2020-07-30 22:25:56 +03:00
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// SPDX-License-Identifier: GPL-2.0
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#include <linux/skbuff.h>
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#include "protocol.h"
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/* Syncookies do not work for JOIN requests.
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*
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* Unlike MP_CAPABLE, where the ACK cookie contains the needed MPTCP
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* options to reconstruct the initial syn state, MP_JOIN does not contain
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* the token to obtain the mptcp socket nor the server-generated nonce
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* that was used in the cookie SYN/ACK response.
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*
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* Keep a small best effort state table to store the syn/synack data,
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* indexed by skb hash.
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*
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* A MP_JOIN SYN packet handled by syn cookies is only stored if the 32bit
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* token matches a known mptcp connection that can still accept more subflows.
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*
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* There is no timeout handling -- state is only re-constructed
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* when the TCP ACK passed the cookie validation check.
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*/
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struct join_entry {
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u32 token;
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u32 remote_nonce;
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u32 local_nonce;
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u8 join_id;
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u8 local_id;
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u8 backup;
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u8 valid;
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};
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#define COOKIE_JOIN_SLOTS 1024
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static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
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static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
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static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)
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{
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mptcp: fix warning in __skb_flow_dissect() when do syn cookie for subflow join
I did stress test with wrk[1] and webfsd[2] with the assistance of
mptcp-tools[3]:
Server side:
./use_mptcp.sh webfsd -4 -R /tmp/ -p 8099
Client side:
./use_mptcp.sh wrk -c 200 -d 30 -t 4 http://192.168.174.129:8099/
and got the following warning message:
[ 55.552626] TCP: request_sock_subflow: Possible SYN flooding on port 8099. Sending cookies. Check SNMP counters.
[ 55.553024] ------------[ cut here ]------------
[ 55.553027] WARNING: CPU: 0 PID: 10 at net/core/flow_dissector.c:984 __skb_flow_dissect+0x280/0x1650
...
[ 55.553117] CPU: 0 PID: 10 Comm: ksoftirqd/0 Not tainted 5.12.0+ #18
[ 55.553121] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[ 55.553124] RIP: 0010:__skb_flow_dissect+0x280/0x1650
...
[ 55.553133] RSP: 0018:ffffb79580087770 EFLAGS: 00010246
[ 55.553137] RAX: 0000000000000000 RBX: ffffffff8ddb58e0 RCX: ffffb79580087888
[ 55.553139] RDX: ffffffff8ddb58e0 RSI: ffff8f7e4652b600 RDI: 0000000000000000
[ 55.553141] RBP: ffffb79580087858 R08: 0000000000000000 R09: 0000000000000008
[ 55.553143] R10: 000000008c622965 R11: 00000000d3313a5b R12: ffff8f7e4652b600
[ 55.553146] R13: ffff8f7e465c9062 R14: 0000000000000000 R15: ffffb79580087888
[ 55.553149] FS: 0000000000000000(0000) GS:ffff8f7f75e00000(0000) knlGS:0000000000000000
[ 55.553152] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 55.553154] CR2: 00007f73d1d19000 CR3: 0000000135e10004 CR4: 00000000003706f0
[ 55.553160] Call Trace:
[ 55.553166] ? __sha256_final+0x67/0xd0
[ 55.553173] ? sha256+0x7e/0xa0
[ 55.553177] __skb_get_hash+0x57/0x210
[ 55.553182] subflow_init_req_cookie_join_save+0xac/0xc0
[ 55.553189] subflow_check_req+0x474/0x550
[ 55.553195] ? ip_route_output_key_hash+0x67/0x90
[ 55.553200] ? xfrm_lookup_route+0x1d/0xa0
[ 55.553207] subflow_v4_route_req+0x8e/0xd0
[ 55.553212] tcp_conn_request+0x31e/0xab0
[ 55.553218] ? selinux_socket_sock_rcv_skb+0x116/0x210
[ 55.553224] ? tcp_rcv_state_process+0x179/0x6d0
[ 55.553229] tcp_rcv_state_process+0x179/0x6d0
[ 55.553235] tcp_v4_do_rcv+0xaf/0x220
[ 55.553239] tcp_v4_rcv+0xce4/0xd80
[ 55.553243] ? ip_route_input_rcu+0x246/0x260
[ 55.553248] ip_protocol_deliver_rcu+0x35/0x1b0
[ 55.553253] ip_local_deliver_finish+0x44/0x50
[ 55.553258] ip_local_deliver+0x6c/0x110
[ 55.553262] ? ip_rcv_finish_core.isra.19+0x5a/0x400
[ 55.553267] ip_rcv+0xd1/0xe0
...
