flow_dissector: implements eBPF parser
This eBPF program extracts basic/control/ip address/ports keys from incoming packets. It supports recursive parsing for IP encapsulation, and VLAN, along with IPv4/IPv6 and extension headers. This program is meant to show how flow dissection and key extraction can be done in eBPF. Link: http://vger.kernel.org/netconf2017_files/rx_hardening_and_udp_gso.pdf Signed-off-by: Petar Penkov <ppenkov@google.com> Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Petar Penkov
Alexei Starovoitov
Родитель
c22fbae76c
Коммит
9c98b13cc3
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@ -35,7 +35,7 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
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test_get_stack_rawtp.o test_sockmap_kern.o test_sockhash_kern.o \
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test_lwt_seg6local.o sendmsg4_prog.o sendmsg6_prog.o test_lirc_mode2_kern.o \
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get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \
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test_skb_cgroup_id_kern.o
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test_skb_cgroup_id_kern.o bpf_flow.o
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# Order correspond to 'make run_tests' order
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TEST_PROGS := test_kmod.sh \
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@ -0,0 +1,373 @@
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// SPDX-License-Identifier: GPL-2.0
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#include <limits.h>
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#include <stddef.h>
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#include <stdbool.h>
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#include <string.h>
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#include <linux/pkt_cls.h>
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#include <linux/bpf.h>
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#include <linux/in.h>
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#include <linux/if_ether.h>
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#include <linux/icmp.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include <linux/tcp.h>
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#include <linux/udp.h>
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#include <linux/if_packet.h>
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#include <sys/socket.h>
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#include <linux/if_tunnel.h>
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#include <linux/mpls.h>
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#include "bpf_helpers.h"
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#include "bpf_endian.h"
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int _version SEC("version") = 1;
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#define PROG(F) SEC(#F) int bpf_func_##F
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/* These are the identifiers of the BPF programs that will be used in tail
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* calls. Name is limited to 16 characters, with the terminating character and
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* bpf_func_ above, we have only 6 to work with, anything after will be cropped.
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*/
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enum {
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IP,
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IPV6,
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IPV6OP, /* Destination/Hop-by-Hop Options IPv6 Extension header */
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IPV6FR, /* Fragmentation IPv6 Extension Header */
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MPLS,
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VLAN,
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};
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#define IP_MF 0x2000
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#define IP_OFFSET 0x1FFF
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#define IP6_MF 0x0001
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#define IP6_OFFSET 0xFFF8
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struct vlan_hdr {
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__be16 h_vlan_TCI;
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__be16 h_vlan_encapsulated_proto;
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};
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struct gre_hdr {
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__be16 flags;
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__be16 proto;
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};
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struct frag_hdr {
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__u8 nexthdr;
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__u8 reserved;
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__be16 frag_off;
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__be32 identification;
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};
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struct bpf_map_def SEC("maps") jmp_table = {
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.type = BPF_MAP_TYPE_PROG_ARRAY,
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.key_size = sizeof(__u32),
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.value_size = sizeof(__u32),
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.max_entries = 8
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};
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static __always_inline void *bpf_flow_dissect_get_header(struct __sk_buff *skb,
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__u16 hdr_size,
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void *buffer)
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{
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void *data_end = (void *)(long)skb->data_end;
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void *data = (void *)(long)skb->data;
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__u16 nhoff = skb->flow_keys->nhoff;
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__u8 *hdr;
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/* Verifies this variable offset does not overflow */
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if (nhoff > (USHRT_MAX - hdr_size))
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return NULL;
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hdr = data + nhoff;
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if (hdr + hdr_size <= data_end)
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return hdr;
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if (bpf_skb_load_bytes(skb, nhoff, buffer, hdr_size))
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return NULL;
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return buffer;
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}
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/* Dispatches on ETHERTYPE */
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static __always_inline int parse_eth_proto(struct __sk_buff *skb, __be16 proto)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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keys->n_proto = proto;
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switch (proto) {
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case bpf_htons(ETH_P_IP):
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bpf_tail_call(skb, &jmp_table, IP);
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break;
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case bpf_htons(ETH_P_IPV6):
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bpf_tail_call(skb, &jmp_table, IPV6);
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break;
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case bpf_htons(ETH_P_MPLS_MC):
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case bpf_htons(ETH_P_MPLS_UC):
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bpf_tail_call(skb, &jmp_table, MPLS);
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break;
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case bpf_htons(ETH_P_8021Q):
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case bpf_htons(ETH_P_8021AD):
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bpf_tail_call(skb, &jmp_table, VLAN);
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break;
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default:
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/* Protocol not supported */
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return BPF_DROP;
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}
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return BPF_DROP;
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}
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SEC("dissect")
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int dissect(struct __sk_buff *skb)
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{
