any direct information about the MSS.
* It's better to underestimate the RCV_MSS rather than overestimate.
* Overestimations make us ACKing less frequently than needed.
* Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
*/
void tcp_initialize_rcv_mss(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
hint = min(hint, tp->rcv_wnd / 2);
hint = min(hint, TCP_MSS_DEFAULT);
hint = max(hint, TCP_MIN_MSS);
inet_csk(sk)->icsk_ack.rcv_mss = hint;
}
EXPORT_SYMBOL(tcp_initialize_rcv_mss);
/* Receiver "autotuning" code.
*
* The algorithm for RTT estimation w/o timestamps is based on
* Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
* <http://public.lanl.gov/radiant/pubs.html#DRS>
*
* More detail on this code can be found at
* <http://staff.psc.edu/jheffner/>,
* though this reference is out of date. A new paper
* is pending.
*/
static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
{
u32 new_sample = tp->rcv_rtt_est.rtt_us;
long m = sample;
if (new_sample != 0) {
/* If we sample in larger samples in the non-timestamp
* case, we could grossly overestimate the RTT especially
* with chatty applications or bulk transfer apps which
* are stalled on filesystem I/O.
*
* Also, since we are only going for a minimum in the
* non-timestamp case, we do not smooth things out
* else with timestamps disabled convergence takes too
* long.
*/
if (!win_dep) {
m -= (new_sample >> 3);
new_sample += m;
} else {
m <<= 3;
if (m < new_sample)
new_sample = m;
}
} else {
/* No previous measure. */
new_sample = m << 3;
}
tp->rcv_rtt_est.rtt_us = new_sample;
}
static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
{
u32 delta_us;
if (tp->rcv_rtt_est.time == 0)
goto new_measure;
if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
return;
delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
if (!delta_us)
delta_us = 1;
tcp_rcv_rtt_update(tp, delta_us, 1);
new_measure:
tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
tp->rcv_rtt_est.time = tp->tcp_mstamp;
}
static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
return;
tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
if (TCP_SKB_CB(skb)->end_seq -
TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
u32 delta_us;
if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
if (!delta)
delta = 1;
delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
tcp_rcv_rtt_update(tp, delta_us, 0);
}
}
}
/*
* This function should be called every time data is copied to user space.
* It calculates the appropriate TCP receive buffer space.
*/
void tcp_rcv_space_adjust(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 copied;
int time;
trace_tcp_rcv_space_adjust(sk);
tcp_mstamp_refresh(tp);
time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
return;
/* Number of bytes copied to user in last RTT */
copied = tp->copied_seq - tp->rcvq_space.seq;
if (copied <= tp->rcvq_space.space)
goto new_measure;
/* A bit of theory :
* copied = bytes received in previous RTT, our base window
* To cope with packet losses, we need a 2x factor
* To cope with slow start, and sender growing its cwin by 100 %
* every RTT, we need a 4x factor, because the ACK we are sending
* now is for the next RTT, not the current one :
* <prev RTT . ><current RTT .. ><next RTT .... >
*/
if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
int rcvmem, rcvbuf;
u64 rcvwin, grow;
/* minimal window to cope with packet losses, assuming
* steady state. Add some cushion because of small variations.
*/
rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
/* Accommodate for sender rate increase (eg. slow start) */
grow = rcvwin * (copied - tp->rcvq_space.space);
do_div(grow, tp->rcvq_space.space);
rcvwin += (grow << 1);
rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
rcvmem += 128;
do_div(rcvwin, tp->advmss);
rcvbuf = min_t(u64, rcvwin * rcvmem,
sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
if (rcvbuf > sk->sk_rcvbuf) {
sk->sk_rcvbuf = rcvbuf;
/* Make the window clamp follow along. */
tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
}
}
tp->rcvq_space.space = copied;
new_measure:
tp->rcvq_space.seq = tp->copied_seq;
tp->rcvq_space.time = tp->tcp_mstamp;
}
/* There is something which you must keep in mind when you analyze the
* behavior of the tp->ato delayed ack timeout interval. When a
* connection starts up, we want to ack as quickly as possible. The
* problem is that "good" TCP's do slow start at the beginning of data
* transmission. The means that until we send the first few ACK's the
* sender will sit on his end and only queue most of his data, because
* he can only send snd_cwnd unacked packets at any given time. For
* each ACK we send, he increments snd_cwnd and transmits more of his
* queue. -DaveM
*/
static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
u32 now;
inet_csk_schedule_ack(sk);
tcp_measure_rcv_mss(sk, skb);
tcp_rcv_rtt_measure(tp);
now = tcp_jiffies32;
if (!icsk->icsk_ack.ato) {
/* The _first_ data packet received, initialize
* delayed ACK engine.
*/
tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
icsk->icsk_ack.ato = TCP_ATO_MIN;
} else {
int m = now - icsk->icsk_ack.lrcvtime;
if (m <= TCP_ATO_MIN / 2) {
/* The fastest case is the first. */
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
} else if (m < icsk->icsk_ack.ato) {
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
if (icsk->icsk_ack.ato > icsk->icsk_rto)
icsk->icsk_ack.ato = icsk->icsk_rto;
} else if (m > icsk->icsk_rto) {
/* Too long gap. Apparently sender failed to
* restart window, so that we send ACKs quickly.
*/
tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
sk_mem_reclaim(sk);
}
}
icsk->icsk_ack.lrcvtime = now;
tcp_ecn_check_ce(sk, skb);
if (skb->len >= 128)
tcp_grow_window(sk, skb);
}
/* Called to compute a smoothed rtt estimate. The data fed to this
* routine either comes from timestamps, or from segments that were
* known _not_ to have been retransmitted [see Karn/Partridge
* Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
* piece by Van Jacobson.
* NOTE: the next three routines used to be one big routine.
* To save cycles in the RFC 1323 implementation it was better to break
* it up into three procedures. -- erics
*/
static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
{
struct tcp_sock *tp = tcp_sk(sk);
long m = mrtt_us; /* RTT */
u32 srtt = tp->srtt_us;
/* The following amusing code comes from Jacobson's
* article in SIGCOMM '88. Note that rtt and mdev
* are scaled versions of rtt and mean deviation.
* This is designed to be as fast as possible
* m stands for "measurement".
*
* On a 1990 paper the rto value is changed to:
* RTO = rtt + 4 * mdev
*
* Funny. This algorithm seems to be very broken.
* These formulae increase RTO, when it should be decreased, increase
* too slowly, when it should be increased quickly, decrease too quickly
* etc. I guess in BSD RTO takes ONE value, so that it is absolutely
* does not matter how to _calculate_ it. Seems, it was trap
* that VJ failed to avoid. 8)
*/
if (srtt != 0) {
m -= (srtt >> 3); /* m is now error in rtt est */
srtt += m; /* rtt = 7/8 rtt + 1/8 new */
if (m < 0) {
m = -m; /* m is now abs(error) */
m -= (tp->mdev_us >> 2); /* similar update on mdev */
/* This is similar to one of Eifel findings.
* Eifel blocks mdev updates when rtt decreases.
* This solution is a bit different: we use finer gain
* for mdev in this case (alpha*beta).
* Like Eifel it also prevents growth of rto,
* but also it limits too fast rto decreases,
* happening in pure Eifel.
*/
if (m > 0)
m >>= 3;
} else {
m -= (tp->mdev_us >> 2); /* similar update on mdev */
}
tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
if (tp->mdev_us > tp->mdev_max_us) {
tp->mdev_max_us = tp->mdev_us;
if (tp->mdev_max_us > tp->rttvar_us)
tp->rttvar_us = tp->mdev_max_us;
}
if (after(tp->snd_una, tp->rtt_seq)) {
if (tp->mdev_max_us < tp->rttvar_us)
tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
tp->rtt_seq = tp->snd_nxt;
tp->mdev_max_us = tcp_rto_min_us(sk);
}
} else {
/* no previous measure. */
srtt = m << 3; /* take the measured time to be rtt */
tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
tp->mdev_max_us = tp->rttvar_us;
tp->rtt_seq = tp->snd_nxt;
}
tp->srtt_us = max(1U, srtt);
}
static void tcp_update_pacing_rate(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
u64 rate;
/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
/* current rate is (cwnd * mss) / srtt
* In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
* In Congestion Avoidance phase, set it to 120 % the current rate.
*
* [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
* If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
* end of slow start and should slow down.
*/
if (tp->snd_cwnd < tp->snd_ssthresh / 2)
rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
else
rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
rate *= max(tp->snd_cwnd, tp->packets_out);
if (likely(tp->srtt_us))
do_div(rate, tp->srtt_us);
/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
* without any lock. We want to make sure compiler wont store
* intermediate values in this location.
*/
WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
sk->sk_max_pacing_rate));
}
/* Calculate rto without backoff. This is the second half of Van Jacobson's
* routine referred to above.
*/
static void tcp_set_rto(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Old crap is replaced with new one. 8)
*
* More seriously:
* 1. If rtt variance happened to be less 50msec, it is hallucination.
* It cannot be less due to utterly erratic ACK generation made
* at least by solaris and freebsd. "Erratic ACKs" has _nothing_
* to do with delayed acks, because at cwnd>2 true delack timeout
* is invisible. Actually, Linux-2.4 also generates erratic
* ACKs in some circumstances.
*/
inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
/* 2. Fixups made earlier cannot be right.
* If we do not estimate RTO correctly without them,
* all the algo is pure shit and should be replaced
* with correct one. It is exactly, which we pretend to do.
*/
/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
* guarantees that rto is higher.
*/
tcp_bound_rto(sk);
}
__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
{
__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
if (!cwnd)
cwnd = TCP_INIT_CWND;
return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
}
/* Take a notice that peer is sending D-SACKs */
static void tcp_dsack_seen(struct tcp_sock *tp)
{
tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
tp->rack.dsack_seen = 1;
tp->dsack_dups++;
}
/* It's reordering when higher sequence was delivered (i.e. sacked) before
* some lower never-retransmitted sequence ("low_seq"). The maximum reordering
* distance is approximated in full-mss packet distance ("reordering").
*/
static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
const int ts)
{
struct tcp_sock *tp = tcp_sk(sk);
const u32 mss = tp->mss_cache;
u32 fack, metric;
fack = tcp_highest_sack_seq(tp);
if (!before(low_seq, fack))
return;
metric = fack - low_seq;
if ((metric > tp->reordering * mss) && mss) {
#if FASTRETRANS_DEBUG > 1
pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
tp->reordering,
0,
tp->sacked_out,
tp->undo_marker ? tp->undo_retrans : 0);
#endif
tp->reordering = min_t(u32, (metric + mss - 1) / mss,
sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
}
/* This exciting event is worth to be remembered. 8) */
tp->reord_seen++;
NET_INC_STATS(sock_net(sk),
ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
}
/* This must be called before lost_out is incremented */
static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
{
if (!tp->retransmit_skb_hint ||
before(TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
tp->retransmit_skb_hint = skb;
}
/* Sum the number of packets on the wire we have marked as lost.
* There are two cases we care about here:
* a) Packet hasn't been marked lost (nor retransmitted),
* and this is the first loss.
* b) Packet has been marked both lost and retransmitted,
* and this means we think it was lost again.
*/
static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
__u8 sacked = TCP_SKB_CB(skb)->sacked;
if (!(sacked & TCPCB_LOST) ||
((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
tp->lost += tcp_skb_pcount(skb);
}
static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tcp_verify_retransmit_hint(tp, skb);
tp->lost_out += tcp_skb_pcount(skb);
tcp_sum_lost(tp, skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
}
}
void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
{
tcp_verify_retransmit_hint(tp, skb);
tcp_sum_lost(tp, skb);
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tp->lost_out += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
}
}
/* This procedure tags the retransmission queue when SACKs arrive.
*
* We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
* Packets in queue with these bits set are counted in variables
* sacked_out, retrans_out and lost_out, correspondingly.
*
* Valid combinations are:
* Tag InFlight Description
* 0 1 - orig segment is in flight.
* S 0 - nothing flies, orig reached receiver.
* L 0 - nothing flies, orig lost by net.
* R 2 - both orig and retransmit are in flight.
* L|R 1 - orig is lost, retransmit is in flight.
* S|R 1 - orig reached receiver, retrans is still in flight.
* (L|S|R is logically valid, it could occur when L|R is sacked,
* but it is equivalent to plain S and code short-curcuits it to S.
* L|S is logically invalid, it would mean -1 packet in flight 8))
*
* These 6 states form finite state machine, controlled by the following events:
* 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
* 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
* 3. Loss detection event of two flavors:
* A. Scoreboard estimator decided the packet is lost.
* A'. Reno "three dupacks" marks head of queue lost.
* B. SACK arrives sacking SND.NXT at the moment, when the
* segment was retransmitted.
* 4. D-SACK added new rule: D-SACK changes any tag to S.
*
* It is pleasant to note, that state diagram turns out to be commutative,
* so that we are allowed not to be bothered by order of our actions,
* when multiple events arrive simultaneously. (see the function below).
*
* Reordering detection.
* --------------------
* Reordering metric is maximal distance, which a packet can be displaced
* in packet stream. With SACKs we can estimate it:
*
* 1. SACK fills old hole and the corresponding segment was not
* ever retransmitted -> reordering. Alas, we cannot use it
* when segment was retransmitted.
* 2. The last flaw is solved with D-SACK. D-SACK arrives
* for retransmitted and already SACKed segment -> reordering..
* Both of these heuristics are not used in Loss state, when we cannot
* account for retransmits accurately.
*
* SACK block validation.
* ----------------------
*
* SACK block range validation checks that the received SACK block fits to
* the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
* Note that SND.UNA is not included to the range though being valid because
* it means that the receiver is rather inconsistent with itself reporting
* SACK reneging when it should advance SND.UNA. Such SACK block this is
* perfectly valid, however, in light of RFC2018 which explicitly states
* that "SACK block MUST reflect the newest segment. Even if the newest
* segment is going to be discarded ...", not that it looks very clever
* in case of head skb. Due to potentional receiver driven attacks, we
* choose to avoid immediate execution of a walk in write queue due to
* reneging and defer head skb's loss recovery to standard loss recovery
* procedure that will eventually trigger (nothing forbids us doing this).
*
* Implements also blockage to start_seq wrap-around. Problem lies in the
* fact that though start_seq (s) is before end_seq (i.e., not reversed),
* there's no guarantee that it will be before snd_nxt (n). The problem
* happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
* wrap (s_w):
*
* <- outs wnd -> <- wrapzone ->
* u e n u_w e_w s n_w
* | | | | | | |
* |<------------+------+----- TCP seqno space --------------+---------->|
* ...-- <2^31 ->| |<--------...
* ...---- >2^31 ------>| |<--------...
*
* Current code wouldn't be vulnerable but it's better still to discard such
* crazy SACK blocks. Doing this check for start_seq alone closes somewhat
* similar case (end_seq after snd_nxt wrap) as earlier reversed check in
* snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
* equal to the ideal case (infinite seqno space without wrap caused issues).
*
* With D-SACK the lower bound is extended to cover sequence space below
* SND.UNA down to undo_marker, which is the last point of interest. Yet
* again, D-SACK block must not to go across snd_una (for the same reason as
* for the normal SACK blocks, explained above). But there all simplicity
* ends, TCP might receive valid D-SACKs below that. As long as they reside
* fully below undo_marker they do not affect behavior in anyway and can
* therefore be safely ignored. In rare cases (which are more or less
* theoretical ones), the D-SACK will nicely cross that boundary due to skb
* fragmentation and packet reordering past skb's retransmission. To consider
* them correctly, the acceptable range must be extended even more though
* the exact amount is rather hard to quantify. However, tp->max_window can
* be used as an exaggerated estimate.
*/
static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
u32 start_seq, u32 end_seq)
{
/* Too far in future, or reversed (interpretation is ambiguous) */
if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
return false;
/* Nasty start_seq wrap-around check (see comments above) */
if (!before(start_seq, tp->snd_nxt))
return false;
/* In outstanding window? ...This is valid exit for D-SACKs too.
* start_seq == snd_una is non-sensical (see comments above)
*/
if (after(start_seq, tp->snd_una))
return true;
if (!is_dsack || !tp->undo_marker)
return false;
/* ...Then it's D-SACK, and must reside below snd_una completely */
if (after(end_seq, tp->snd_una))
return false;
if (!before(start_seq, tp->undo_marker))
return true;
/* Too old */
if (!after(end_seq, tp->undo_marker))
return false;
/* Undo_marker boundary crossing (overestimates a lot). Known already:
* start_seq < undo_marker and end_seq >= undo_marker.
*/
return !before(start_seq, end_seq - tp->max_window);
}
static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
struct tcp_sack_block_wire *sp, int num_sacks,
u32 prior_snd_una)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
bool dup_sack = false;
if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
dup_sack = true;
tcp_dsack_seen(tp);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
} else if (num_sacks > 1) {
u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
if (!after(end_seq_0, end_seq_1) &&
!before(start_seq_0, start_seq_1)) {
dup_sack = true;
tcp_dsack_seen(tp);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPDSACKOFORECV);
}
}
/* D-SACK for already forgotten data... Do dumb counting. */
if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
!after(end_seq_0, prior_snd_una) &&
after(end_seq_0, tp->undo_marker))
tp->undo_retrans--;
return dup_sack;
}
struct tcp_sacktag_state {
u32 reord;
/* Timestamps for earliest and latest never-retransmitted segment
* that was SACKed. RTO needs the earliest RTT to stay conservative,
* but congestion control should still get an accurate delay signal.
*/
u64 first_sackt;
u64 last_sackt;
struct rate_sample *rate;
int flag;
unsigned int mss_now;
};
/* Check if skb is fully within the SACK block. In presence of GSO skbs,
* the incoming SACK may not exactly match but we can find smaller MSS
* aligned portion of it that matches. Therefore we might need to fragment
* which may fail and creates some hassle (caller must handle error case
* returns).
*
* FIXME: this could be merged to shift decision code
*/
static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
u32 start_seq, u32 end_seq)
{
int err;
bool in_sack;
unsigned int pkt_len;
unsigned int mss;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
!before(end_seq, TCP_SKB_CB(skb)->end_seq);
if (tcp_skb_pcount(skb) > 1 && !in_sack &&
after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
mss = tcp_skb_mss(skb);
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
if (!in_sack) {
pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
if (pkt_len < mss)
pkt_len = mss;
} else {
pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
if (pkt_len < mss)
return -EINVAL;
}
/* Round if necessary so that SACKs cover only full MSSes
* and/or the remaining small portion (if present)
*/
if (pkt_len > mss) {
unsigned int new_len = (pkt_len / mss) * mss;
if (!in_sack && new_len < pkt_len)
new_len += mss;
pkt_len = new_len;
}
if (pkt_len >= skb->len && !in_sack)
return 0;
err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
pkt_len, mss, GFP_ATOMIC);
if (err < 0)
return err;
}
return in_sack;
}
/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
static u8 tcp_sacktag_one(struct sock *sk,
struct tcp_sacktag_state *state, u8 sacked,
u32 start_seq, u32 end_seq,
int dup_sack, int pcount,
u64 xmit_time)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Account D-SACK for retransmitted packet. */
if (dup_sack && (sacked & TCPCB_RETRANS)) {
if (tp->undo_marker && tp->undo_retrans > 0 &&
after(end_seq, tp->undo_marker))
tp->undo_retrans--;
if ((sacked & TCPCB_SACKED_ACKED) &&
before(start_seq, state->reord))
state->reord = start_seq;
}
/* Nothing to do; acked frame is about to be dropped (was ACKed). */
if (!after(end_seq, tp->snd_una))
return sacked;
if (!(sacked & TCPCB_SACKED_ACKED)) {
tcp_rack_advance(tp, sacked, end_seq, xmit_time);
if (sacked & TCPCB_SACKED_RETRANS) {
/* If the segment is not tagged as lost,
* we do not clear RETRANS, believing
* that retransmission is still in flight.