After debugging, I found in __skb_flow_dissect(), skb->dev and skb->sk
are both NULL, then net is NULL, and trigger WARN_ON_ONCE(!net),
actually net is always NULL in this code path, as skb->dev is set to
NULL in tcp_v4_rcv(), and skb->sk is never set.
Code snippet in __skb_flow_dissect() that trigger warning:
975 if (skb) {
976 if (!net) {
977 if (skb->dev)
978 net = dev_net(skb->dev);
979 else if (skb->sk)
980 net = sock_net(skb->sk);
981 }
982 }
983
984 WARN_ON_ONCE(!net);
So, using seq and transport header derived hash.
[1] https://github.com/wg/wrk
[2] https://github.com/ourway/webfsd
[3] https://github.com/pabeni/mptcp-tools
Fixes: 9466a1ccebbe ("mptcp: enable JOIN requests even if cookies are in use")
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jianguo Wu <wujianguo@chinatelecom.cn>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2021-07-10 03:20:46 +03:00
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static u32 mptcp_join_hash_secret __read_mostly;
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struct tcphdr *th = tcp_hdr(skb);
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u32 seq, i;
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net_get_random_once(&mptcp_join_hash_secret,
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sizeof(mptcp_join_hash_secret));
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if (th->syn)
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seq = TCP_SKB_CB(skb)->seq;
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else
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seq = TCP_SKB_CB(skb)->seq - 1;
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i = jhash_3words(seq, net_hash_mix(net),
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(__force __u32)th->source << 16 | (__force __u32)th->dest,
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mptcp_join_hash_secret);
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2020-07-30 22:25:56 +03:00
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return i % ARRAY_SIZE(join_entries);
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}
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static void mptcp_join_store_state(struct join_entry *entry,
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const struct mptcp_subflow_request_sock *subflow_req)
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{
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entry->token = subflow_req->token;
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entry->remote_nonce = subflow_req->remote_nonce;
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entry->local_nonce = subflow_req->local_nonce;
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entry->backup = subflow_req->backup;
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entry->join_id = subflow_req->remote_id;
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entry->local_id = subflow_req->local_id;
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entry->valid = 1;
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}
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void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
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struct sk_buff *skb)
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{
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struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
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u32 i = mptcp_join_entry_hash(skb, net);
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/* No use in waiting if other cpu is already using this slot --
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* would overwrite the data that got stored.
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*/
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spin_lock_bh(&join_entry_locks[i]);
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mptcp_join_store_state(&join_entries[i], subflow_req);
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spin_unlock_bh(&join_entry_locks[i]);
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}
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/* Called for a cookie-ack with MP_JOIN option present.
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* Look up the saved state based on skb hash & check token matches msk
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* in same netns.
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*
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* Caller will check msk can still accept another subflow. The hmac
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* present in the cookie ACK mptcp option space will be checked later.
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*/
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bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
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struct sk_buff *skb)
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{
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struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
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u32 i = mptcp_join_entry_hash(skb, net);
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struct mptcp_sock *msk;
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struct join_entry *e;
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e = &join_entries[i];
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spin_lock_bh(&join_entry_locks[i]);
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if (e->valid == 0) {
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spin_unlock_bh(&join_entry_locks[i]);
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return false;
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}
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e->valid = 0;
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msk = mptcp_token_get_sock(e->token);
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if (!msk) {
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spin_unlock_bh(&join_entry_locks[i]);
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return false;
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}
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/* If this fails, the token got re-used in the mean time by another
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* mptcp socket in a different netns, i.e. entry is outdated.
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*/
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if (!net_eq(sock_net((struct sock *)msk), net))
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goto err_put;
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subflow_req->remote_nonce = e->remote_nonce;
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subflow_req->local_nonce = e->local_nonce;
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subflow_req->backup = e->backup;
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subflow_req->remote_id = e->join_id;
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subflow_req->token = e->token;
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subflow_req->msk = msk;
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spin_unlock_bh(&join_entry_locks[i]);
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return true;
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err_put:
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spin_unlock_bh(&join_entry_locks[i]);
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sock_put((struct sock *)msk);
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return false;
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}
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void __init mptcp_join_cookie_init(void)
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{
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int i;
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2020-08-01 17:39:59 +03:00
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for (i = 0; i < COOKIE_JOIN_SLOTS; i++)
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2020-07-30 22:25:56 +03:00
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spin_lock_init(&join_entry_locks[i]);
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}
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