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if (!skb->vlan_present)
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return parse_eth_proto(skb, skb->protocol);
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else
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return parse_eth_proto(skb, skb->vlan_proto);
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}
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/* Parses on IPPROTO_* */
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static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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void *data_end = (void *)(long)skb->data_end;
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struct icmphdr *icmp, _icmp;
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struct gre_hdr *gre, _gre;
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struct ethhdr *eth, _eth;
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struct tcphdr *tcp, _tcp;
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struct udphdr *udp, _udp;
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keys->ip_proto = proto;
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switch (proto) {
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case IPPROTO_ICMP:
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icmp = bpf_flow_dissect_get_header(skb, sizeof(*icmp), &_icmp);
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if (!icmp)
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return BPF_DROP;
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return BPF_OK;
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case IPPROTO_IPIP:
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keys->is_encap = true;
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return parse_eth_proto(skb, bpf_htons(ETH_P_IP));
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case IPPROTO_IPV6:
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keys->is_encap = true;
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return parse_eth_proto(skb, bpf_htons(ETH_P_IPV6));
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case IPPROTO_GRE:
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gre = bpf_flow_dissect_get_header(skb, sizeof(*gre), &_gre);
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if (!gre)
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return BPF_DROP;
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if (bpf_htons(gre->flags & GRE_VERSION))
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/* Only inspect standard GRE packets with version 0 */
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return BPF_OK;
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keys->nhoff += sizeof(*gre); /* Step over GRE Flags and Proto */
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if (GRE_IS_CSUM(gre->flags))
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keys->nhoff += 4; /* Step over chksum and Padding */
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if (GRE_IS_KEY(gre->flags))
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keys->nhoff += 4; /* Step over key */
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if (GRE_IS_SEQ(gre->flags))
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keys->nhoff += 4; /* Step over sequence number */
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keys->is_encap = true;
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if (gre->proto == bpf_htons(ETH_P_TEB)) {
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eth = bpf_flow_dissect_get_header(skb, sizeof(*eth),
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&_eth);
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if (!eth)
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return BPF_DROP;
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keys->nhoff += sizeof(*eth);
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return parse_eth_proto(skb, eth->h_proto);
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} else {
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return parse_eth_proto(skb, gre->proto);
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}
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case IPPROTO_TCP:
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tcp = bpf_flow_dissect_get_header(skb, sizeof(*tcp), &_tcp);
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if (!tcp)
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return BPF_DROP;
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if (tcp->doff < 5)
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return BPF_DROP;
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if ((__u8 *)tcp + (tcp->doff << 2) > data_end)
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return BPF_DROP;
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keys->thoff = keys->nhoff;
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keys->sport = tcp->source;
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keys->dport = tcp->dest;
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return BPF_OK;
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case IPPROTO_UDP:
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case IPPROTO_UDPLITE:
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udp = bpf_flow_dissect_get_header(skb, sizeof(*udp), &_udp);
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if (!udp)
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return BPF_DROP;
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keys->thoff = keys->nhoff;
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keys->sport = udp->source;
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keys->dport = udp->dest;
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return BPF_OK;
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default:
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return BPF_DROP;
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}
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return BPF_DROP;
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}
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static __always_inline int parse_ipv6_proto(struct __sk_buff *skb, __u8 nexthdr)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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keys->ip_proto = nexthdr;
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switch (nexthdr) {
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case IPPROTO_HOPOPTS:
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case IPPROTO_DSTOPTS:
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bpf_tail_call(skb, &jmp_table, IPV6OP);
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break;
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case IPPROTO_FRAGMENT:
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bpf_tail_call(skb, &jmp_table, IPV6FR);
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break;
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default:
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return parse_ip_proto(skb, nexthdr);
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}
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return BPF_DROP;
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}
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PROG(IP)(struct __sk_buff *skb)
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{
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void *data_end = (void *)(long)skb->data_end;
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struct bpf_flow_keys *keys = skb->flow_keys;
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void *data = (void *)(long)skb->data;
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struct iphdr *iph, _iph;
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bool done = false;
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iph = bpf_flow_dissect_get_header(skb, sizeof(*iph), &_iph);
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if (!iph)
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return BPF_DROP;
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/* IP header cannot be smaller than 20 bytes */
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if (iph->ihl < 5)
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return BPF_DROP;
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keys->addr_proto = ETH_P_IP;
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keys->ipv4_src = iph->saddr;
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keys->ipv4_dst = iph->daddr;
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keys->nhoff += iph->ihl << 2;
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if (data + keys->nhoff > data_end)
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return BPF_DROP;
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if (iph->frag_off & bpf_htons(IP_MF | IP_OFFSET)) {
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keys->is_frag = true;
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if (iph->frag_off & bpf_htons(IP_OFFSET))
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/* From second fragment on, packets do not have headers
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* we can parse.