*/
if (sacked & TCPCB_LOST) {
sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
tp->lost_out -= pcount;
tp->retrans_out -= pcount;
}
} else {
if (!(sacked & TCPCB_RETRANS)) {
/* New sack for not retransmitted frame,
* which was in hole. It is reordering.
*/
if (before(start_seq,
tcp_highest_sack_seq(tp)) &&
before(start_seq, state->reord))
state->reord = start_seq;
if (!after(end_seq, tp->high_seq))
state->flag |= FLAG_ORIG_SACK_ACKED;
if (state->first_sackt == 0)
state->first_sackt = xmit_time;
state->last_sackt = xmit_time;
}
if (sacked & TCPCB_LOST) {
sacked &= ~TCPCB_LOST;
tp->lost_out -= pcount;
}
}
sacked |= TCPCB_SACKED_ACKED;
state->flag |= FLAG_DATA_SACKED;
tp->sacked_out += pcount;
tp->delivered += pcount; /* Out-of-order packets delivered */
/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
if (tp->lost_skb_hint &&
before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
tp->lost_cnt_hint += pcount;
}
/* D-SACK. We can detect redundant retransmission in S|R and plain R
* frames and clear it. undo_retrans is decreased above, L|R frames
* are accounted above as well.
*/
if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= pcount;
}
return sacked;
}
/* Shift newly-SACKed bytes from this skb to the immediately previous
* already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
*/
static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
struct sk_buff *skb,
struct tcp_sacktag_state *state,
unsigned int pcount, int shifted, int mss,
bool dup_sack)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
BUG_ON(!pcount);
/* Adjust counters and hints for the newly sacked sequence
* range but discard the return value since prev is already
* marked. We must tag the range first because the seq
* advancement below implicitly advances
* tcp_highest_sack_seq() when skb is highest_sack.
*/
tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
start_seq, end_seq, dup_sack, pcount,
tcp_skb_timestamp_us(skb));
tcp_rate_skb_delivered(sk, skb, state->rate);
if (skb == tp->lost_skb_hint)
tp->lost_cnt_hint += pcount;
TCP_SKB_CB(prev)->end_seq += shifted;
TCP_SKB_CB(skb)->seq += shifted;
tcp_skb_pcount_add(prev, pcount);
BUG_ON(tcp_skb_pcount(skb) < pcount);
tcp_skb_pcount_add(skb, -pcount);
/* When we're adding to gso_segs == 1, gso_size will be zero,
* in theory this shouldn't be necessary but as long as DSACK
* code can come after this skb later on it's better to keep
* setting gso_size to something.
*/
if (!TCP_SKB_CB(prev)->tcp_gso_size)
TCP_SKB_CB(prev)->tcp_gso_size = mss;
/* CHECKME: To clear or not to clear? Mimics normal skb currently */
if (tcp_skb_pcount(skb) <= 1)
TCP_SKB_CB(skb)->tcp_gso_size = 0;
/* Difference in this won't matter, both ACKed by the same cumul. ACK */
TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
if (skb->len > 0) {
BUG_ON(!tcp_skb_pcount(skb));
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
return false;
}
/* Whole SKB was eaten :-) */
if (skb == tp->retransmit_skb_hint)
tp->retransmit_skb_hint = prev;
if (skb == tp->lost_skb_hint) {
tp->lost_skb_hint = prev;
tp->lost_cnt_hint -= tcp_skb_pcount(prev);
}
TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
TCP_SKB_CB(prev)->end_seq++;
if (skb == tcp_highest_sack(sk))
tcp_advance_highest_sack(sk, skb);
tcp_skb_collapse_tstamp(prev, skb);
if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
tcp_rtx_queue_unlink_and_free(skb, sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
return true;
}
/* I wish gso_size would have a bit more sane initialization than
* something-or-zero which complicates things
*/
static int tcp_skb_seglen(const struct sk_buff *skb)
{
return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
}
/* Shifting pages past head area doesn't work */
static int skb_can_shift(const struct sk_buff *skb)
{
return !skb_headlen(skb) && skb_is_nonlinear(skb);
}
/* Try collapsing SACK blocks spanning across multiple skbs to a single
* skb.
*/
static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
struct tcp_sacktag_state *state,
u32 start_seq, u32 end_seq,
bool dup_sack)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *prev;
int mss;
int pcount = 0;
int len;
int in_sack;
/* Normally R but no L won't result in plain S */
if (!dup_sack &&
(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
goto fallback;
if (!skb_can_shift(skb))
goto fallback;
/* This frame is about to be dropped (was ACKed). */
if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
goto fallback;
/* Can only happen with delayed DSACK + discard craziness */
prev = skb_rb_prev(skb);
if (!prev)
goto fallback;
if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
goto fallback;
if (!tcp_skb_can_collapse_to(prev))
goto fallback;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
!before(end_seq, TCP_SKB_CB(skb)->end_seq);
if (in_sack) {
len = skb->len;
pcount = tcp_skb_pcount(skb);
mss = tcp_skb_seglen(skb);
/* TODO: Fix DSACKs to not fragment already SACKed and we can
* drop this restriction as unnecessary
*/
if (mss != tcp_skb_seglen(prev))
goto fallback;
} else {
if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
goto noop;
/* CHECKME: This is non-MSS split case only?, this will
* cause skipped skbs due to advancing loop btw, original
* has that feature too
*/
if (tcp_skb_pcount(skb) <= 1)
goto noop;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
if (!in_sack) {
/* TODO: head merge to next could be attempted here
* if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
* though it might not be worth of the additional hassle
*
* ...we can probably just fallback to what was done
* previously. We could try merging non-SACKed ones
* as well but it probably isn't going to buy off
* because later SACKs might again split them, and
* it would make skb timestamp tracking considerably
* harder problem.
*/
goto fallback;
}
len = end_seq - TCP_SKB_CB(skb)->seq;
BUG_ON(len < 0);
BUG_ON(len > skb->len);
/* MSS boundaries should be honoured or else pcount will
* severely break even though it makes things bit trickier.
* Optimize common case to avoid most of the divides
*/
mss = tcp_skb_mss(skb);
/* TODO: Fix DSACKs to not fragment already SACKed and we can
* drop this restriction as unnecessary
*/
if (mss != tcp_skb_seglen(prev))
goto fallback;
if (len == mss) {
pcount = 1;
} else if (len < mss) {
goto noop;
} else {
pcount = len / mss;
len = pcount * mss;
}
}
/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
goto fallback;
if (!skb_shift(prev, skb, len))
goto fallback;
if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
goto out;
/* Hole filled allows collapsing with the next as well, this is very
* useful when hole on every nth skb pattern happens
*/
skb = skb_rb_next(prev);
if (!skb)
goto out;
if (!skb_can_shift(skb) ||
((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
(mss != tcp_skb_seglen(skb)))
goto out;
len = skb->len;
if (skb_shift(prev, skb, len)) {
pcount += tcp_skb_pcount(skb);
tcp_shifted_skb(sk, prev, skb, state, tcp_skb_pcount(skb),
len, mss, 0);
}
out:
return prev;
noop:
return skb;
fallback:
NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
return NULL;
}
static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
struct tcp_sack_block *next_dup,
struct tcp_sacktag_state *state,
u32 start_seq, u32 end_seq,
bool dup_sack_in)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *tmp;
skb_rbtree_walk_from(skb) {
int in_sack = 0;
bool dup_sack = dup_sack_in;
/* queue is in-order => we can short-circuit the walk early */
if (!before(TCP_SKB_CB(skb)->seq, end_seq))
break;
if (next_dup &&
before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
in_sack = tcp_match_skb_to_sack(sk, skb,
next_dup->start_seq,
next_dup->end_seq);
if (in_sack > 0)
dup_sack = true;
}
/* skb reference here is a bit tricky to get right, since
* shifting can eat and free both this skb and the next,
* so not even _safe variant of the loop is enough.
*/
if (in_sack <= 0) {
tmp = tcp_shift_skb_data(sk, skb, state,
start_seq, end_seq, dup_sack);
if (tmp) {
if (tmp != skb) {
skb = tmp;
continue;
}
in_sack = 0;
} else {
in_sack = tcp_match_skb_to_sack(sk, skb,
start_seq,
end_seq);
}
}
if (unlikely(in_sack < 0))
break;
if (in_sack) {
TCP_SKB_CB(skb)->sacked =
tcp_sacktag_one(sk,
state,
TCP_SKB_CB(skb)->sacked,
TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(skb)->end_seq,
dup_sack,
tcp_skb_pcount(skb),
tcp_skb_timestamp_us(skb));
tcp_rate_skb_delivered(sk, skb, state->rate);
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
list_del_init(&skb->tcp_tsorted_anchor);
if (!before(TCP_SKB_CB(skb)->seq,
tcp_highest_sack_seq(tp)))
tcp_advance_highest_sack(sk, skb);
}
}
return skb;
}
static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
{
struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
struct sk_buff *skb;
while (*p) {
parent = *p;
skb = rb_to_skb(parent);
if (before(seq, TCP_SKB_CB(skb)->seq)) {
p = &parent->rb_left;
continue;
}
if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
p = &parent->rb_right;
continue;
}
return skb;
}
return NULL;
}
static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
u32 skip_to_seq)
{
if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
return skb;
return tcp_sacktag_bsearch(sk, skip_to_seq);
}
static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
struct sock *sk,
struct tcp_sack_block *next_dup,
struct tcp_sacktag_state *state,
u32 skip_to_seq)
{
if (!next_dup)
return skb;
if (before(next_dup->start_seq, skip_to_seq)) {
skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
skb = tcp_sacktag_walk(skb, sk, NULL, state,
next_dup->start_seq, next_dup->end_seq,
1);
}
return skb;
}
static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
{
return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
}
static int
tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
u32 prior_snd_una, struct tcp_sacktag_state *state)
{
struct tcp_sock *tp = tcp_sk(sk);
const unsigned char *ptr = (skb_transport_header(ack_skb) +
TCP_SKB_CB(ack_skb)->sacked);
struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
struct tcp_sack_block sp[TCP_NUM_SACKS];
struct tcp_sack_block *cache;
struct sk_buff *skb;
int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
int used_sacks;
bool found_dup_sack = false;
int i, j;
int first_sack_index;
state->flag = 0;
state->reord = tp->snd_nxt;
if (!tp->sacked_out)
tcp_highest_sack_reset(sk);
found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
num_sacks, prior_snd_una);
if (found_dup_sack) {
state->flag |= FLAG_DSACKING_ACK;
tp->delivered++; /* A spurious retransmission is delivered */
}
/* Eliminate too old ACKs, but take into
* account more or less fresh ones, they can
* contain valid SACK info.
*/
if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
return 0;
if (!tp->packets_out)
goto out;
used_sacks = 0;
first_sack_index = 0;
for (i = 0; i < num_sacks; i++) {
bool dup_sack = !i && found_dup_sack;
sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
if (!tcp_is_sackblock_valid(tp, dup_sack,
sp[used_sacks].start_seq,
sp[used_sacks].end_seq)) {
int mib_idx;
if (dup_sack) {
if (!tp->undo_marker)
mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
else
mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
} else {
/* Don't count olds caused by ACK reordering */
if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
!after(sp[used_sacks].end_seq, tp->snd_una))
continue;
mib_idx = LINUX_MIB_TCPSACKDISCARD;
}
NET_INC_STATS(sock_net(sk), mib_idx);
if (i == 0)
first_sack_index = -1;
continue;
}
/* Ignore very old stuff early */
if (!after(sp[used_sacks].end_seq, prior_snd_una))
continue;
used_sacks++;
}
/* order SACK blocks to allow in order walk of the retrans queue */
for (i = used_sacks - 1; i > 0; i--) {
for (j = 0; j < i; j++) {
if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
swap(sp[j], sp[j + 1]);
/* Track where the first SACK block goes to */
if (j == first_sack_index)
first_sack_index = j + 1;
}
}
}
state->mss_now = tcp_current_mss(sk);
skb = NULL;
i = 0;
if (!tp->sacked_out) {
/* It's already past, so skip checking against it */
cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
} else {
cache = tp->recv_sack_cache;
/* Skip empty blocks in at head of the cache */
while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
!cache->end_seq)
cache++;
}
while (i < used_sacks) {
u32 start_seq = sp[i].start_seq;
u32 end_seq = sp[i].end_seq;
bool dup_sack = (found_dup_sack && (i == first_sack_index));
struct tcp_sack_block *next_dup = NULL;
if (found_dup_sack && ((i + 1) == first_sack_index))
next_dup = &sp[i + 1];
/* Skip too early cached blocks */
while (tcp_sack_cache_ok(tp, cache) &&
!before(start_seq, cache->end_seq))
cache++;
/* Can skip some work by looking recv_sack_cache? */
if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
after(end_seq, cache->start_seq)) {
/* Head todo? */
if (before(start_seq, cache->start_seq)) {
skb = tcp_sacktag_skip(skb, sk, start_seq);
skb = tcp_sacktag_walk(skb, sk, next_dup,
state,
start_seq,
cache->start_seq,
dup_sack);
}
/* Rest of the block already fully processed? */
if (!after(end_seq, cache->end_seq))
goto advance_sp;
skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
state,
cache->end_seq);
/* ...tail remains todo... */
if (tcp_highest_sack_seq(tp) == cache->end_seq) {
/* ...but better entrypoint exists! */
skb = tcp_highest_sack(sk);
if (!skb)
break;
cache++;
goto walk;
}
skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
/* Check overlap against next cached too (past this one already) */
cache++;
continue;
}
if (!before(start_seq, tcp_highest_sack_seq(tp))) {
skb = tcp_highest_sack(sk);
if (!skb)
break;
}
skb = tcp_sacktag_skip(skb, sk, start_seq);
walk:
skb = tcp_sacktag_walk(skb, sk, next_dup, state,
start_seq, end_seq, dup_sack);
advance_sp:
i++;
}
/* Clear the head of the cache sack blocks so we can skip it next time */
for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
tp->recv_sack_cache[i].start_seq = 0;
tp->recv_sack_cache[i].end_seq = 0;
}
for (j = 0; j < used_sacks; j++)
tp->recv_sack_cache[i++] = sp[j];
if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
tcp_check_sack_reordering(sk, state->reord, 0);
tcp_verify_left_out(tp);
out:
#if FASTRETRANS_DEBUG > 0
WARN_ON((int)tp->sacked_out < 0);
WARN_ON((int)tp->lost_out < 0);
WARN_ON((int)tp->retrans_out < 0);
WARN_ON((int)tcp_packets_in_flight(tp) < 0);
#endif
return state->flag;
}
/* Limits sacked_out so that sum with lost_out isn't ever larger than
* packets_out. Returns false if sacked_out adjustement wasn't necessary.
*/
static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
{
u32 holes;
holes = max(tp->lost_out, 1U);
holes = min(holes, tp->packets_out);
if ((tp->sacked_out + holes) > tp->packets_out) {
tp->sacked_out = tp->packets_out - holes;
return true;
}
return false;
}
/* If we receive more dupacks than we expected counting segments
* in assumption of absent reordering, interpret this as reordering.
* The only another reason could be bug in receiver TCP.
*/
static void tcp_check_reno_reordering(struct sock *sk, const int addend)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tcp_limit_reno_sacked(tp))
return;
tp->reordering = min_t(u32, tp->packets_out + addend,
sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
tp->reord_seen++;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
}
/* Emulate SACKs for SACKless connection: account for a new dupack. */
static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
{
if (num_dupack) {
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_sacked = tp->sacked_out;
s32 delivered;
tp->sacked_out += num_dupack;
tcp_check_reno_reordering(sk, 0);
delivered = tp->sacked_out - prior_sacked;
if (delivered > 0)
tp->delivered += delivered;
tcp_verify_left_out(tp);
}
}
/* Account for ACK, ACKing some data in Reno Recovery phase. */
static void tcp_remove_reno_sacks(struct sock *sk, int acked)
{
struct tcp_sock *tp = tcp_sk(sk);
if (acked > 0) {
/* One ACK acked hole. The rest eat duplicate ACKs. */
tp->delivered += max_t(int, acked - tp->sacked_out, 1);
if (acked - 1 >= tp->sacked_out)
tp->sacked_out = 0;
else
tp->sacked_out -= acked - 1;
}
tcp_check_reno_reordering(sk, acked);
tcp_verify_left_out(tp);
}
static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
{
tp->sacked_out = 0;
}
void tcp_clear_retrans(struct tcp_sock *tp)
{
tp->retrans_out = 0;
tp->lost_out = 0;
tp->undo_marker = 0;
tp->undo_retrans = -1;
tp->sacked_out = 0;
}
static inline void tcp_init_undo(struct tcp_sock *tp)
{
tp->undo_marker = tp->snd_una;
/* Retransmission still in flight may cause DSACKs later. */
tp->undo_retrans = tp->retrans_out ? : -1;
}
static bool tcp_is_rack(const struct sock *sk)
{
return sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION;
}
/* If we detect SACK reneging, forget all SACK information
* and reset tags completely, otherwise preserve SACKs. If receiver
* dropped its ofo queue, we will know this due to reneging detection.
*/
static void tcp_timeout_mark_lost(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb, *head;
bool is_reneg; /* is receiver reneging on SACKs? */
head = tcp_rtx_queue_head(sk);
is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
if (is_reneg) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
tp->sacked_out = 0;
/* Mark SACK reneging until we recover from this loss event. */
tp->is_sack_reneg = 1;
} else if (tcp_is_reno(tp)) {
tcp_reset_reno_sack(tp);
}
skb = head;
skb_rbtree_walk_from(skb) {
if (is_reneg)
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
else if (tcp_is_rack(sk) && skb != head &&
tcp_rack_skb_timeout(tp, skb, 0) > 0)
continue; /* Don't mark recently sent ones lost yet */
tcp_mark_skb_lost(sk, skb);
}
tcp_verify_left_out(tp);
tcp_clear_all_retrans_hints(tp);
}
/* Enter Loss state. */
void tcp_enter_loss(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
tcp_timeout_mark_lost(sk);
/* Reduce ssthresh if it has not yet been made inside this window. */
if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
!after(tp->high_seq, tp->snd_una) ||
(icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->prior_cwnd = tp->snd_cwnd;
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tcp_ca_event(sk, CA_EVENT_LOSS);
tcp_init_undo(tp);
}
tp->snd_cwnd = tcp_packets_in_flight(tp) + 1;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_jiffies32;
/* Timeout in disordered state after receiving substantial DUPACKs
* suggests that the degree of reordering is over-estimated.
*/
if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
tp->reordering = min_t(unsigned int, tp->reordering,
net->ipv4.sysctl_tcp_reordering);
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->snd_nxt;
tcp_ecn_queue_cwr(tp);
/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
* loss recovery is underway except recurring timeout(s) on
* the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
*/
tp->frto = net->ipv4.sysctl_tcp_frto &&
(new_recovery || icsk->icsk_retransmits) &&
!inet_csk(sk)->icsk_mtup.probe_size;
}
/* If ACK arrived pointing to a remembered SACK, it means that our
* remembered SACKs do not reflect real state of receiver i.e.
* receiver _host_ is heavily congested (or buggy).
*
* To avoid big spurious retransmission bursts due to transient SACK
* scoreboard oddities that look like reneging, we give the receiver a
* little time (max(RTT/2, 10ms)) to send us some more ACKs that will
* restore sanity to the SACK scoreboard. If the apparent reneging
* persists until this RTO then we'll clear the SACK scoreboard.
*/
static bool tcp_check_sack_reneging(struct sock *sk, int flag)
{
if (flag & FLAG_SACK_RENEGING) {
struct tcp_sock *tp = tcp_sk(sk);
unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
msecs_to_jiffies(10));
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
delay, TCP_RTO_MAX);
return true;
}
return false;
}
/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
* counter when SACK is enabled (without SACK, sacked_out is used for
* that purpose).
*
* With reordering, holes may still be in flight, so RFC3517 recovery
* uses pure sacked_out (total number of SACKed segments) even though
* it violates the RFC that uses duplicate ACKs, often these are equal
* but when e.g. out-of-window ACKs or packet duplication occurs,
* they differ. Since neither occurs due to loss, TCP should really
* ignore them.
*/
static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
{
return tp->sacked_out + 1;
}
/* Linux NewReno/SACK/ECN state machine.
* --------------------------------------
*
* "Open" Normal state, no dubious events, fast path.
* "Disorder" In all the respects it is "Open",
* but requires a bit more attention. It is entered when
* we see some SACKs or dupacks. It is split of "Open"
* mainly to move some processing from fast path to slow one.
* "CWR" CWND was reduced due to some Congestion Notification event.
* It can be ECN, ICMP source quench, local device congestion.
* "Recovery" CWND was reduced, we are fast-retransmitting.
* "Loss" CWND was reduced due to RTO timeout or SACK reneging.
*
* tcp_fastretrans_alert() is entered:
* - each incoming ACK, if state is not "Open"
* - when arrived ACK is unusual, namely:
* * SACK
* * Duplicate ACK.
* * ECN ECE.
*
* Counting packets in flight is pretty simple.
*
* in_flight = packets_out - left_out + retrans_out
*
* packets_out is SND.NXT-SND.UNA counted in packets.
*
* retrans_out is number of retransmitted segments.
*
* left_out is number of segments left network, but not ACKed yet.
*
* left_out = sacked_out + lost_out
*
* sacked_out: Packets, which arrived to receiver out of order
* and hence not ACKed. With SACKs this number is simply
* amount of SACKed data. Even without SACKs
* it is easy to give pretty reliable estimate of this number,
* counting duplicate ACKs.
*
* lost_out: Packets lost by network. TCP has no explicit
* "loss notification" feedback from network (for now).
* It means that this number can be only _guessed_.
* Actually, it is the heuristics to predict lossage that
* distinguishes different algorithms.
*
* F.e. after RTO, when all the queue is considered as lost,
* lost_out = packets_out and in_flight = retrans_out.
*
* Essentially, we have now a few algorithms detecting
* lost packets.
*
* If the receiver supports SACK:
*
* RFC6675/3517: It is the conventional algorithm. A packet is
* considered lost if the number of higher sequence packets
* SACKed is greater than or equal the DUPACK thoreshold
* (reordering). This is implemented in tcp_mark_head_lost and
* tcp_update_scoreboard.
*
* RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
* (2017-) that checks timing instead of counting DUPACKs.
* Essentially a packet is considered lost if it's not S/ACKed
* after RTT + reordering_window, where both metrics are
* dynamically measured and adjusted. This is implemented in
* tcp_rack_mark_lost.
*
* If the receiver does not support SACK:
*
* NewReno (RFC6582): in Recovery we assume that one segment
* is lost (classic Reno). While we are in Recovery and
* a partial ACK arrives, we assume that one more packet
* is lost (NewReno). This heuristics are the same in NewReno
* and SACK.
*
* Really tricky (and requiring careful tuning) part of algorithm
* is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
* The first determines the moment _when_ we should reduce CWND and,
* hence, slow down forward transmission. In fact, it determines the moment
* when we decide that hole is caused by loss, rather than by a reorder.
*
* tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
* holes, caused by lost packets.
*
* And the most logically complicated part of algorithm is undo
* heuristics. We detect false retransmits due to both too early
* fast retransmit (reordering) and underestimated RTO, analyzing
* timestamps and D-SACKs. When we detect that some segments were
* retransmitted by mistake and CWND reduction was wrong, we undo
* window reduction and abort recovery phase. This logic is hidden
* inside several functions named tcp_try_undo_<something>.
*/
/* This function decides, when we should leave Disordered state
* and enter Recovery phase, reducing congestion window.
*
* Main question: may we further continue forward transmission
* with the same cwnd?
*/
static bool tcp_time_to_recover(struct sock *sk, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Trick#1: The loss is proven. */
if (tp->lost_out)
return true;
/* Not-A-Trick#2 : Classic rule... */
if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
return true;
return false;
}
/* Detect loss in event "A" above by marking head of queue up as lost.
* For non-SACK(Reno) senders, the first "packets" number of segments
* are considered lost. For RFC3517 SACK, a segment is considered lost if it
* has at least tp->reordering SACKed seqments above it; "packets" refers to
* the maximum SACKed segments to pass before reaching this limit.
*/
static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int cnt, oldcnt, lost;
unsigned int mss;
/* Use SACK to deduce losses of new sequences sent during recovery */
const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
WARN_ON(packets > tp->packets_out);
skb = tp->lost_skb_hint;
if (skb) {
/* Head already handled? */
if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
return;
cnt = tp->lost_cnt_hint;
} else {
skb = tcp_rtx_queue_head(sk);
cnt = 0;
}
skb_rbtree_walk_from(skb) {
/* TODO: do this better */
/* this is not the most efficient way to do this... */
tp->lost_skb_hint = skb;
tp->lost_cnt_hint = cnt;
if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
break;
oldcnt = cnt;
if (tcp_is_reno(tp) ||
(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
cnt += tcp_skb_pcount(skb);
if (cnt > packets) {
if (tcp_is_sack(tp) ||
(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
(oldcnt >= packets))
break;
mss = tcp_skb_mss(skb);
/* If needed, chop off the prefix to mark as lost. */
lost = (packets - oldcnt) * mss;
if (lost < skb->len &&
tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
lost, mss, GFP_ATOMIC) < 0)
break;
cnt = packets;
}
tcp_skb_mark_lost(tp, skb);
if (mark_head)
break;
}
tcp_verify_left_out(tp);
}
/* Account newly detected lost packet(s) */
static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_is_sack(tp)) {
int sacked_upto = tp->sacked_out - tp->reordering;
if (sacked_upto >= 0)
tcp_mark_head_lost(sk, sacked_upto, 0);
else if (fast_rexmit)
tcp_mark_head_lost(sk, 1, 1);
}
}
static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
{
return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
before(tp->rx_opt.rcv_tsecr, when);
}
/* skb is spurious retransmitted if the returned timestamp echo
* reply is prior to the skb transmission time
*/
static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
const struct sk_buff *skb)
{
return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
}
/* Nothing was retransmitted or returned timestamp is less
* than timestamp of the first retransmission.
*/
static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
{
return tp->retrans_stamp &&
tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
}
/* Undo procedures. */
/* We can clear retrans_stamp when there are no retransmissions in the
* window. It would seem that it is trivially available for us in
* tp->retrans_out, however, that kind of assumptions doesn't consider
* what will happen if errors occur when sending retransmission for the
* second time. ...It could the that such segment has only
* TCPCB_EVER_RETRANS set at the present time. It seems that checking
* the head skb is enough except for some reneging corner cases that
* are not worth the effort.
*
* Main reason for all this complexity is the fact that connection dying
* time now depends on the validity of the retrans_stamp, in particular,
* that successive retransmissions of a segment must not advance
* retrans_stamp under any conditions.
*/
static bool tcp_any_retrans_done(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
if (tp->retrans_out)
return true;
skb = tcp_rtx_queue_head(sk);
if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
return true;
return false;
}
static void DBGUNDO(struct sock *sk, const char *msg)
{
#if FASTRETRANS_DEBUG > 1
struct tcp_sock *tp = tcp_sk(sk);
struct inet_sock *inet = inet_sk(sk);
if (sk->sk_family == AF_INET) {
pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
msg,
&inet->inet_daddr, ntohs(inet->inet_dport),
tp->snd_cwnd, tcp_left_out(tp),
tp->snd_ssthresh, tp->prior_ssthresh,
tp->packets_out);
}
#if IS_ENABLED(CONFIG_IPV6)
else if (sk->sk_family == AF_INET6) {
pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
msg,
&sk->sk_v6_daddr, ntohs(inet->inet_dport),
tp->snd_cwnd, tcp_left_out(tp),
tp->snd_ssthresh, tp->prior_ssthresh,
tp->packets_out);
}
#endif
#endif
}
static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
{
struct tcp_sock *tp = tcp_sk(sk);
if (unmark_loss) {
struct sk_buff *skb;
skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
}
tp->lost_out = 0;
tcp_clear_all_retrans_hints(tp);
}
if (tp->prior_ssthresh) {
const struct inet_connection_sock *icsk = inet_csk(sk);
tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
if (tp->prior_ssthresh > tp->snd_ssthresh) {
tp->snd_ssthresh = tp->prior_ssthresh;
tcp_ecn_withdraw_cwr(tp);
}
}
tp->snd_cwnd_stamp = tcp_jiffies32;
tp->undo_marker = 0;
tp->rack.advanced = 1; /* Force RACK to re-exam losses */
}
static inline bool tcp_may_undo(const struct tcp_sock *tp)
{
return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
}
/* People celebrate: "We love our President!" */
static bool tcp_try_undo_recovery(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_may_undo(tp)) {
int mib_idx;
/* Happy end! We did not retransmit anything
* or our original transmission succeeded.
*/
DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
tcp_undo_cwnd_reduction(sk, false);
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
mib_idx = LINUX_MIB_TCPLOSSUNDO;
else
mib_idx = LINUX_MIB_TCPFULLUNDO;
NET_INC_STATS(sock_net(sk), mib_idx);
} else if (tp->rack.reo_wnd_persist) {
tp->rack.reo_wnd_persist--;
}
if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
/* Hold old state until something *above* high_seq
* is ACKed. For Reno it is MUST to prevent false
* fast retransmits (RFC2582). SACK TCP is safe. */
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
return true;
}
tcp_set_ca_state(sk, TCP_CA_Open);
tp->is_sack_reneg = 0;
return false;
}
/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
static bool tcp_try_undo_dsack(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->undo_marker && !tp->undo_retrans) {
tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
tp->rack.reo_wnd_persist + 1);
DBGUNDO(sk, "D-SACK");
tcp_undo_cwnd_reduction(sk, false);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
return true;
}
return false;
}
/* Undo during loss recovery after partial ACK or using F-RTO. */
static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
{
struct tcp_sock *tp = tcp_sk(sk);
if (frto_undo || tcp_may_undo(tp)) {
tcp_undo_cwnd_reduction(sk, true);
DBGUNDO(sk, "partial loss");
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
if (frto_undo)
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPSPURIOUSRTOS);
inet_csk(sk)->icsk_retransmits = 0;
if (frto_undo || tcp_is_sack(tp)) {
tcp_set_ca_state(sk, TCP_CA_Open);
tp->is_sack_reneg = 0;
}
return true;
}
return false;
}
/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
* It computes the number of packets to send (sndcnt) based on packets newly
* delivered:
* 1) If the packets in flight is larger than ssthresh, PRR spreads the
* cwnd reductions across a full RTT.
* 2) Otherwise PRR uses packet conservation to send as much as delivered.
* But when the retransmits are acked without further losses, PRR
* slow starts cwnd up to ssthresh to speed up the recovery.
*/
static void tcp_init_cwnd_reduction(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->high_seq = tp->snd_nxt;
tp->tlp_high_seq = 0;
tp->snd_cwnd_cnt = 0;
tp->prior_cwnd = tp->snd_cwnd;
tp->prr_delivered = 0;
tp->prr_out = 0;
tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
tcp_ecn_queue_cwr(tp);
}
void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
int sndcnt = 0;
int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
return;
tp->prr_delivered += newly_acked_sacked;
if (delta < 0) {
u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
tp->prior_cwnd - 1;
sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
} else if ((flag & (FLAG_RETRANS_DATA_ACKED | FLAG_LOST_RETRANS)) ==
FLAG_RETRANS_DATA_ACKED) {
sndcnt = min_t(int, delta,
max_t(int, tp->prr_delivered - tp->prr_out,
newly_acked_sacked) + 1);
} else {
sndcnt = min(delta, newly_acked_sacked);
}
/* Force a fast retransmit upon entering fast recovery */
sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
}
static inline void tcp_end_cwnd_reduction(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (inet_csk(sk)->icsk_ca_ops->cong_control)
return;
/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
(inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
tp->snd_cwnd = tp->snd_ssthresh;
tp->snd_cwnd_stamp = tcp_jiffies32;
}
tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
}
/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
void tcp_enter_cwr(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->prior_ssthresh = 0;
if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
tp->undo_marker = 0;
tcp_init_cwnd_reduction(sk);
tcp_set_ca_state(sk, TCP_CA_CWR);
}
}
EXPORT_SYMBOL(tcp_enter_cwr);
static void tcp_try_keep_open(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int state = TCP_CA_Open;
if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
state = TCP_CA_Disorder;
if (inet_csk(sk)->icsk_ca_state != state) {
tcp_set_ca_state(sk, state);
tp->high_seq = tp->snd_nxt;
}
}
static void tcp_try_to_open(struct sock *sk, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
tcp_verify_left_out(tp);
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
if (flag & FLAG_ECE)
tcp_enter_cwr(sk);
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
tcp_try_keep_open(sk);
}
}
static void tcp_mtup_probe_failed(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
icsk->icsk_mtup.probe_size = 0;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
}
static void tcp_mtup_probe_success(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
/* FIXME: breaks with very large cwnd */
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_cwnd = tp->snd_cwnd *
tcp_mss_to_mtu(sk, tp->mss_cache) /
icsk->icsk_mtup.probe_size;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_jiffies32;
tp->snd_ssthresh = tcp_current_ssthresh(sk);
icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
icsk->icsk_mtup.probe_size = 0;
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
}
/* Do a simple retransmit without using the backoff mechanisms in
* tcp_timer. This is used for path mtu discovery.
* The socket is already locked here.
*/
void tcp_simple_retransmit(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
unsigned int mss = tcp_current_mss(sk);
skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
if (tcp_skb_seglen(skb) > mss &&
!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= tcp_skb_pcount(skb);
}
tcp_skb_mark_lost_uncond_verify(tp, skb);
}
}
tcp_clear_retrans_hints_partial(tp);
if (!tp->lost_out)
return;
if (tcp_is_reno(tp))
tcp_limit_reno_sacked(tp);
tcp_verify_left_out(tp);
/* Don't muck with the congestion window here.
* Reason is that we do not increase amount of _data_
* in network, but units changed and effective
* cwnd/ssthresh really reduced now.
*/
if (icsk->icsk_ca_state != TCP_CA_Loss) {
tp->high_seq = tp->snd_nxt;
tp->snd_ssthresh = tcp_current_ssthresh(sk);
tp->prior_ssthresh = 0;
tp->undo_marker = 0;
tcp_set_ca_state(sk, TCP_CA_Loss);
}
tcp_xmit_retransmit_queue(sk);
}
EXPORT_SYMBOL(tcp_simple_retransmit);
void tcp_enter_recovery(struct sock *sk, bool ece_ack)
{
struct tcp_sock *tp = tcp_sk(sk);
int mib_idx;
if (tcp_is_reno(tp))
mib_idx = LINUX_MIB_TCPRENORECOVERY;
else
mib_idx = LINUX_MIB_TCPSACKRECOVERY;
NET_INC_STATS(sock_net(sk), mib_idx);
tp->prior_ssthresh = 0;
tcp_init_undo(tp);
if (!tcp_in_cwnd_reduction(sk)) {
if (!ece_ack)
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tcp_init_cwnd_reduction(sk);
}
tcp_set_ca_state(sk, TCP_CA_Recovery);
}
/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
* recovered or spurious. Otherwise retransmits more on partial ACKs.
*/
static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
int *rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
bool recovered = !before(tp->snd_una, tp->high_seq);
if ((flag & FLAG_SND_UNA_ADVANCED) &&
tcp_try_undo_loss(sk, false))
return;
if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
/* Step 3.b. A timeout is spurious if not all data are
* lost, i.e., never-retransmitted data are (s)acked.
*/
if ((flag & FLAG_ORIG_SACK_ACKED) &&
tcp_try_undo_loss(sk, true))
return;
if (after(tp->snd_nxt, tp->high_seq)) {
if (flag & FLAG_DATA_SACKED || num_dupack)
tp->frto = 0; /* Step 3.a. loss was real */
} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
tp->high_seq = tp->snd_nxt;
/* Step 2.b. Try send new data (but deferred until cwnd
* is updated in tcp_ack()). Otherwise fall back to
* the conventional recovery.
*/
if (!tcp_write_queue_empty(sk) &&
after(tcp_wnd_end(tp), tp->snd_nxt)) {
*rexmit = REXMIT_NEW;
return;
}
tp->frto = 0;
}
}
if (recovered) {
/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
tcp_try_undo_recovery(sk);
return;
}
if (tcp_is_reno(tp)) {
/* A Reno DUPACK means new data in F-RTO step 2.b above are
* delivered. Lower inflight to clock out (re)tranmissions.
*/
if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
tcp_add_reno_sack(sk, num_dupack);
else if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
}
*rexmit = REXMIT_LOST;
}
/* Undo during fast recovery after partial ACK. */
static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->undo_marker && tcp_packet_delayed(tp)) {
/* Plain luck! Hole if filled with delayed
* packet, rather than with a retransmit. Check reordering.
*/
tcp_check_sack_reordering(sk, prior_snd_una, 1);
/* We are getting evidence that the reordering degree is higher
* than we realized. If there are no retransmits out then we
* can undo. Otherwise we clock out new packets but do not
* mark more packets lost or retransmit more.