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*/
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done = true;
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else
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keys->is_first_frag = true;
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}
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if (done)
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return BPF_OK;
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return parse_ip_proto(skb, iph->protocol);
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}
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PROG(IPV6)(struct __sk_buff *skb)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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struct ipv6hdr *ip6h, _ip6h;
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ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
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if (!ip6h)
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return BPF_DROP;
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keys->addr_proto = ETH_P_IPV6;
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memcpy(&keys->ipv6_src, &ip6h->saddr, 2*sizeof(ip6h->saddr));
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keys->nhoff += sizeof(struct ipv6hdr);
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return parse_ipv6_proto(skb, ip6h->nexthdr);
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}
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PROG(IPV6OP)(struct __sk_buff *skb)
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{
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struct ipv6_opt_hdr *ip6h, _ip6h;
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ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
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if (!ip6h)
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return BPF_DROP;
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/* hlen is in 8-octets and does not include the first 8 bytes
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* of the header
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*/
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skb->flow_keys->nhoff += (1 + ip6h->hdrlen) << 3;
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return parse_ipv6_proto(skb, ip6h->nexthdr);
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}
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PROG(IPV6FR)(struct __sk_buff *skb)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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struct frag_hdr *fragh, _fragh;
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fragh = bpf_flow_dissect_get_header(skb, sizeof(*fragh), &_fragh);
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if (!fragh)
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return BPF_DROP;
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keys->nhoff += sizeof(*fragh);
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keys->is_frag = true;
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if (!(fragh->frag_off & bpf_htons(IP6_OFFSET)))
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keys->is_first_frag = true;
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return parse_ipv6_proto(skb, fragh->nexthdr);
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}
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PROG(MPLS)(struct __sk_buff *skb)
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{
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struct mpls_label *mpls, _mpls;
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mpls = bpf_flow_dissect_get_header(skb, sizeof(*mpls), &_mpls);
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if (!mpls)
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return BPF_DROP;
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return BPF_OK;
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}
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PROG(VLAN)(struct __sk_buff *skb)
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{
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struct bpf_flow_keys *keys = skb->flow_keys;
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struct vlan_hdr *vlan, _vlan;
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__be16 proto;
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/* Peek back to see if single or double-tagging */
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if (bpf_skb_load_bytes(skb, keys->nhoff - sizeof(proto), &proto,
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sizeof(proto)))
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return BPF_DROP;
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/* Account for double-tagging */
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if (proto == bpf_htons(ETH_P_8021AD)) {
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vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
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if (!vlan)
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return BPF_DROP;
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if (vlan->h_vlan_encapsulated_proto != bpf_htons(ETH_P_8021Q))
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return BPF_DROP;
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keys->nhoff += sizeof(*vlan);
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}
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vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
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if (!vlan)
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return BPF_DROP;
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keys->nhoff += sizeof(*vlan);
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/* Only allow 8021AD + 8021Q double tagging and no triple tagging.*/
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if (vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021AD) ||
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vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021Q))
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return BPF_DROP;
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return parse_eth_proto(skb, vlan->h_vlan_encapsulated_proto);
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}
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char __license[] SEC("license") = "GPL";
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