*/
if (tp->retrans_out)
return true;
if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
DBGUNDO(sk, "partial recovery");
tcp_undo_cwnd_reduction(sk, true);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
tcp_try_keep_open(sk);
return true;
}
return false;
}
static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_rtx_queue_empty(sk))
return;
if (unlikely(tcp_is_reno(tp))) {
tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
} else if (tcp_is_rack(sk)) {
u32 prior_retrans = tp->retrans_out;
tcp_rack_mark_lost(sk);
if (prior_retrans > tp->retrans_out)
*ack_flag |= FLAG_LOST_RETRANS;
}
}
static bool tcp_force_fast_retransmit(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
return after(tcp_highest_sack_seq(tp),
tp->snd_una + tp->reordering * tp->mss_cache);
}
/* Process an event, which can update packets-in-flight not trivially.
* Main goal of this function is to calculate new estimate for left_out,
* taking into account both packets sitting in receiver's buffer and
* packets lost by network.
*
* Besides that it updates the congestion state when packet loss or ECN
* is detected. But it does not reduce the cwnd, it is done by the
* congestion control later.
*
* It does _not_ decide what to send, it is made in function
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
int num_dupack, int *ack_flag, int *rexmit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int fast_rexmit = 0, flag = *ack_flag;
bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
tcp_force_fast_retransmit(sk));
if (!tp->packets_out && tp->sacked_out)
tp->sacked_out = 0;
/* Now state machine starts.
* A. ECE, hence prohibit cwnd undoing, the reduction is required. */
if (flag & FLAG_ECE)
tp->prior_ssthresh = 0;
/* B. In all the states check for reneging SACKs. */
if (tcp_check_sack_reneging(sk, flag))
return;
/* C. Check consistency of the current state. */
tcp_verify_left_out(tp);
/* D. Check state exit conditions. State can be terminated
* when high_seq is ACKed. */
if (icsk->icsk_ca_state == TCP_CA_Open) {
WARN_ON(tp->retrans_out != 0);
tp->retrans_stamp = 0;
} else if (!before(tp->snd_una, tp->high_seq)) {
switch (icsk->icsk_ca_state) {
case TCP_CA_CWR:
/* CWR is to be held something *above* high_seq
* is ACKed for CWR bit to reach receiver. */
if (tp->snd_una != tp->high_seq) {
tcp_end_cwnd_reduction(sk);
tcp_set_ca_state(sk, TCP_CA_Open);
}
break;
case TCP_CA_Recovery:
if (tcp_is_reno(tp))
tcp_reset_reno_sack(tp);
if (tcp_try_undo_recovery(sk))
return;
tcp_end_cwnd_reduction(sk);
break;
}
}
/* E. Process state. */
switch (icsk->icsk_ca_state) {
case TCP_CA_Recovery:
if (!(flag & FLAG_SND_UNA_ADVANCED)) {
if (tcp_is_reno(tp))
tcp_add_reno_sack(sk, num_dupack);
} else {
if (tcp_try_undo_partial(sk, prior_snd_una))
return;
/* Partial ACK arrived. Force fast retransmit. */
do_lost = tcp_is_reno(tp) ||
tcp_force_fast_retransmit(sk);
}
if (tcp_try_undo_dsack(sk)) {
tcp_try_keep_open(sk);
return;
}
tcp_identify_packet_loss(sk, ack_flag);
break;
case TCP_CA_Loss:
tcp_process_loss(sk, flag, num_dupack, rexmit);
tcp_identify_packet_loss(sk, ack_flag);
if (!(icsk->icsk_ca_state == TCP_CA_Open ||
(*ack_flag & FLAG_LOST_RETRANS)))
return;
/* Change state if cwnd is undone or retransmits are lost */
/* fall through */
default:
if (tcp_is_reno(tp)) {
if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
tcp_add_reno_sack(sk, num_dupack);
}
if (icsk->icsk_ca_state <= TCP_CA_Disorder)
tcp_try_undo_dsack(sk);
tcp_identify_packet_loss(sk, ack_flag);
if (!tcp_time_to_recover(sk, flag)) {
tcp_try_to_open(sk, flag);
return;
}
/* MTU probe failure: don't reduce cwnd */
if (icsk->icsk_ca_state < TCP_CA_CWR &&
icsk->icsk_mtup.probe_size &&
tp->snd_una == tp->mtu_probe.probe_seq_start) {
tcp_mtup_probe_failed(sk);
/* Restores the reduction we did in tcp_mtup_probe() */
tp->snd_cwnd++;
tcp_simple_retransmit(sk);
return;
}
/* Otherwise enter Recovery state */
tcp_enter_recovery(sk, (flag & FLAG_ECE));
fast_rexmit = 1;
}
if (!tcp_is_rack(sk) && do_lost)
tcp_update_scoreboard(sk, fast_rexmit);
*rexmit = REXMIT_LOST;
}
static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
{
u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;
struct tcp_sock *tp = tcp_sk(sk);
if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
/* If the remote keeps returning delayed ACKs, eventually
* the min filter would pick it up and overestimate the
* prop. delay when it expires. Skip suspected delayed ACKs.
*/
return;
}
minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
rtt_us ? : jiffies_to_usecs(1));
}
static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
long seq_rtt_us, long sack_rtt_us,
long ca_rtt_us, struct rate_sample *rs)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
* broken middle-boxes or peers may corrupt TS-ECR fields. But
* Karn's algorithm forbids taking RTT if some retransmitted data
* is acked (RFC6298).
*/
if (seq_rtt_us < 0)
seq_rtt_us = sack_rtt_us;
/* RTTM Rule: A TSecr value received in a segment is used to
* update the averaged RTT measurement only if the segment
* acknowledges some new data, i.e., only if it advances the
* left edge of the send window.
* See draft-ietf-tcplw-high-performance-00, section 3.3.
*/
if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
flag & FLAG_ACKED) {
u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
ca_rtt_us = seq_rtt_us;
}
}
rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
if (seq_rtt_us < 0)
return false;
/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
* always taken together with ACK, SACK, or TS-opts. Any negative
* values will be skipped with the seq_rtt_us < 0 check above.
*/
tcp_update_rtt_min(sk, ca_rtt_us, flag);
tcp_rtt_estimator(sk, seq_rtt_us);
tcp_set_rto(sk);
/* RFC6298: only reset backoff on valid RTT measurement. */
inet_csk(sk)->icsk_backoff = 0;
return true;
}
/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
{
struct rate_sample rs;
long rtt_us = -1L;
if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
}
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
}
/* Restart timer after forward progress on connection.
* RFC2988 recommends to restart timer to now+rto.
*/
void tcp_rearm_rto(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
/* If the retrans timer is currently being used by Fast Open
* for SYN-ACK retrans purpose, stay put.
*/
if (tp->fastopen_rsk)
return;
if (!tp->packets_out) {
inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
} else {
u32 rto = inet_csk(sk)->icsk_rto;
/* Offset the time elapsed after installing regular RTO */
if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
s64 delta_us = tcp_rto_delta_us(sk);
/* delta_us may not be positive if the socket is locked
* when the retrans timer fires and is rescheduled.
*/
rto = usecs_to_jiffies(max_t(int, delta_us, 1));
}
tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
TCP_RTO_MAX, tcp_rtx_queue_head(sk));
}
}
/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
static void tcp_set_xmit_timer(struct sock *sk)
{
if (!tcp_schedule_loss_probe(sk, true))
tcp_rearm_rto(sk);
}
/* If we get here, the whole TSO packet has not been acked. */
static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 packets_acked;
BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
packets_acked = tcp_skb_pcount(skb);
if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
return 0;
packets_acked -= tcp_skb_pcount(skb);
if (packets_acked) {
BUG_ON(tcp_skb_pcount(skb) == 0);
BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
}
return packets_acked;
}
static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
u32 prior_snd_una)
{
const struct skb_shared_info *shinfo;
/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
return;
shinfo = skb_shinfo(skb);
if (!before(shinfo->tskey, prior_snd_una) &&
before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
tcp_skb_tsorted_save(skb) {
__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
} tcp_skb_tsorted_restore(skb);
}
}
/* Remove acknowledged frames from the retransmission queue. If our packet
* is before the ack sequence we can discard it as it's confirmed to have
* arrived at the other end.
*/
static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
u32 prior_snd_una,
struct tcp_sacktag_state *sack)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
u64 first_ackt, last_ackt;
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_sacked = tp->sacked_out;
u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
struct sk_buff *skb, *next;
bool fully_acked = true;
long sack_rtt_us = -1L;
long seq_rtt_us = -1L;
long ca_rtt_us = -1L;
u32 pkts_acked = 0;
u32 last_in_flight = 0;
bool rtt_update;
int flag = 0;
first_ackt = 0;
for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
const u32 start_seq = scb->seq;
u8 sacked = scb->sacked;
u32 acked_pcount;
tcp_ack_tstamp(sk, skb, prior_snd_una);
/* Determine how many packets and what bytes were acked, tso and else */
if (after(scb->end_seq, tp->snd_una)) {
if (tcp_skb_pcount(skb) == 1 ||
!after(tp->snd_una, scb->seq))
break;
acked_pcount = tcp_tso_acked(sk, skb);
if (!acked_pcount)
break;
fully_acked = false;
} else {
acked_pcount = tcp_skb_pcount(skb);
}
if (unlikely(sacked & TCPCB_RETRANS)) {
if (sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= acked_pcount;
flag |= FLAG_RETRANS_DATA_ACKED;
} else if (!(sacked & TCPCB_SACKED_ACKED)) {
last_ackt = tcp_skb_timestamp_us(skb);
WARN_ON_ONCE(last_ackt == 0);
if (!first_ackt)
first_ackt = last_ackt;
last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
if (before(start_seq, reord))
reord = start_seq;
if (!after(scb->end_seq, tp->high_seq))
flag |= FLAG_ORIG_SACK_ACKED;
}
if (sacked & TCPCB_SACKED_ACKED) {
tp->sacked_out -= acked_pcount;
} else if (tcp_is_sack(tp)) {
tp->delivered += acked_pcount;
if (!tcp_skb_spurious_retrans(tp, skb))
tcp_rack_advance(tp, sacked, scb->end_seq,
tcp_skb_timestamp_us(skb));
}
if (sacked & TCPCB_LOST)
tp->lost_out -= acked_pcount;
tp->packets_out -= acked_pcount;
pkts_acked += acked_pcount;
tcp_rate_skb_delivered(sk, skb, sack->rate);
/* Initial outgoing SYN's get put onto the write_queue
* just like anything else we transmit. It is not
* true data, and if we misinform our callers that
* this ACK acks real data, we will erroneously exit
* connection startup slow start one packet too
* quickly. This is severely frowned upon behavior.
*/
if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
flag |= FLAG_DATA_ACKED;
} else {
flag |= FLAG_SYN_ACKED;
tp->retrans_stamp = 0;
}
if (!fully_acked)
break;
next = skb_rb_next(skb);
if (unlikely(skb == tp->retransmit_skb_hint))
tp->retransmit_skb_hint = NULL;
if (unlikely(skb == tp->lost_skb_hint))
tp->lost_skb_hint = NULL;
tcp_rtx_queue_unlink_and_free(skb, sk);
}
if (!skb)
tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
tp->snd_up = tp->snd_una;
if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
flag |= FLAG_SACK_RENEGING;
if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
if (pkts_acked == 1 && last_in_flight < tp->mss_cache &&
last_in_flight && !prior_sacked && fully_acked &&
sack->rate->prior_delivered + 1 == tp->delivered &&
!(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
/* Conservatively mark a delayed ACK. It's typically
* from a lone runt packet over the round trip to
* a receiver w/o out-of-order or CE events.
*/
flag |= FLAG_ACK_MAYBE_DELAYED;
}
}
if (sack->first_sackt) {
sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
}
rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
ca_rtt_us, sack->rate);
if (flag & FLAG_ACKED) {
flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
if (unlikely(icsk->icsk_mtup.probe_size &&
!after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
tcp_mtup_probe_success(sk);
}
if (tcp_is_reno(tp)) {
tcp_remove_reno_sacks(sk, pkts_acked);
/* If any of the cumulatively ACKed segments was
* retransmitted, non-SACK case cannot confirm that
* progress was due to original transmission due to
* lack of TCPCB_SACKED_ACKED bits even if some of
* the packets may have been never retransmitted.
*/
if (flag & FLAG_RETRANS_DATA_ACKED)
flag &= ~FLAG_ORIG_SACK_ACKED;
} else {
int delta;
/* Non-retransmitted hole got filled? That's reordering */
if (before(reord, prior_fack))
tcp_check_sack_reordering(sk, reord, 0);
delta = prior_sacked - tp->sacked_out;
tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
}
} else if (skb && rtt_update && sack_rtt_us >= 0 &&
sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
tcp_skb_timestamp_us(skb))) {
/* Do not re-arm RTO if the sack RTT is measured from data sent
* after when the head was last (re)transmitted. Otherwise the
* timeout may continue to extend in loss recovery.
*/
flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
}
if (icsk->icsk_ca_ops->pkts_acked) {
struct ack_sample sample = { .pkts_acked = pkts_acked,
.rtt_us = sack->rate->rtt_us,
.in_flight = last_in_flight };
icsk->icsk_ca_ops->pkts_acked(sk, &sample);
}
#if FASTRETRANS_DEBUG > 0
WARN_ON((int)tp->sacked_out < 0);
WARN_ON((int)tp->lost_out < 0);
WARN_ON((int)tp->retrans_out < 0);
if (!tp->packets_out && tcp_is_sack(tp)) {
icsk = inet_csk(sk);
if (tp->lost_out) {
pr_debug("Leak l=%u %d\n",
tp->lost_out, icsk->icsk_ca_state);
tp->lost_out = 0;
}
if (tp->sacked_out) {
pr_debug("Leak s=%u %d\n",
tp->sacked_out, icsk->icsk_ca_state);
tp->sacked_out = 0;
}
if (tp->retrans_out) {
pr_debug("Leak r=%u %d\n",
tp->retrans_out, icsk->icsk_ca_state);
tp->retrans_out = 0;
}
}
#endif
return flag;
}
static void tcp_ack_probe(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct sk_buff *head = tcp_send_head(sk);
const struct tcp_sock *tp = tcp_sk(sk);
/* Was it a usable window open? */
if (!head)
return;
if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
icsk->icsk_backoff = 0;
inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
/* Socket must be waked up by subsequent tcp_data_snd_check().
* This function is not for random using!
*/
} else {
unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
when, TCP_RTO_MAX, NULL);
}
}
static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
{
return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
}
/* Decide wheather to run the increase function of congestion control. */
static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
{
/* If reordering is high then always grow cwnd whenever data is
* delivered regardless of its ordering. Otherwise stay conservative
* and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
* new SACK or ECE mark may first advance cwnd here and later reduce
* cwnd in tcp_fastretrans_alert() based on more states.
*/
if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
return flag & FLAG_FORWARD_PROGRESS;
return flag & FLAG_DATA_ACKED;
}
/* The "ultimate" congestion control function that aims to replace the rigid
* cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
* It's called toward the end of processing an ACK with precise rate
* information. All transmission or retransmission are delayed afterwards.
*/
static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
int flag, const struct rate_sample *rs)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->cong_control) {
icsk->icsk_ca_ops->cong_control(sk, rs);
return;
}
if (tcp_in_cwnd_reduction(sk)) {
/* Reduce cwnd if state mandates */
tcp_cwnd_reduction(sk, acked_sacked, flag);
} else if (tcp_may_raise_cwnd(sk, flag)) {
/* Advance cwnd if state allows */
tcp_cong_avoid(sk, ack, acked_sacked);
}
tcp_update_pacing_rate(sk);
}
/* Check that window update is acceptable.
* The function assumes that snd_una<=ack<=snd_next.
*/
static inline bool tcp_may_update_window(const struct tcp_sock *tp,
const u32 ack, const u32 ack_seq,
const u32 nwin)
{
return after(ack, tp->snd_una) ||
after(ack_seq, tp->snd_wl1) ||
(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
}
/* If we update tp->snd_una, also update tp->bytes_acked */
static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
{
u32 delta = ack - tp->snd_una;
sock_owned_by_me((struct sock *)tp);
tp->bytes_acked += delta;
tp->snd_una = ack;
}
/* If we update tp->rcv_nxt, also update tp->bytes_received */
static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
{
u32 delta = seq - tp->rcv_nxt;
sock_owned_by_me((struct sock *)tp);
tp->bytes_received += delta;
tp->rcv_nxt = seq;
}
/* Update our send window.
*
* Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
* and in FreeBSD. NetBSD's one is even worse.) is wrong.
*/
static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
u32 ack_seq)
{
struct tcp_sock *tp = tcp_sk(sk);
int flag = 0;
u32 nwin = ntohs(tcp_hdr(skb)->window);
if (likely(!tcp_hdr(skb)->syn))
nwin <<= tp->rx_opt.snd_wscale;
if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
flag |= FLAG_WIN_UPDATE;
tcp_update_wl(tp, ack_seq);
if (tp->snd_wnd != nwin) {
tp->snd_wnd = nwin;
/* Note, it is the only place, where
* fast path is recovered for sending TCP.
*/
tp->pred_flags = 0;
tcp_fast_path_check(sk);
if (!tcp_write_queue_empty(sk))
tcp_slow_start_after_idle_check(sk);
if (nwin > tp->max_window) {
tp->max_window = nwin;
tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
}
}
}
tcp_snd_una_update(tp, ack);
return flag;
}
static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
u32 *last_oow_ack_time)
{
if (*last_oow_ack_time) {
s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
NET_INC_STATS(net, mib_idx);
return true; /* rate-limited: don't send yet! */
}
}
*last_oow_ack_time = tcp_jiffies32;
return false; /* not rate-limited: go ahead, send dupack now! */
}
/* Return true if we're currently rate-limiting out-of-window ACKs and
* thus shouldn't send a dupack right now. We rate-limit dupacks in
* response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
* attacks that send repeated SYNs or ACKs for the same connection. To
* do this, we do not send a duplicate SYNACK or ACK if the remote
* endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
*/
bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
int mib_idx, u32 *last_oow_ack_time)
{
/* Data packets without SYNs are not likely part of an ACK loop. */
if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
!tcp_hdr(skb)->syn)
return false;
return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
}
/* RFC 5961 7 [ACK Throttling] */
static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
{
/* unprotected vars, we dont care of overwrites */
static u32 challenge_timestamp;
static unsigned int challenge_count;
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
u32 count, now;
/* First check our per-socket dupack rate limit. */
if (__tcp_oow_rate_limited(net,
LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
&tp->last_oow_ack_time))
return;
/* Then check host-wide RFC 5961 rate limit. */
now = jiffies / HZ;
if (now != challenge_timestamp) {
u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
u32 half = (ack_limit + 1) >> 1;
challenge_timestamp = now;
WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
}
count = READ_ONCE(challenge_count);
if (count > 0) {
WRITE_ONCE(challenge_count, count - 1);
NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
tcp_send_ack(sk);
}
}
static void tcp_store_ts_recent(struct tcp_sock *tp)
{
tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
}
static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
{
if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
/* PAWS bug workaround wrt. ACK frames, the PAWS discard
* extra check below makes sure this can only happen
* for pure ACK frames. -DaveM
*
* Not only, also it occurs for expired timestamps.
*/
if (tcp_paws_check(&tp->rx_opt, 0))
tcp_store_ts_recent(tp);
}
}
/* This routine deals with acks during a TLP episode.
* We mark the end of a TLP episode on receiving TLP dupack or when
* ack is after tlp_high_seq.
* Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
*/
static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
if (before(ack, tp->tlp_high_seq))
return;
if (flag & FLAG_DSACKING_ACK) {
/* This DSACK means original and TLP probe arrived; no loss */
tp->tlp_high_seq = 0;
} else if (after(ack, tp->tlp_high_seq)) {
/* ACK advances: there was a loss, so reduce cwnd. Reset
* tlp_high_seq in tcp_init_cwnd_reduction()
*/
tcp_init_cwnd_reduction(sk);
tcp_set_ca_state(sk, TCP_CA_CWR);
tcp_end_cwnd_reduction(sk);
tcp_try_keep_open(sk);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPLOSSPROBERECOVERY);
} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
/* Pure dupack: original and TLP probe arrived; no loss */
tp->tlp_high_seq = 0;
}
}
static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->in_ack_event)
icsk->icsk_ca_ops->in_ack_event(sk, flags);
}
/* Congestion control has updated the cwnd already. So if we're in
* loss recovery then now we do any new sends (for FRTO) or
* retransmits (for CA_Loss or CA_recovery) that make sense.
*/
static void tcp_xmit_recovery(struct sock *sk, int rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
return;
if (unlikely(rexmit == 2)) {
__tcp_push_pending_frames(sk, tcp_current_mss(sk),
TCP_NAGLE_OFF);
if (after(tp->snd_nxt, tp->high_seq))
return;
tp->frto = 0;
}
tcp_xmit_retransmit_queue(sk);
}
/* Returns the number of packets newly acked or sacked by the current ACK */
static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
{
const struct net *net = sock_net(sk);
struct tcp_sock *tp = tcp_sk(sk);
u32 delivered;
delivered = tp->delivered - prior_delivered;
NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
if (flag & FLAG_ECE) {
tp->delivered_ce += delivered;
NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
}
return delivered;
}
/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_sacktag_state sack_state;
struct rate_sample rs = { .prior_delivered = 0 };
u32 prior_snd_una = tp->snd_una;
bool is_sack_reneg = tp->is_sack_reneg;
u32 ack_seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
int num_dupack = 0;
int prior_packets = tp->packets_out;
u32 delivered = tp->delivered;
u32 lost = tp->lost;
int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
u32 prior_fack;
sack_state.first_sackt = 0;
sack_state.rate = &rs;
/* We very likely will need to access rtx queue. */
prefetch(sk->tcp_rtx_queue.rb_node);
/* If the ack is older than previous acks
* then we can probably ignore it.
*/
if (before(ack, prior_snd_una)) {
/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
if (before(ack, prior_snd_una - tp->max_window)) {
if (!(flag & FLAG_NO_CHALLENGE_ACK))
tcp_send_challenge_ack(sk, skb);
return -1;
}
goto old_ack;
}
/* If the ack includes data we haven't sent yet, discard
* this segment (RFC793 Section 3.9).
*/
if (after(ack, tp->snd_nxt))
return -1;
if (after(ack, prior_snd_una)) {
flag |= FLAG_SND_UNA_ADVANCED;
icsk->icsk_retransmits = 0;
#if IS_ENABLED(CONFIG_TLS_DEVICE)
if (static_branch_unlikely(&clean_acked_data_enabled.key))
if (icsk->icsk_clean_acked)
icsk->icsk_clean_acked(sk, ack);
#endif
}
prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
rs.prior_in_flight = tcp_packets_in_flight(tp);
/* ts_recent update must be made after we are sure that the packet
* is in window.
*/
if (flag & FLAG_UPDATE_TS_RECENT)
tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
FLAG_SND_UNA_ADVANCED) {
/* Window is constant, pure forward advance.
* No more checks are required.
* Note, we use the fact that SND.UNA>=SND.WL2.
*/
tcp_update_wl(tp, ack_seq);
tcp_snd_una_update(tp, ack);
flag |= FLAG_WIN_UPDATE;
tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
} else {
u32 ack_ev_flags = CA_ACK_SLOWPATH;
if (ack_seq != TCP_SKB_CB(skb)->end_seq)
flag |= FLAG_DATA;
else
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
if (TCP_SKB_CB(skb)->sacked)
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
&sack_state);
if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
flag |= FLAG_ECE;
ack_ev_flags |= CA_ACK_ECE;
}
if (flag & FLAG_WIN_UPDATE)
ack_ev_flags |= CA_ACK_WIN_UPDATE;
tcp_in_ack_event(sk, ack_ev_flags);
}
/* We passed data and got it acked, remove any soft error
* log. Something worked...
*/
sk->sk_err_soft = 0;
icsk->icsk_probes_out = 0;
tp->rcv_tstamp = tcp_jiffies32;
if (!prior_packets)
goto no_queue;
/* See if we can take anything off of the retransmit queue. */
flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state);
tcp_rack_update_reo_wnd(sk, &rs);
if (tp->tlp_high_seq)
tcp_process_tlp_ack(sk, ack, flag);
/* If needed, reset TLP/RTO timer; RACK may later override this. */
if (flag & FLAG_SET_XMIT_TIMER)
tcp_set_xmit_timer(sk);
if (tcp_ack_is_dubious(sk, flag)) {
if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) {
num_dupack = 1;
/* Consider if pure acks were aggregated in tcp_add_backlog() */
if (!(flag & FLAG_DATA))
num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
}
tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
}
if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
sk_dst_confirm(sk);
delivered = tcp_newly_delivered(sk, delivered, flag);
lost = tp->lost - lost; /* freshly marked lost */
rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
tcp_xmit_recovery(sk, rexmit);
return 1;
no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK) {
tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
tcp_newly_delivered(sk, delivered, flag);
}
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
* it needs to be for normal retransmission.
*/
tcp_ack_probe(sk);
if (tp->tlp_high_seq)
tcp_process_tlp_ack(sk, ack, flag);
return 1;
old_ack:
/* If data was SACKed, tag it and see if we should send more data.
* If data was DSACKed, see if we can undo a cwnd reduction.
*/
if (TCP_SKB_CB(skb)->sacked) {
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
&sack_state);
tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
&rexmit);
tcp_newly_delivered(sk, delivered, flag);
tcp_xmit_recovery(sk, rexmit);
}
return 0;
}
static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
bool syn, struct tcp_fastopen_cookie *foc,
bool exp_opt)
{
/* Valid only in SYN or SYN-ACK with an even length. */
if (!foc || !syn || len < 0 || (len & 1))
return;
if (len >= TCP_FASTOPEN_COOKIE_MIN &&
len <= TCP_FASTOPEN_COOKIE_MAX)
memcpy(foc->val, cookie, len);
else if (len != 0)
len = -1;
foc->len = len;
foc->exp = exp_opt;
}
static void smc_parse_options(const struct tcphdr *th,
struct tcp_options_received *opt_rx,
const unsigned char *ptr,
int opsize)
{
#if IS_ENABLED(CONFIG_SMC)
if (static_branch_unlikely(&tcp_have_smc)) {
if (th->syn && !(opsize & 1) &&
opsize >= TCPOLEN_EXP_SMC_BASE &&
get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC)
opt_rx->smc_ok = 1;
}
#endif
}
/* Look for tcp options. Normally only called on SYN and SYNACK packets.
* But, this can also be called on packets in the established flow when
* the fast version below fails.
*/
void tcp_parse_options(const struct net *net,
const struct sk_buff *skb,
struct tcp_options_received *opt_rx, int estab,
struct tcp_fastopen_cookie *foc)
{
const unsigned char *ptr;
const struct tcphdr *th = tcp_hdr(skb);
int length = (th->doff * 4) - sizeof(struct tcphdr);
ptr = (const unsigned char *)(th + 1);
opt_rx->saw_tstamp = 0;
while (length > 0) {
int opcode = *ptr++;
int opsize;
switch (opcode) {
case TCPOPT_EOL:
return;
case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
length--;
continue;
default:
if (length < 2)
return;
opsize = *ptr++;
if (opsize < 2) /* "silly options" */
return;
if (opsize > length)
return; /* don't parse partial options */
switch (opcode) {
case TCPOPT_MSS:
if (opsize == TCPOLEN_MSS && th->syn && !estab) {
u16 in_mss = get_unaligned_be16(ptr);
if (in_mss) {
if (opt_rx->user_mss &&
opt_rx->user_mss < in_mss)
in_mss = opt_rx->user_mss;
opt_rx->mss_clamp = in_mss;
}
}
break;
case TCPOPT_WINDOW:
if (opsize == TCPOLEN_WINDOW && th->syn &&
!estab && net->ipv4.sysctl_tcp_window_scaling) {
__u8 snd_wscale = *(__u8 *)ptr;
opt_rx->wscale_ok = 1;
if (snd_wscale > TCP_MAX_WSCALE) {
net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
__func__,
snd_wscale,
TCP_MAX_WSCALE);
snd_wscale = TCP_MAX_WSCALE;
}
opt_rx->snd_wscale = snd_wscale;
}
break;
case TCPOPT_TIMESTAMP:
if ((opsize == TCPOLEN_TIMESTAMP) &&
((estab && opt_rx->tstamp_ok) ||
(!estab && net->ipv4.sysctl_tcp_timestamps))) {
opt_rx->saw_tstamp = 1;
opt_rx->rcv_tsval = get_unaligned_be32(ptr);
opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
}
break;
case TCPOPT_SACK_PERM:
if (opsize == TCPOLEN_SACK_PERM && th->syn &&
!estab && net->ipv4.sysctl_tcp_sack) {
opt_rx->sack_ok = TCP_SACK_SEEN;
tcp_sack_reset(opt_rx);
}
break;
case TCPOPT_SACK:
if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
!((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
opt_rx->sack_ok) {
TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
}
break;
#ifdef CONFIG_TCP_MD5SIG
case TCPOPT_MD5SIG:
/*
* The MD5 Hash has already been
* checked (see tcp_v{4,6}_do_rcv()).
*/
break;
#endif
case TCPOPT_FASTOPEN:
tcp_parse_fastopen_option(
opsize - TCPOLEN_FASTOPEN_BASE,
ptr, th->syn, foc, false);
break;
case TCPOPT_EXP:
/* Fast Open option shares code 254 using a
* 16 bits magic number.
*/
if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
get_unaligned_be16(ptr) ==
TCPOPT_FASTOPEN_MAGIC)
tcp_parse_fastopen_option(opsize -
TCPOLEN_EXP_FASTOPEN_BASE,
ptr + 2, th->syn, foc, true);
else
smc_parse_options(th, opt_rx, ptr,
opsize);
break;
}
ptr += opsize-2;
length -= opsize;
}
}
}
EXPORT_SYMBOL(tcp_parse_options);
static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
{
const __be32 *ptr = (const __be32 *)(th + 1);
if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
| (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
tp->rx_opt.saw_tstamp = 1;
++ptr;
tp->rx_opt.rcv_tsval = ntohl(*ptr);
++ptr;
if (*ptr)
tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
else
tp->rx_opt.rcv_tsecr = 0;
return true;
}
return false;
}
/* Fast parse options. This hopes to only see timestamps.
* If it is wrong it falls back on tcp_parse_options().
*/
static bool tcp_fast_parse_options(const struct net *net,
const struct sk_buff *skb,
const struct tcphdr *th, struct tcp_sock *tp)
{
/* In the spirit of fast parsing, compare doff directly to constant
* values. Because equality is used, short doff can be ignored here.
*/
if (th->doff == (sizeof(*th) / 4)) {
tp->rx_opt.saw_tstamp = 0;
return false;
} else if (tp->rx_opt.tstamp_ok &&
th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
if (tcp_parse_aligned_timestamp(tp, th))
return true;
}
tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
tp->rx_opt.rcv_tsecr -= tp->tsoffset;
return true;
}
#ifdef CONFIG_TCP_MD5SIG
/*
* Parse MD5 Signature option
*/
const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
{
int length = (th->doff << 2) - sizeof(*th);
const u8 *ptr = (const u8 *)(th + 1);
/* If not enough data remaining, we can short cut */
while (length >= TCPOLEN_MD5SIG) {
int opcode = *ptr++;
int opsize;
switch (opcode) {
case TCPOPT_EOL:
return NULL;
case TCPOPT_NOP:
length--;
continue;
default:
opsize = *ptr++;
if (opsize < 2 || opsize > length)
return NULL;
if (opcode == TCPOPT_MD5SIG)
return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
}
ptr += opsize - 2;
length -= opsize;
}
return NULL;
}
EXPORT_SYMBOL(tcp_parse_md5sig_option);
#endif
/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
*
* It is not fatal. If this ACK does _not_ change critical state (seqs, window)
* it can pass through stack. So, the following predicate verifies that
* this segment is not used for anything but congestion avoidance or
* fast retransmit. Moreover, we even are able to eliminate most of such
* second order effects, if we apply some small "replay" window (~RTO)
* to timestamp space.
*
* All these measures still do not guarantee that we reject wrapped ACKs
* on networks with high bandwidth, when sequence space is recycled fastly,
* but it guarantees that such events will be very rare and do not affect
* connection seriously. This doesn't look nice, but alas, PAWS is really
* buggy extension.
*
* [ Later note. Even worse! It is buggy for segments _with_ data. RFC
* states that events when retransmit arrives after original data are rare.
* It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
* the biggest problem on large power networks even with minor reordering.
* OK, let's give it small replay window. If peer clock is even 1hz, it is safe
* up to bandwidth of 18Gigabit/sec. 8) ]
*/
static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct tcphdr *th = tcp_hdr(skb);
u32 seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
return (/* 1. Pure ACK with correct sequence number. */
(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
/* 2. ... and duplicate ACK. */
ack == tp->snd_una &&
/* 3. ... and does not update window. */
!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
/* 4. ... and sits in replay window. */
(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
}
static inline bool tcp_paws_discard(const struct sock *sk,
const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
!tcp_disordered_ack(sk, skb);
}
/* Check segment sequence number for validity.
*
* Segment controls are considered valid, if the segment
* fits to the window after truncation to the window. Acceptability
* of data (and SYN, FIN, of course) is checked separately.
* See tcp_data_queue(), for example.
*
* Also, controls (RST is main one) are accepted using RCV.WUP instead
* of RCV.NXT. Peer still did not advance his SND.UNA when we
* delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
* (borrowed from freebsd)
*/
static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
{
return !before(end_seq, tp->rcv_wup) &&
!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
}
/* When we get a reset we do this. */
void tcp_reset(struct sock *sk)
{
trace_tcp_receive_reset(sk);
/* We want the right error as BSD sees it (and indeed as we do). */
switch (sk->sk_state) {
case TCP_SYN_SENT:
sk->sk_err = ECONNREFUSED;
break;
case TCP_CLOSE_WAIT:
sk->sk_err = EPIPE;
break;
case TCP_CLOSE:
return;
default:
sk->sk_err = ECONNRESET;
}
/* This barrier is coupled with smp_rmb() in tcp_poll() */
smp_wmb();
tcp_write_queue_purge(sk);
tcp_done(sk);
if (!sock_flag(sk, SOCK_DEAD))
sk->sk_error_report(sk);
}
/*
* Process the FIN bit. This now behaves as it is supposed to work
* and the FIN takes effect when it is validly part of sequence
* space. Not before when we get holes.
*
* If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
* (and thence onto LAST-ACK and finally, CLOSE, we never enter
* TIME-WAIT)
*
* If we are in FINWAIT-1, a received FIN indicates simultaneous
* close and we go into CLOSING (and later onto TIME-WAIT)
*
* If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
*/
void tcp_fin(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
inet_csk_schedule_ack(sk);
sk->sk_shutdown |= RCV_SHUTDOWN;
sock_set_flag(sk, SOCK_DONE);
switch (sk->sk_state) {
case TCP_SYN_RECV:
case TCP_ESTABLISHED:
/* Move to CLOSE_WAIT */
tcp_set_state(sk, TCP_CLOSE_WAIT);
inet_csk_enter_pingpong_mode(sk);
break;
case TCP_CLOSE_WAIT:
case TCP_CLOSING:
/* Received a retransmission of the FIN, do
* nothing.
*/
break;
case TCP_LAST_ACK:
/* RFC793: Remain in the LAST-ACK state. */
break;
case TCP_FIN_WAIT1:
/* This case occurs when a simultaneous close
* happens, we must ack the received FIN and
* enter the CLOSING state.
*/
tcp_send_ack(sk);
tcp_set_state(sk, TCP_CLOSING);
break;
case TCP_FIN_WAIT2:
/* Received a FIN -- send ACK and enter TIME_WAIT. */
tcp_send_ack(sk);
tcp_time_wait(sk, TCP_TIME_WAIT, 0);
break;
default:
/* Only TCP_LISTEN and TCP_CLOSE are left, in these
* cases we should never reach this piece of code.
*/
pr_err("%s: Impossible, sk->sk_state=%d\n",
__func__, sk->sk_state);
break;
}
/* It _is_ possible, that we have something out-of-order _after_ FIN.
* Probably, we should reset in this case. For now drop them.
*/
skb_rbtree_purge(&tp->out_of_order_queue);
if (tcp_is_sack(tp))
tcp_sack_reset(&tp->rx_opt);
sk_mem_reclaim(sk);
if (!sock_flag(sk, SOCK_DEAD)) {
sk->sk_state_change(sk);
/* Do not send POLL_HUP for half duplex close. */
if (sk->sk_shutdown == SHUTDOWN_MASK ||
sk->sk_state == TCP_CLOSE)
sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
else
sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
}
}
static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
u32 end_seq)
{
if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
if (before(seq, sp->start_seq))
sp->start_seq = seq;
if (after(end_seq, sp->end_seq))
sp->end_seq = end_seq;
return true;
}
return false;
}
static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
int mib_idx;
if (before(seq, tp->rcv_nxt))
mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
else
mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
NET_INC_STATS(sock_net(sk), mib_idx);
tp->rx_opt.dsack = 1;
tp->duplicate_sack[0].start_seq = seq;
tp->duplicate_sack[0].end_seq = end_seq;
}
}
static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tp->rx_opt.dsack)
tcp_dsack_set(sk, seq, end_seq);
else
tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
}
static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
{
/* When the ACK path fails or drops most ACKs, the sender would
* timeout and spuriously retransmit the same segment repeatedly.
* The receiver remembers and reflects via DSACKs. Leverage the
* DSACK state and change the txhash to re-route speculatively.
*/
if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq)
sk_rethink_txhash(sk);
}
static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
u32 end_seq = TCP_SKB_CB(skb)->end_seq;
tcp_rcv_spurious_retrans(sk, skb);
if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
end_seq = tp->rcv_nxt;
tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
}
}
tcp_send_ack(sk);
}
/* These routines update the SACK block as out-of-order packets arrive or
* in-order packets close up the sequence space.
*/
static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
{
int this_sack;
struct tcp_sack_block *sp = &tp->selective_acks[0];
struct tcp_sack_block *swalk = sp + 1;
/* See if the recent change to the first SACK eats into
* or hits the sequence space of other SACK blocks, if so coalesce.
*/
for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
int i;
/* Zap SWALK, by moving every further SACK up by one slot.
* Decrease num_sacks.
*/
tp->rx_opt.num_sacks--;
for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
sp[i] = sp[i + 1];
continue;
}
this_sack++, swalk++;
}
}
static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_sack_block *sp = &tp->selective_acks[0];
int cur_sacks = tp->rx_opt.num_sacks;
int this_sack;
if (!cur_sacks)
goto new_sack;
for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
if (tcp_sack_extend(sp, seq, end_seq)) {
/* Rotate this_sack to the first one. */
for (; this_sack > 0; this_sack--, sp--)
swap(*sp, *(sp - 1));
if (cur_sacks > 1)
tcp_sack_maybe_coalesce(tp);
return;
}
}
/* Could not find an adjacent existing SACK, build a new one,
* put it at the front, and shift everyone else down. We
* always know there is at least one SACK present already here.
*
* If the sack array is full, forget about the last one.
*/
if (this_sack >= TCP_NUM_SACKS) {
if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
tcp_send_ack(sk);
this_sack--;
tp->rx_opt.num_sacks--;
sp--;
}
for (; this_sack > 0; this_sack--, sp--)
*sp = *(sp - 1);
new_sack:
/* Build the new head SACK, and we're done. */
sp->start_seq = seq;
sp->end_seq = end_seq;
tp->rx_opt.num_sacks++;
}
/* RCV.NXT advances, some SACKs should be eaten. */
static void tcp_sack_remove(struct tcp_sock *tp)
{
struct tcp_sack_block *sp = &tp->selective_acks[0];
int num_sacks = tp->rx_opt.num_sacks;
int this_sack;
/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
tp->rx_opt.num_sacks = 0;
return;
}
for (this_sack = 0; this_sack < num_sacks;) {
/* Check if the start of the sack is covered by RCV.NXT. */
if (!before(tp->rcv_nxt, sp->start_seq)) {
int i;
/* RCV.NXT must cover all the block! */
WARN_ON(before(tp->rcv_nxt, sp->end_seq));
/* Zap this SACK, by moving forward any other SACKS. */
for (i = this_sack+1; i < num_sacks; i++)
tp->selective_acks[i-1] = tp->selective_acks[i];
num_sacks--;
continue;
}
this_sack++;
sp++;
}
tp->rx_opt.num_sacks = num_sacks;
}
/**
* tcp_try_coalesce - try to merge skb to prior one
* @sk: socket
* @dest: destination queue
* @to: prior buffer
* @from: buffer to add in queue
* @fragstolen: pointer to boolean
*
* Before queueing skb @from after @to, try to merge them
* to reduce overall memory use and queue lengths, if cost is small.
* Packets in ofo or receive queues can stay a long time.
* Better try to coalesce them right now to avoid future collapses.
* Returns true if caller should free @from instead of queueing it
*/
static bool tcp_try_coalesce(struct sock *sk,
struct sk_buff *to,
struct sk_buff *from,
bool *fragstolen)
{
int delta;
*fragstolen = false;
/* Its possible this segment overlaps with prior segment in queue */
if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
return false;
#ifdef CONFIG_TLS_DEVICE
if (from->decrypted != to->decrypted)
return false;
#endif
if (!skb_try_coalesce(to, from, fragstolen, &delta))
return false;
atomic_add(delta, &sk->sk_rmem_alloc);
sk_mem_charge(sk, delta);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
if (TCP_SKB_CB(from)->has_rxtstamp) {
TCP_SKB_CB(to)->has_rxtstamp = true;
to->tstamp = from->tstamp;
skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
}
return true;
}
static bool tcp_ooo_try_coalesce(struct sock *sk,
struct sk_buff *to,
struct sk_buff *from,
bool *fragstolen)
{
bool res = tcp_try_coalesce(sk, to, from, fragstolen);
/* In case tcp_drop() is called later, update to->gso_segs */
if (res) {
u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
max_t(u16, 1, skb_shinfo(from)->gso_segs);
skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
}
return res;
}
static void tcp_drop(struct sock *sk, struct sk_buff *skb)
{
sk_drops_add(sk, skb);
__kfree_skb(skb);
}
/* This one checks to see if we can put data from the
* out_of_order queue into the receive_queue.
*/
static void tcp_ofo_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
__u32 dsack_high = tp->rcv_nxt;
bool fin, fragstolen, eaten;
struct sk_buff *skb, *tail;
struct rb_node *p;
p = rb_first(&tp->out_of_order_queue);
while (p) {
skb = rb_to_skb(p);
if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
break;
if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
__u32 dsack = dsack_high;
if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
dsack_high = TCP_SKB_CB(skb)->end_seq;
tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
}
p = rb_next(p);
rb_erase(&skb->rbnode, &tp->out_of_order_queue);
if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
tcp_drop(sk, skb);
continue;
}
tail = skb_peek_tail(&sk->sk_receive_queue);
eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
if (!eaten)
__skb_queue_tail(&sk->sk_receive_queue, skb);
else
kfree_skb_partial(skb, fragstolen);
if (unlikely(fin)) {
tcp_fin(sk);
/* tcp_fin() purges tp->out_of_order_queue,
* so we must end this loop right now.
*/
break;
}
}
}
static bool tcp_prune_ofo_queue(struct sock *sk);
static int tcp_prune_queue(struct sock *sk);
static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
unsigned int size)
{
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
!sk_rmem_schedule(sk, skb, size)) {
if (tcp_prune_queue(sk) < 0)
return -1;
while (!sk_rmem_schedule(sk, skb, size)) {
if (!tcp_prune_ofo_queue(sk))
return -1;
}
}
return 0;
}
static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct rb_node **p, *parent;
struct sk_buff *skb1;
u32 seq, end_seq;
bool fragstolen;
tcp_ecn_check_ce(sk, skb);
if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
tcp_drop(sk, skb);
return;
}
/* Disable header prediction. */
tp->pred_flags = 0;
inet_csk_schedule_ack(sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
seq = TCP_SKB_CB(skb)->seq;
end_seq = TCP_SKB_CB(skb)->end_seq;
p = &tp->out_of_order_queue.rb_node;
if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
/* Initial out of order segment, build 1 SACK. */
if (tcp_is_sack(tp)) {
tp->rx_opt.num_sacks = 1;
tp->selective_acks[0].start_seq = seq;
tp->selective_acks[0].end_seq = end_seq;
}
rb_link_node(&skb->rbnode, NULL, p);
rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
tp->ooo_last_skb = skb;
goto end;
}
/* In the typical case, we are adding an skb to the end of the list.
* Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
*/
if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
skb, &fragstolen)) {
coalesce_done:
tcp_grow_window(sk, skb);
kfree_skb_partial(skb, fragstolen);
skb = NULL;
goto add_sack;
}
/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
parent = &tp->ooo_last_skb->rbnode;
p = &parent->rb_right;
goto insert;
}
/* Find place to insert this segment. Handle overlaps on the way. */
parent = NULL;
while (*p) {
parent = *p;
skb1 = rb_to_skb(parent);
if (before(seq, TCP_SKB_CB(skb1)->seq)) {
p = &parent->rb_left;
continue;
}
if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
/* All the bits are present. Drop. */
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPOFOMERGE);
tcp_drop(sk, skb);
skb = NULL;
tcp_dsack_set(sk, seq, end_seq);
goto add_sack;
}
if (after(seq, TCP_SKB_CB(skb1)->seq)) {
/* Partial overlap. */
tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
} else {
/* skb's seq == skb1's seq and skb covers skb1.
* Replace skb1 with skb.
*/
rb_replace_node(&skb1->rbnode, &skb->rbnode,
&tp->out_of_order_queue);
tcp_dsack_extend(sk,
TCP_SKB_CB(skb1)->seq,
TCP_SKB_CB(skb1)->end_seq);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPOFOMERGE);
tcp_drop(sk, skb1);
goto merge_right;
}
} else if (tcp_ooo_try_coalesce(sk, skb1,
skb, &fragstolen)) {
goto coalesce_done;
}
p = &parent->rb_right;
}
insert:
/* Insert segment into RB tree. */
rb_link_node(&skb->rbnode, parent, p);
rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
merge_right:
/* Remove other segments covered by skb. */
while ((skb1 = skb_rb_next(skb)) != NULL) {
if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
break;
if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
end_seq);
break;
}
rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
TCP_SKB_CB(skb1)->end_seq);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
tcp_drop(sk, skb1);
}
/* If there is no skb after us, we are the last_skb ! */
if (!skb1)
tp->ooo_last_skb = skb;
add_sack:
if (tcp_is_sack(tp))
tcp_sack_new_ofo_skb(sk, seq, end_seq);
end:
if (skb) {
tcp_grow_window(sk, skb);
skb_condense(skb);
skb_set_owner_r(skb, sk);
}
}
static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
bool *fragstolen)
{
int eaten;
struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
eaten = (tail &&
tcp_try_coalesce(sk, tail,
skb, fragstolen)) ? 1 : 0;
tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
if (!eaten) {
__skb_queue_tail(&sk->sk_receive_queue, skb);
skb_set_owner_r(skb, sk);
}
return eaten;
}
int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
{
struct sk_buff *skb;
int err = -ENOMEM;
int data_len = 0;
bool fragstolen;
if (size == 0)
return 0;
if (size > PAGE_SIZE) {
int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
data_len = npages << PAGE_SHIFT;
size = data_len + (size & ~PAGE_MASK);
}
skb = alloc_skb_with_frags(size - data_len, data_len,
PAGE_ALLOC_COSTLY_ORDER,
&err, sk->sk_allocation);
if (!skb)
goto err;
skb_put(skb, size - data_len);
skb->data_len = data_len;
skb->len = size;
if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
goto err_free;
}
err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
if (err)
goto err_free;
TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
if (tcp_queue_rcv(sk, skb, &fragstolen)) {
WARN_ON_ONCE(fragstolen); /* should not happen */
__kfree_skb(skb);
}
return size;
err_free:
kfree_skb(skb);
err:
return err;
}
void tcp_data_ready(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
int avail = tp->rcv_nxt - tp->copied_seq;
if (avail < sk->sk_rcvlowat && !sock_flag(sk, SOCK_DONE))
return;
sk->sk_data_ready(sk);
}
static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
bool fragstolen;
int eaten;
if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
__kfree_skb(skb);
return;
}
skb_dst_drop(skb);
__skb_pull(skb, tcp_hdr(skb)->doff * 4);
tcp_ecn_accept_cwr(sk, skb);
tp->rx_opt.dsack = 0;
/* Queue data for delivery to the user.
* Packets in sequence go to the receive queue.
* Out of sequence packets to the out_of_order_queue.
*/
if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
if (tcp_receive_window(tp) == 0) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
goto out_of_window;
}
/* Ok. In sequence. In window. */
queue_and_out:
if (skb_queue_len(&sk->sk_receive_queue) == 0)
sk_forced_mem_schedule(sk, skb->truesize);
else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
goto drop;
}
eaten = tcp_queue_rcv(sk, skb, &fragstolen);
if (skb->len)
tcp_event_data_recv(sk, skb);
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
tcp_fin(sk);
if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
tcp_ofo_queue(sk);
/* RFC5681. 4.2. SHOULD send immediate ACK, when
* gap in queue is filled.
*/
if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
}
if (tp->rx_opt.num_sacks)
tcp_sack_remove(tp);
tcp_fast_path_check(sk);
if (eaten > 0)
kfree_skb_partial(skb, fragstolen);
if (!sock_flag(sk, SOCK_DEAD))
tcp_data_ready(sk);
return;
}
if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
tcp_rcv_spurious_retrans(sk, skb);
/* A retransmit, 2nd most common case. Force an immediate ack. */
NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
out_of_window:
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
inet_csk_schedule_ack(sk);
drop:
tcp_drop(sk, skb);
return;
}
/* Out of window. F.e. zero window probe. */
if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
goto out_of_window;
if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
/* Partial packet, seq < rcv_next < end_seq */
tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
/* If window is closed, drop tail of packet. But after
* remembering D-SACK for its head made in previous line.
*/
if (!tcp_receive_window(tp)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
goto out_of_window;
}
goto queue_and_out;
}
tcp_data_queue_ofo(sk, skb);
}
static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
{
if (list)
return !skb_queue_is_last(list, skb) ? skb->next : NULL;
return skb_rb_next(skb);
}
static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
struct sk_buff_head *list,
struct rb_root *root)
{
struct sk_buff *next = tcp_skb_next(skb, list);
if (list)
__skb_unlink(skb, list);
else
rb_erase(&skb->rbnode, root);
__kfree_skb(skb);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
return next;
}
/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
{
struct rb_node **p = &root->rb_node;
struct rb_node *parent = NULL;
struct sk_buff *skb1;
while (*p) {
parent = *p;
skb1 = rb_to_skb(parent);
if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
p = &parent->rb_left;
else
p = &parent->rb_right;
}
rb_link_node(&skb->rbnode, parent, p);
rb_insert_color(&skb->rbnode, root);
}
/* Collapse contiguous sequence of skbs head..tail with
* sequence numbers start..end.
*
* If tail is NULL, this means until the end of the queue.
*
* Segments with FIN/SYN are not collapsed (only because this
* simplifies code)
*/
static void
tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
{
struct sk_buff *skb = head, *n;
struct sk_buff_head tmp;
bool end_of_skbs;
/* First, check that queue is collapsible and find
* the point where collapsing can be useful.
*/
restart:
for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
n = tcp_skb_next(skb, list);
/* No new bits? It is possible on ofo queue. */
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
skb = tcp_collapse_one(sk, skb, list, root);
if (!skb)
break;
goto restart;
}
/* The first skb to collapse is:
* - not SYN/FIN and
* - bloated or contains data before "start" or
* overlaps to the next one.
*/
if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
(tcp_win_from_space(sk, skb->truesize) > skb->len ||
before(TCP_SKB_CB(skb)->seq, start))) {
end_of_skbs = false;
break;
}
if (n && n != tail &&
TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
end_of_skbs = false;
break;
}
/* Decided to skip this, advance start seq. */
start = TCP_SKB_CB(skb)->end_seq;
}
if (end_of_skbs ||
(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
return;
__skb_queue_head_init(&tmp);
while (before(start, end)) {
int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
struct sk_buff *nskb;
nskb = alloc_skb(copy, GFP_ATOMIC);
if (!nskb)
break;
memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
#ifdef CONFIG_TLS_DEVICE
nskb->decrypted = skb->decrypted;
#endif
TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
if (list)
__skb_queue_before(list, skb, nskb);
else
__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
skb_set_owner_r(nskb, sk);
/* Copy data, releasing collapsed skbs. */
while (copy > 0) {
int offset = start - TCP_SKB_CB(skb)->seq;
int size = TCP_SKB_CB(skb)->end_seq - start;
BUG_ON(offset < 0);
if (size > 0) {
size = min(copy, size);
if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
BUG();
TCP_SKB_CB(nskb)->end_seq += size;
copy -= size;
start += size;
}
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
skb = tcp_collapse_one(sk, skb, list, root);
if (!skb ||
skb == tail ||
(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
goto end;
#ifdef CONFIG_TLS_DEVICE
if (skb->decrypted != nskb->decrypted)
goto end;
#endif
}
}
}
end:
skb_queue_walk_safe(&tmp, skb, n)
tcp_rbtree_insert(root, skb);
}
/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
* and tcp_collapse() them until all the queue is collapsed.
*/
static void tcp_collapse_ofo_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 range_truesize, sum_tiny = 0;
struct sk_buff *skb, *head;
u32 start, end;
skb = skb_rb_first(&tp->out_of_order_queue);
new_range:
if (!skb) {
tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
return;
}
start = TCP_SKB_CB(skb)->seq;
end = TCP_SKB_CB(skb)->end_seq;
range_truesize = skb->truesize;
for (head = skb;;) {
skb = skb_rb_next(skb);
/* Range is terminated when we see a gap or when
* we are at the queue end.
*/
if (!skb ||
after(TCP_SKB_CB(skb)->seq, end) ||
before(TCP_SKB_CB(skb)->end_seq, start)) {
/* Do not attempt collapsing tiny skbs */
if (range_truesize != head->truesize ||
end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) {
tcp_collapse(sk, NULL, &tp->out_of_order_queue,
head, skb, start, end);
} else {
sum_tiny += range_truesize;
if (sum_tiny > sk->sk_rcvbuf >> 3)
return;
}
goto new_range;
}
range_truesize += skb->truesize;
if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
start = TCP_SKB_CB(skb)->seq;
if (after(TCP_SKB_CB(skb)->end_seq, end))
end = TCP_SKB_CB(skb)->end_seq;
}
}
/*
* Clean the out-of-order queue to make room.
* We drop high sequences packets to :
* 1) Let a chance for holes to be filled.
* 2) not add too big latencies if thousands of packets sit there.
* (But if application shrinks SO_RCVBUF, we could still end up
* freeing whole queue here)
* 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
*
* Return true if queue has shrunk.
*/
static bool tcp_prune_ofo_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct rb_node *node, *prev;
int goal;
if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
return false;
NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
goal = sk->sk_rcvbuf >> 3;
node = &tp->ooo_last_skb->rbnode;
do {
prev = rb_prev(node);
rb_erase(node, &tp->out_of_order_queue);
goal -= rb_to_skb(node)->truesize;
tcp_drop(sk, rb_to_skb(node));
if (!prev || goal <= 0) {
sk_mem_reclaim(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
!tcp_under_memory_pressure(sk))
break;
goal = sk->sk_rcvbuf >> 3;
}
node = prev;
} while (node);
tp->ooo_last_skb = rb_to_skb(prev);
/* Reset SACK state. A conforming SACK implementation will
* do the same at a timeout based retransmit. When a connection
* is in a sad state like this, we care only about integrity
* of the connection not performance.
*/
if (tp->rx_opt.sack_ok)
tcp_sack_reset(&tp->rx_opt);
return true;
}
/* Reduce allocated memory if we can, trying to get
* the socket within its memory limits again.
*
* Return less than zero if we should start dropping frames
* until the socket owning process reads some of the data
* to stabilize the situation.
*/
static int tcp_prune_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
tcp_clamp_window(sk);
else if (tcp_under_memory_pressure(sk))
tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
return 0;
tcp_collapse_ofo_queue(sk);
if (!skb_queue_empty(&sk->sk_receive_queue))
tcp_collapse(sk, &sk->sk_receive_queue, NULL,
skb_peek(&sk->sk_receive_queue),
NULL,
tp->copied_seq, tp->rcv_nxt);
sk_mem_reclaim(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
return 0;
/* Collapsing did not help, destructive actions follow.
* This must not ever occur. */
tcp_prune_ofo_queue(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
return 0;
/* If we are really being abused, tell the caller to silently
* drop receive data on the floor. It will get retransmitted
* and hopefully then we'll have sufficient space.
*/
NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
/* Massive buffer overcommit. */
tp->pred_flags = 0;
return -1;
}
static bool tcp_should_expand_sndbuf(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* If the user specified a specific send buffer setting, do
* not modify it.
*/
if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
return false;
/* If we are under global TCP memory pressure, do not expand. */
if (tcp_under_memory_pressure(sk))
return false;
/* If we are under soft global TCP memory pressure, do not expand. */
if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
return false;
/* If we filled the congestion window, do not expand. */
if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
return false;
return true;
}
/* When incoming ACK allowed to free some skb from write_queue,
* we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
* on the exit from tcp input handler.
*
* PROBLEM: sndbuf expansion does not work well with largesend.
*/
static void tcp_new_space(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_should_expand_sndbuf(sk)) {
tcp_sndbuf_expand(sk);
tp->snd_cwnd_stamp = tcp_jiffies32;
}
sk->sk_write_space(sk);
}
static void tcp_check_space(struct sock *sk)
{
if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
/* pairs with tcp_poll() */
smp_mb();
if (sk->sk_socket &&
test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
tcp_new_space(sk);
if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
}
}
}
static inline void tcp_data_snd_check(struct sock *sk)
{
tcp_push_pending_frames(sk);
tcp_check_space(sk);
}
/*
* Check if sending an ack is needed.
*/
static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
{
struct tcp_sock *tp = tcp_sk(sk);
unsigned long rtt, delay;
/* More than one full frame received... */
if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
/* ... and right edge of window advances far enough.
* (tcp_recvmsg() will send ACK otherwise).
* If application uses SO_RCVLOWAT, we want send ack now if
* we have not received enough bytes to satisfy the condition.
*/
(tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
__tcp_select_window(sk) >= tp->rcv_wnd)) ||
/* We ACK each frame or... */
tcp_in_quickack_mode(sk) ||
/* Protocol state mandates a one-time immediate ACK */
inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
send_now:
tcp_send_ack(sk);
return;
}
if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
tcp_send_delayed_ack(sk);
return;
}
if (!tcp_is_sack(tp) ||
tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
goto send_now;
if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
tp->compressed_ack - TCP_FASTRETRANS_THRESH);
tp->compressed_ack = 0;
}
if (++tp->compressed_ack <= TCP_FASTRETRANS_THRESH)
goto send_now;
if (hrtimer_is_queued(&tp->compressed_ack_timer))
return;
/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
rtt = tp->rcv_rtt_est.rtt_us;
if (tp->srtt_us && tp->srtt_us < rtt)
rtt = tp->srtt_us;
delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
rtt * (NSEC_PER_USEC >> 3)/20);
sock_hold(sk);
hrtimer_start(&tp->compressed_ack_timer, ns_to_ktime(delay),
HRTIMER_MODE_REL_PINNED_SOFT);
}
static inline void tcp_ack_snd_check(struct sock *sk)
{
if (!inet_csk_ack_scheduled(sk)) {
/* We sent a data segment already. */
return;
}
__tcp_ack_snd_check(sk, 1);
}
/*
* This routine is only called when we have urgent data
* signaled. Its the 'slow' part of tcp_urg. It could be
* moved inline now as tcp_urg is only called from one
* place. We handle URGent data wrong. We have to - as
* BSD still doesn't use the correction from RFC961.
* For 1003.1g we should support a new option TCP_STDURG to permit
* either form (or just set the sysctl tcp_stdurg).
*/
static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 ptr = ntohs(th->urg_ptr);
if (ptr && !sock_net(sk)->ipv4.sysctl_tcp_stdurg)
ptr--;
ptr += ntohl(th->seq);
/* Ignore urgent data that we've already seen and read. */
if (after(tp->copied_seq, ptr))
return;
/* Do not replay urg ptr.
*
* NOTE: interesting situation not covered by specs.
* Misbehaving sender may send urg ptr, pointing to segment,
* which we already have in ofo queue. We are not able to fetch
* such data and will stay in TCP_URG_NOTYET until will be eaten
* by recvmsg(). Seems, we are not obliged to handle such wicked
* situations. But it is worth to think about possibility of some
* DoSes using some hypothetical application level deadlock.
*/
if (before(ptr, tp->rcv_nxt))
return;
/* Do we already have a newer (or duplicate) urgent pointer? */
if (tp->urg_data && !after(ptr, tp->urg_seq))
return;
/* Tell the world about our new urgent pointer. */
sk_send_sigurg(sk);
/* We may be adding urgent data when the last byte read was
* urgent. To do this requires some care. We cannot just ignore
* tp->copied_seq since we would read the last urgent byte again
* as data, nor can we alter copied_seq until this data arrives
* or we break the semantics of SIOCATMARK (and thus sockatmark())
*
* NOTE. Double Dutch. Rendering to plain English: author of comment
* above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
* and expect that both A and B disappear from stream. This is _wrong_.
* Though this happens in BSD with high probability, this is occasional.
* Any application relying on this is buggy. Note also, that fix "works"
* only in this artificial test. Insert some normal data between A and B and we will
* decline of BSD again. Verdict: it is better to remove to trap
* buggy users.
*/
if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
!sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
tp->copied_seq++;
if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
__skb_unlink(skb, &sk->sk_receive_queue);
__kfree_skb(skb);
}
}
tp->urg_data = TCP_URG_NOTYET;
tp->urg_seq = ptr;
/* Disable header prediction. */
tp->pred_flags = 0;
}
/* This is the 'fast' part of urgent handling. */
static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Check if we get a new urgent pointer - normally not. */
if (th->urg)
tcp_check_urg(sk, th);
/* Do we wait for any urgent data? - normally not... */
if (tp->urg_data == TCP_URG_NOTYET) {
u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
th->syn;
/* Is the urgent pointer pointing into this packet? */
if (ptr < skb->len) {
u8 tmp;
if (skb_copy_bits(skb, ptr, &tmp, 1))
BUG();
tp->urg_data = TCP_URG_VALID | tmp;
if (!sock_flag(sk, SOCK_DEAD))
sk->sk_data_ready(sk);
}
}
}
/* Accept RST for rcv_nxt - 1 after a FIN.
* When tcp connections are abruptly terminated from Mac OSX (via ^C), a
* FIN is sent followed by a RST packet. The RST is sent with the same
* sequence number as the FIN, and thus according to RFC 5961 a challenge
* ACK should be sent. However, Mac OSX rate limits replies to challenge
* ACKs on the closed socket. In addition middleboxes can drop either the
* challenge ACK or a subsequent RST.
*/
static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
TCPF_CLOSING));
}
/* Does PAWS and seqno based validation of an incoming segment, flags will
* play significant role here.
*/
static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
const struct tcphdr *th, int syn_inerr)
{
struct tcp_sock *tp = tcp_sk(sk);
bool rst_seq_match = false;
/* RFC1323: H1. Apply PAWS check first. */
if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
tp->rx_opt.saw_tstamp &&
tcp_paws_discard(sk, skb)) {
if (!th->rst) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
if (!tcp_oow_rate_limited(sock_net(sk), skb,
LINUX_MIB_TCPACKSKIPPEDPAWS,
&tp->last_oow_ack_time))
tcp_send_dupack(sk, skb);
goto discard;
}
/* Reset is accepted even if it did not pass PAWS. */
}
/* Step 1: check sequence number */
if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
/* RFC793, page 37: "In all states except SYN-SENT, all reset
* (RST) segments are validated by checking their SEQ-fields."
* And page 69: "If an incoming segment is not acceptable,
* an acknowledgment should be sent in reply (unless the RST
* bit is set, if so drop the segment and return)".
*/
if (!th->rst) {
if (th->syn)
goto syn_challenge;
if (!tcp_oow_rate_limited(sock_net(sk), skb,
LINUX_MIB_TCPACKSKIPPEDSEQ,
&tp->last_oow_ack_time))
tcp_send_dupack(sk, skb);
} else if (tcp_reset_check(sk, skb)) {
tcp_reset(sk);
}
goto discard;
}
/* Step 2: check RST bit */
if (th->rst) {
/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
* FIN and SACK too if available):
* If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
* the right-most SACK block,
* then
* RESET the connection
* else
* Send a challenge ACK
*/
if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
tcp_reset_check(sk, skb)) {
rst_seq_match = true;
} else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
struct tcp_sack_block *sp = &tp->selective_acks[0];
int max_sack = sp[0].end_seq;
int this_sack;
for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
++this_sack) {
max_sack = after(sp[this_sack].end_seq,
max_sack) ?
sp[this_sack].end_seq : max_sack;
}
if (TCP_SKB_CB(skb)->seq == max_sack)
rst_seq_match = true;
}
if (rst_seq_match)
tcp_reset(sk);
else {
/* Disable TFO if RST is out-of-order
* and no data has been received
* for current active TFO socket
*/
if (tp->syn_fastopen && !tp->data_segs_in &&
sk->sk_state == TCP_ESTABLISHED)
tcp_fastopen_active_disable(sk);
tcp_send_challenge_ack(sk, skb);
}
goto discard;
}
/* step 3: check security and precedence [ignored] */
/* step 4: Check for a SYN
* RFC 5961 4.2 : Send a challenge ack
*/
if (th->syn) {
syn_challenge:
if (syn_inerr)
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
tcp_send_challenge_ack(sk, skb);
goto discard;
}
return true;
discard:
tcp_drop(sk, skb);
return false;
}
/*
* TCP receive function for the ESTABLISHED state.
*
* It is split into a fast path and a slow path. The fast path is
* disabled when:
* - A zero window was announced from us - zero window probing
* is only handled properly in the slow path.
* - Out of order segments arrived.
* - Urgent data is expected.
* - There is no buffer space left
* - Unexpected TCP flags/window values/header lengths are received
* (detected by checking the TCP header against pred_flags)
* - Data is sent in both directions. Fast path only supports pure senders
* or pure receivers (this means either the sequence number or the ack
* value must stay constant)
* - Unexpected TCP option.
*
* When these conditions are not satisfied it drops into a standard
* receive procedure patterned after RFC793 to handle all cases.
* The first three cases are guaranteed by proper pred_flags setting,
* the rest is checked inline. Fast processing is turned on in
* tcp_data_queue when everything is OK.
*/
void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
{
const struct tcphdr *th = (const struct tcphdr *)skb->data;
struct tcp_sock *tp = tcp_sk(sk);
unsigned int len = skb->len;
/* TCP congestion window tracking */
trace_tcp_probe(sk, skb);
tcp_mstamp_refresh(tp);
if (unlikely(!sk->sk_rx_dst))
inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
/*
* Header prediction.
* The code loosely follows the one in the famous
* "30 instruction TCP receive" Van Jacobson mail.
*
* Van's trick is to deposit buffers into socket queue
* on a device interrupt, to call tcp_recv function
* on the receive process context and checksum and copy
* the buffer to user space. smart...
*
* Our current scheme is not silly either but we take the
* extra cost of the net_bh soft interrupt processing...
* We do checksum and copy also but from device to kernel.
*/
tp->rx_opt.saw_tstamp = 0;
/* pred_flags is 0xS?10 << 16 + snd_wnd
* if header_prediction is to be made
* 'S' will always be tp->tcp_header_len >> 2
* '?' will be 0 for the fast path, otherwise pred_flags is 0 to
* turn it off (when there are holes in the receive
* space for instance)
* PSH flag is ignored.
*/
if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
int tcp_header_len = tp->tcp_header_len;
/* Timestamp header prediction: tcp_header_len
* is automatically equal to th->doff*4 due to pred_flags
* match.
*/
/* Check timestamp */
if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
/* No? Slow path! */
if (!tcp_parse_aligned_timestamp(tp, th))
goto slow_path;
/* If PAWS failed, check it more carefully in slow path */
if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
goto slow_path;
/* DO NOT update ts_recent here, if checksum fails
* and timestamp was corrupted part, it will result
* in a hung connection since we will drop all
* future packets due to the PAWS test.
*/
}
if (len <= tcp_header_len) {
/* Bulk data transfer: sender */
if (len == tcp_header_len) {
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
/* We know that such packets are checksummed
* on entry.
*/
tcp_ack(sk, skb, 0);
__kfree_skb(skb);
tcp_data_snd_check(sk);
/* When receiving pure ack in fast path, update
* last ts ecr directly instead of calling
* tcp_rcv_rtt_measure_ts()
*/
tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
return;
} else { /* Header too small */
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
goto discard;
}
} else {
int eaten = 0;
bool fragstolen = false;
if (tcp_checksum_complete(skb))
goto csum_error;
if ((int)skb->truesize > sk->sk_forward_alloc)
goto step5;
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
tcp_rcv_rtt_measure_ts(sk, skb);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
/* Bulk data transfer: receiver */
__skb_pull(skb, tcp_header_len);
eaten = tcp_queue_rcv(sk, skb, &fragstolen);
tcp_event_data_recv(sk, skb);
if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
/* Well, only one small jumplet in fast path... */
tcp_ack(sk, skb, FLAG_DATA);
tcp_data_snd_check(sk);
if (!inet_csk_ack_scheduled(sk))
goto no_ack;
}
__tcp_ack_snd_check(sk, 0);
no_ack:
if (eaten)
kfree_skb_partial(skb, fragstolen);
tcp_data_ready(sk);
return;
}
}
slow_path:
if (len < (th->doff << 2) || tcp_checksum_complete(skb))
goto csum_error;
if (!th->ack && !th->rst && !th->syn)
goto discard;
/*
* Standard slow path.
*/
if (!tcp_validate_incoming(sk, skb, th, 1))
return;
step5:
if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
goto discard;
tcp_rcv_rtt_measure_ts(sk, skb);
/* Process urgent data. */
tcp_urg(sk, skb, th);
/* step 7: process the segment text */
tcp_data_queue(sk, skb);
tcp_data_snd_check(sk);
tcp_ack_snd_check(sk);
return;
csum_error:
TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
discard:
tcp_drop(sk, skb);
}
EXPORT_SYMBOL(tcp_rcv_established);
void tcp_init_transfer(struct sock *sk, int bpf_op)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
tcp_mtup_init(sk);
icsk->icsk_af_ops->rebuild_header(sk);
tcp_init_metrics(sk);
/* Initialize the congestion window to start the transfer.
* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
* retransmitted. In light of RFC6298 more aggressive 1sec
* initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
* retransmission has occurred.
*/
if (tp->total_retrans > 1 && tp->undo_marker)
tp->snd_cwnd = 1;
else
tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
tp->snd_cwnd_stamp = tcp_jiffies32;
tcp_call_bpf(sk, bpf_op, 0, NULL);
tcp_init_congestion_control(sk);
tcp_init_buffer_space(sk);
}
void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_set_state(sk, TCP_ESTABLISHED);
icsk->icsk_ack.lrcvtime = tcp_jiffies32;
if (skb) {
icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
security_inet_conn_established(sk, skb);
sk_mark_napi_id(sk, skb);
}
tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB);
/* Prevent spurious tcp_cwnd_restart() on first data
* packet.
*/
tp->lsndtime = tcp_jiffies32;
if (sock_flag(sk, SOCK_KEEPOPEN))
inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
if (!tp->rx_opt.snd_wscale)
__tcp_fast_path_on(tp, tp->snd_wnd);
else
tp->pred_flags = 0;
}
static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
struct tcp_fastopen_cookie *cookie)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
bool syn_drop = false;
if (mss == tp->rx_opt.user_mss) {
struct tcp_options_received opt;
/* Get original SYNACK MSS value if user MSS sets mss_clamp */
tcp_clear_options(&opt);
opt.user_mss = opt.mss_clamp = 0;
tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
mss = opt.mss_clamp;
}
if (!tp->syn_fastopen) {
/* Ignore an unsolicited cookie */
cookie->len = -1;
} else if (tp->total_retrans) {
/* SYN timed out and the SYN-ACK neither has a cookie nor
* acknowledges data. Presumably the remote received only
* the retransmitted (regular) SYNs: either the original
* SYN-data or the corresponding SYN-ACK was dropped.
*/
syn_drop = (cookie->len < 0 && data);
} else if (cookie->len < 0 && !tp->syn_data) {
/* We requested a cookie but didn't get it. If we did not use
* the (old) exp opt format then try so next time (try_exp=1).
* Otherwise we go back to use the RFC7413 opt (try_exp=2).
*/
try_exp = tp->syn_fastopen_exp ? 2 : 1;
}
tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
if (data) { /* Retransmit unacked data in SYN */
skb_rbtree_walk_from(data) {
if (__tcp_retransmit_skb(sk, data, 1))
break;
}
tcp_rearm_rto(sk);
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPFASTOPENACTIVEFAIL);
return true;
}
tp->syn_data_acked = tp->syn_data;
if (tp->syn_data_acked) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
/* SYN-data is counted as two separate packets in tcp_ack() */
if (tp->delivered > 1)
--tp->delivered;
}
tcp_fastopen_add_skb(sk, synack);
return false;
}
static void smc_check_reset_syn(struct tcp_sock *tp)
{
#if IS_ENABLED(CONFIG_SMC)
if (static_branch_unlikely(&tcp_have_smc)) {
if (tp->syn_smc && !tp->rx_opt.smc_ok)
tp->syn_smc = 0;
}
#endif
}
static void tcp_try_undo_spurious_syn(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 syn_stamp;
/* undo_marker is set when SYN or SYNACK times out. The timeout is
* spurious if the ACK's timestamp option echo value matches the
* original SYN timestamp.
*/
syn_stamp = tp->retrans_stamp;
if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
syn_stamp == tp->rx_opt.rcv_tsecr)
tp->undo_marker = 0;
}
static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
const struct tcphdr *th)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_fastopen_cookie foc = { .len = -1 };
int saved_clamp = tp->rx_opt.mss_clamp;
bool fastopen_fail;
tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
tp->rx_opt.rcv_tsecr -= tp->tsoffset;
if (th->ack) {
/* rfc793:
* "If the state is SYN-SENT then
* first check the ACK bit
* If the ACK bit is set
* If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
* a reset (unless the RST bit is set, if so drop
* the segment and return)"
*/
if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
goto reset_and_undo;
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
!between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
tcp_time_stamp(tp))) {
NET_INC_STATS(sock_net(sk),
LINUX_MIB_PAWSACTIVEREJECTED);
goto reset_and_undo;
}
/* Now ACK is acceptable.
*
* "If the RST bit is set
* If the ACK was acceptable then signal the user "error:
* connection reset", drop the segment, enter CLOSED state,
* delete TCB, and return."
*/
if (th->rst) {
tcp_reset(sk);
goto discard;
}
/* rfc793:
* "fifth, if neither of the SYN or RST bits is set then
* drop the segment and return."
*
* See note below!
* --ANK(990513)
*/
if (!th->syn)
goto discard_and_undo;
/* rfc793:
* "If the SYN bit is on ...
* are acceptable then ...
* (our SYN has been ACKed), change the connection
* state to ESTABLISHED..."
*/
tcp_ecn_rcv_synack(tp, th);
tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
tcp_try_undo_spurious_syn(sk);
tcp_ack(sk, skb, FLAG_SLOWPATH);
/* Ok.. it's good. Set up sequence numbers and
* move to established.
*/
tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
*/
tp->snd_wnd = ntohs(th->window);
if (!tp->rx_opt.wscale_ok) {
tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
tp->window_clamp = min(tp->window_clamp, 65535U);
}
if (tp->rx_opt.saw_tstamp) {
tp->rx_opt.tstamp_ok = 1;
tp->tcp_header_len =
sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
tcp_store_ts_recent(tp);
} else {
tp->tcp_header_len = sizeof(struct tcphdr);
}
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
tcp_initialize_rcv_mss(sk);
/* Remember, tcp_poll() does not lock socket!
* Change state from SYN-SENT only after copied_seq
* is initialized. */
tp->copied_seq = tp->rcv_nxt;
smc_check_reset_syn(tp);
smp_mb();
tcp_finish_connect(sk, skb);
fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
tcp_rcv_fastopen_synack(sk, skb, &foc);
if (!sock_flag(sk, SOCK_DEAD)) {
sk->sk_state_change(sk);
sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
}
if (fastopen_fail)
return -1;
if (sk->sk_write_pending ||
icsk->icsk_accept_queue.rskq_defer_accept ||
inet_csk_in_pingpong_mode(sk)) {
/* Save one ACK. Data will be ready after
* several ticks, if write_pending is set.
*
* It may be deleted, but with this feature tcpdumps
* look so _wonderfully_ clever, that I was not able
* to stand against the temptation 8) --ANK
*/
inet_csk_schedule_ack(sk);
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
TCP_DELACK_MAX, TCP_RTO_MAX);
discard:
tcp_drop(sk, skb);
return 0;
} else {
tcp_send_ack(sk);
}
return -1;
}
/* No ACK in the segment */
if (th->rst) {
/* rfc793:
* "If the RST bit is set
*
* Otherwise (no ACK) drop the segment and return."
*/
goto discard_and_undo;
}
/* PAWS check. */
if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
tcp_paws_reject(&tp->rx_opt, 0))
goto discard_and_undo;
if (th->syn) {
/* We see SYN without ACK. It is attempt of
* simultaneous connect with crossed SYNs.
* Particularly, it can be connect to self.
*/
tcp_set_state(sk, TCP_SYN_RECV);
if (tp->rx_opt.saw_tstamp) {
tp->rx_opt.tstamp_ok = 1;
tcp_store_ts_recent(tp);
tp->tcp_header_len =
sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
} else {
tp->tcp_header_len = sizeof(struct tcphdr);
}
tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tp->copied_seq = tp->rcv_nxt;
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
*/
tp->snd_wnd = ntohs(th->window);
tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
tp->max_window = tp->snd_wnd;
tcp_ecn_rcv_syn(tp, th);
tcp_mtup_init(sk);
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
tcp_initialize_rcv_mss(sk);
tcp_send_synack(sk);
#if 0
/* Note, we could accept data and URG from this segment.
* There are no obstacles to make this (except that we must
* either change tcp_recvmsg() to prevent it from returning data
* before 3WHS completes per RFC793, or employ TCP Fast Open).
*
* However, if we ignore data in ACKless segments sometimes,
* we have no reasons to accept it sometimes.
* Also, seems the code doing it in step6 of tcp_rcv_state_process
* is not flawless. So, discard packet for sanity.
* Uncomment this return to process the data.
*/
return -1;
#else
goto discard;
#endif
}
/* "fifth, if neither of the SYN or RST bits is set then
* drop the segment and return."
*/
discard_and_undo:
tcp_clear_options(&tp->rx_opt);
tp->rx_opt.mss_clamp = saved_clamp;
goto discard;
reset_and_undo:
tcp_clear_options(&tp->rx_opt);
tp->rx_opt.mss_clamp = saved_clamp;
return 1;
}
static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
{
tcp_try_undo_loss(sk, false);
/* Reset rtx states to prevent spurious retransmits_timed_out() */
tcp_sk(sk)->retrans_stamp = 0;
inet_csk(sk)->icsk_retransmits = 0;
/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
* we no longer need req so release it.
*/
reqsk_fastopen_remove(sk, tcp_sk(sk)->fastopen_rsk, false);
/* Re-arm the timer because data may have been sent out.
* This is similar to the regular data transmission case
* when new data has just been ack'ed.
*
* (TFO) - we could try to be more aggressive and
* retransmitting any data sooner based on when they
* are sent out.
*/
tcp_rearm_rto(sk);
}
/*
* This function implements the receiving procedure of RFC 793 for
* all states except ESTABLISHED and TIME_WAIT.
* It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
* address independent.
*/
int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcphdr *th = tcp_hdr(skb);
struct request_sock *req;
int queued = 0;
bool acceptable;
switch (sk->sk_state) {
case TCP_CLOSE:
goto discard;
case TCP_LISTEN:
if (th->ack)
return 1;
if (th->rst)
goto discard;
if (th->syn) {
if (th->fin)
goto discard;
/* It is possible that we process SYN packets from backlog,
* so we need to make sure to disable BH and RCU right there.
*/
rcu_read_lock();
local_bh_disable();
acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
local_bh_enable();
rcu_read_unlock();
if (!acceptable)
return 1;
consume_skb(skb);
return 0;
}
goto discard;
case TCP_SYN_SENT:
tp->rx_opt.saw_tstamp = 0;
tcp_mstamp_refresh(tp);
queued = tcp_rcv_synsent_state_process(sk, skb, th);
if (queued >= 0)
return queued;
/* Do step6 onward by hand. */
tcp_urg(sk, skb, th);
__kfree_skb(skb);
tcp_data_snd_check(sk);
return 0;
}
tcp_mstamp_refresh(tp);
tp->rx_opt.saw_tstamp = 0;
req = tp->fastopen_rsk;
if (req) {
bool req_stolen;
WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
sk->sk_state != TCP_FIN_WAIT1);
if (!tcp_check_req(sk, skb, req, true, &req_stolen))
goto discard;
}
if (!th->ack && !th->rst && !th->syn)
goto discard;
if (!tcp_validate_incoming(sk, skb, th, 0))
return 0;
/* step 5: check the ACK field */
acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
FLAG_UPDATE_TS_RECENT |
FLAG_NO_CHALLENGE_ACK) > 0;
if (!acceptable) {
if (sk->sk_state == TCP_SYN_RECV)
return 1; /* send one RST */
tcp_send_challenge_ack(sk, skb);
goto discard;
}
switch (sk->sk_state) {
case TCP_SYN_RECV:
tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
if (!tp->srtt_us)
tcp_synack_rtt_meas(sk, req);
if (req) {
tcp_rcv_synrecv_state_fastopen(sk);
} else {
tcp_try_undo_spurious_syn(sk);
tp->retrans_stamp = 0;
tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
tp->copied_seq = tp->rcv_nxt;
}
smp_mb();
tcp_set_state(sk, TCP_ESTABLISHED);
sk->sk_state_change(sk);
/* Note, that this wakeup is only for marginal crossed SYN case.
* Passively open sockets are not waked up, because
* sk->sk_sleep == NULL and sk->sk_socket == NULL.
*/
if (sk->sk_socket)
sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
if (!inet_csk(sk)->icsk_ca_ops->cong_control)
tcp_update_pacing_rate(sk);
/* Prevent spurious tcp_cwnd_restart() on first data packet */
tp->lsndtime = tcp_jiffies32;
tcp_initialize_rcv_mss(sk);
tcp_fast_path_on(tp);
break;
case TCP_FIN_WAIT1: {
int tmo;
if (req)
tcp_rcv_synrecv_state_fastopen(sk);
if (tp->snd_una != tp->write_seq)
break;
tcp_set_state(sk, TCP_FIN_WAIT2);
sk->sk_shutdown |= SEND_SHUTDOWN;
sk_dst_confirm(sk);
if (!sock_flag(sk, SOCK_DEAD)) {
/* Wake up lingering close() */
sk->sk_state_change(sk);
break;
}
if (tp->linger2 < 0) {
tcp_done(sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
return 1;
}
if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
/* Receive out of order FIN after close() */
if (tp->syn_fastopen && th->fin)
tcp_fastopen_active_disable(sk);
tcp_done(sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
return 1;
}
tmo = tcp_fin_time(sk);
if (tmo > TCP_TIMEWAIT_LEN) {
inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
} else if (th->fin || sock_owned_by_user(sk)) {
/* Bad case. We could lose such FIN otherwise.
* It is not a big problem, but it looks confusing
* and not so rare event. We still can lose it now,
* if it spins in bh_lock_sock(), but it is really
* marginal case.
*/
inet_csk_reset_keepalive_timer(sk, tmo);
} else {
tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
goto discard;
}
break;
}
case TCP_CLOSING:
if (tp->snd_una == tp->write_seq) {
tcp_time_wait(sk, TCP_TIME_WAIT, 0);
goto discard;
}
break;
case TCP_LAST_ACK:
if (tp->snd_una == tp->write_seq) {
tcp_update_metrics(sk);
tcp_done(sk);
goto discard;
}
break;
}
/* step 6: check the URG bit */
tcp_urg(sk, skb, th);
/* step 7: process the segment text */
switch (sk->sk_state) {
case TCP_CLOSE_WAIT:
case TCP_CLOSING:
case TCP_LAST_ACK:
if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
break;
/* fall through */
case TCP_FIN_WAIT1:
case TCP_FIN_WAIT2:
/* RFC 793 says to queue data in these states,
* RFC 1122 says we MUST send a reset.
* BSD 4.4 also does reset.
*/
if (sk->sk_shutdown & RCV_SHUTDOWN) {
if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
tcp_reset(sk);
return 1;
}
}
/* Fall through */
case TCP_ESTABLISHED:
tcp_data_queue(sk, skb);
queued = 1;
break;
}
/* tcp_data could move socket to TIME-WAIT */
if (sk->sk_state != TCP_CLOSE) {
tcp_data_snd_check(sk);
tcp_ack_snd_check(sk);
}
if (!queued) {
discard:
tcp_drop(sk, skb);
}
return 0;
}
EXPORT_SYMBOL(tcp_rcv_state_process);
static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
{
struct inet_request_sock *ireq = inet_rsk(req);
if (family == AF_INET)
net_dbg_ratelimited("drop open request from %pI4/%u\n",
&ireq->ir_rmt_addr, port);
#if IS_ENABLED(CONFIG_IPV6)
else if (family == AF_INET6)
net_dbg_ratelimited("drop open request from %pI6/%u\n",
&ireq->ir_v6_rmt_addr, port);
#endif
}
/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
*
* If we receive a SYN packet with these bits set, it means a
* network is playing bad games with TOS bits. In order to
* avoid possible false congestion notifications, we disable
* TCP ECN negotiation.
*
* Exception: tcp_ca wants ECN. This is required for DCTCP
* congestion control: Linux DCTCP asserts ECT on all packets,
* including SYN, which is most optimal solution; however,
* others, such as FreeBSD do not.
*
* Exception: At least one of the reserved bits of the TCP header (th->res1) is
* set, indicating the use of a future TCP extension (such as AccECN). See
* RFC8311 §4.3 which updates RFC3168 to allow the development of such
* extensions.
*/
static void tcp_ecn_create_request(struct request_sock *req,
const struct sk_buff *skb,
const struct sock *listen_sk,
const struct dst_entry *dst)
{
const struct tcphdr *th = tcp_hdr(skb);
const struct net *net = sock_net(listen_sk);
bool th_ecn = th->ece && th->cwr;
bool ect, ecn_ok;
u32 ecn_ok_dst;
if (!th_ecn)
return;
ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
(ecn_ok_dst & DST_FEATURE_ECN_CA) ||
tcp_bpf_ca_needs_ecn((struct sock *)req))
inet_rsk(req)->ecn_ok = 1;
}
static void tcp_openreq_init(struct request_sock *req,
const struct tcp_options_received *rx_opt,
struct sk_buff *skb, const struct sock *sk)
{
struct inet_request_sock *ireq = inet_rsk(req);
req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */
req->cookie_ts = 0;
tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tcp_rsk(req)->snt_synack = 0;
tcp_rsk(req)->last_oow_ack_time = 0;
req->mss = rx_opt->mss_clamp;
req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
ireq->tstamp_ok = rx_opt->tstamp_ok;
ireq->sack_ok = rx_opt->sack_ok;
ireq->snd_wscale = rx_opt->snd_wscale;
ireq->wscale_ok = rx_opt->wscale_ok;
ireq->acked = 0;
ireq->ecn_ok = 0;
ireq->ir_rmt_port = tcp_hdr(skb)->source;
ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
ireq->ir_mark = inet_request_mark(sk, skb);
#if IS_ENABLED(CONFIG_SMC)
ireq->smc_ok = rx_opt->smc_ok;
#endif
}
struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
struct sock *sk_listener,
bool attach_listener)
{
struct request_sock *req = reqsk_alloc(ops, sk_listener,
attach_listener);
if (req) {
struct inet_request_sock *ireq = inet_rsk(req);
ireq->ireq_opt = NULL;
#if IS_ENABLED(CONFIG_IPV6)
ireq->pktopts = NULL;
#endif
atomic64_set(&ireq->ir_cookie, 0);
ireq->ireq_state = TCP_NEW_SYN_RECV;
write_pnet(&ireq->ireq_net, sock_net(sk_listener));
ireq->ireq_family = sk_listener->sk_family;
}
return req;
}
EXPORT_SYMBOL(inet_reqsk_alloc);
/*
* Return true if a syncookie should be sent
*/
static bool tcp_syn_flood_action(const struct sock *sk,
const struct sk_buff *skb,
const char *proto)
{
struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
const char *msg = "Dropping request";
bool want_cookie = false;
struct net *net = sock_net(sk);
#ifdef CONFIG_SYN_COOKIES
if (net->ipv4.sysctl_tcp_syncookies) {
msg = "Sending cookies";
want_cookie = true;
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
} else
#endif
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
if (!queue->synflood_warned &&
net->ipv4.sysctl_tcp_syncookies != 2 &&
xchg(&queue->synflood_warned, 1) == 0)
net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
proto, ntohs(tcp_hdr(skb)->dest), msg);
return want_cookie;
}
static void tcp_reqsk_record_syn(const struct sock *sk,
struct request_sock *req,
const struct sk_buff *skb)
{
if (tcp_sk(sk)->save_syn) {
u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
u32 *copy;
copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
if (copy) {
copy[0] = len;
memcpy(&copy[1], skb_network_header(skb), len);
req->saved_syn = copy;
}
}
}
int tcp_conn_request(struct request_sock_ops *rsk_ops,
const struct tcp_request_sock_ops *af_ops,
struct sock *sk, struct sk_buff *skb)
{
struct tcp_fastopen_cookie foc = { .len = -1 };
__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
struct tcp_options_received tmp_opt;
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
struct sock *fastopen_sk = NULL;
struct request_sock *req;
bool want_cookie = false;
struct dst_entry *dst;
struct flowi fl;
/* TW buckets are converted to open requests without
* limitations, they conserve resources and peer is
* evidently real one.
*/
if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
inet_csk_reqsk_queue_is_full(sk)) && !isn) {
want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
if (!want_cookie)
goto drop;
}
if (sk_acceptq_is_full(sk)) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
goto drop;
}
req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
if (!req)
goto drop;
tcp_rsk(req)->af_specific = af_ops;
tcp_rsk(req)->ts_off = 0;
tcp_clear_options(&tmp_opt);
tmp_opt.mss_clamp = af_ops->mss_clamp;
tmp_opt.user_mss = tp->rx_opt.user_mss;
tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
want_cookie ? NULL : &foc);
if (want_cookie && !tmp_opt.saw_tstamp)
tcp_clear_options(&tmp_opt);
if (IS_ENABLED(CONFIG_SMC) && want_cookie)
tmp_opt.smc_ok = 0;
tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
tcp_openreq_init(req, &tmp_opt, skb, sk);
inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
/* Note: tcp_v6_init_req() might override ir_iif for link locals */
inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
af_ops->init_req(req, sk, skb);
if (security_inet_conn_request(sk, skb, req))
goto drop_and_free;
if (tmp_opt.tstamp_ok)
tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
dst = af_ops->route_req(sk, &fl, req);
if (!dst)
goto drop_and_free;
if (!want_cookie && !isn) {
/* Kill the following clause, if you dislike this way. */
if (!net->ipv4.sysctl_tcp_syncookies &&
(net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
(net->ipv4.sysctl_max_syn_backlog >> 2)) &&
!tcp_peer_is_proven(req, dst)) {
/* Without syncookies last quarter of
* backlog is filled with destinations,
* proven to be alive.
* It means that we continue to communicate
* to destinations, already remembered
* to the moment of synflood.
*/
pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
rsk_ops->family);
goto drop_and_release;
}
isn = af_ops->init_seq(skb);
}
tcp_ecn_create_request(req, skb, sk, dst);
if (want_cookie) {
isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
req->cookie_ts = tmp_opt.tstamp_ok;
if (!tmp_opt.tstamp_ok)
inet_rsk(req)->ecn_ok = 0;
}
tcp_rsk(req)->snt_isn = isn;
tcp_rsk(req)->txhash = net_tx_rndhash();
tcp_openreq_init_rwin(req, sk, dst);
sk_rx_queue_set(req_to_sk(req), skb);
if (!want_cookie) {
tcp_reqsk_record_syn(sk, req, skb);
fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
}
if (fastopen_sk) {
af_ops->send_synack(fastopen_sk, dst, &fl, req,
&foc, TCP_SYNACK_FASTOPEN);
/* Add the child socket directly into the accept queue */
if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
reqsk_fastopen_remove(fastopen_sk, req, false);
bh_unlock_sock(fastopen_sk);
sock_put(fastopen_sk);
goto drop_and_free;
}
sk->sk_data_ready(sk);
bh_unlock_sock(fastopen_sk);
sock_put(fastopen_sk);
} else {
tcp_rsk(req)->tfo_listener = false;
if (!want_cookie)
inet_csk_reqsk_queue_hash_add(sk, req,
tcp_timeout_init((struct sock *)req));
af_ops->send_synack(sk, dst, &fl, req, &foc,
!want_cookie ? TCP_SYNACK_NORMAL :
TCP_SYNACK_COOKIE);
if (want_cookie) {
reqsk_free(req);
return 0;
}
}
reqsk_put(req);
return 0;
drop_and_release:
dst_release(dst);
drop_and_free:
__reqsk_free(req);
drop:
tcp_listendrop(sk);
return 0;
}
EXPORT_SYMBOL(tcp_conn_request);
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