// SPDX-License-Identifier: GPL-2.0
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// Copyright (c) 2018 Facebook
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// Copyright (c) 2019 Cloudflare
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#include <string.h>
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#include <linux/bpf.h>
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#include <linux/pkt_cls.h>
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#include <linux/if_ether.h>
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#include <linux/in.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include <sys/socket.h>
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#include <linux/tcp.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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struct bpf_map_def SEC("maps") results = {
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.type = BPF_MAP_TYPE_ARRAY,
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.key_size = sizeof(__u32),
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.value_size = sizeof(__u32),
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.max_entries = 3,
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};
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static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
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void *iph, __u32 ip_size,
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struct tcphdr *tcph)
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{
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__u32 thlen = tcph->doff * 4;
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if (tcph->syn && !tcph->ack) {
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// packet should only have an MSS option
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if (thlen != 24)
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return 0;
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if ((void *)tcph + thlen > data_end)
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return 0;
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return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
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}
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return 0;
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}
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static __always_inline void check_syncookie(void *ctx, void *data,
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void *data_end)
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{
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struct bpf_sock_tuple tup;
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struct bpf_sock *sk;
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struct ethhdr *ethh;
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struct iphdr *ipv4h;
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struct ipv6hdr *ipv6h;
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struct tcphdr *tcph;
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int ret;
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__u32 key_mss = 2;
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__u32 key_gen = 1;
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__u32 key = 0;
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__s64 seq_mss;
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ethh = data;
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if (ethh + 1 > data_end)
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return;
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switch (bpf_ntohs(ethh->h_proto)) {
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case ETH_P_IP:
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ipv4h = data + sizeof(struct ethhdr);
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if (ipv4h + 1 > data_end)
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return;
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if (ipv4h->ihl != 5)
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return;
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tcph = data + sizeof(struct ethhdr) + sizeof(struct iphdr);
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if (tcph + 1 > data_end)
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return;
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tup.ipv4.saddr = ipv4h->saddr;
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tup.ipv4.daddr = ipv4h->daddr;
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tup.ipv4.sport = tcph->source;
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tup.ipv4.dport = tcph->dest;
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sk = bpf_skc_lookup_tcp(ctx, &tup, sizeof(tup.ipv4),
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BPF_F_CURRENT_NETNS, 0);
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if (!sk)
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return;
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if (sk->state != BPF_TCP_LISTEN)
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goto release;
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seq_mss = gen_syncookie(data_end, sk, ipv4h, sizeof(*ipv4h),
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tcph);
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ret = bpf_tcp_check_syncookie(sk, ipv4h, sizeof(*ipv4h),
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tcph, sizeof(*tcph));
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break;
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case ETH_P_IPV6:
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ipv6h = data + sizeof(struct ethhdr);
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if (ipv6h + 1 > data_end)
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return;
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if (ipv6h->nexthdr != IPPROTO_TCP)
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return;
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tcph = data + sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
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if (tcph + 1 > data_end)
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return;
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memcpy(tup.ipv6.saddr, &ipv6h->saddr, sizeof(tup.ipv6.saddr));
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memcpy(tup.ipv6.daddr, &ipv6h->daddr, sizeof(tup.ipv6.daddr));
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tup.ipv6.sport = tcph->source;
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tup.ipv6.dport = tcph->dest;
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sk = bpf_skc_lookup_tcp(ctx, &tup, sizeof(tup.ipv6),
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BPF_F_CURRENT_NETNS, 0);
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if (!sk)
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return;
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if (sk->state != BPF_TCP_LISTEN)
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goto release;
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seq_mss = gen_syncookie(data_end, sk, ipv6h, sizeof(*ipv6h),
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tcph);
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ret = bpf_tcp_check_syncookie(sk, ipv6h, sizeof(*ipv6h),
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tcph, sizeof(*tcph));
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break;
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default:
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return;
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}
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if (seq_mss > 0) {
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__u32 cookie = (__u32)seq_mss;
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__u32 mss = seq_mss >> 32;
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bpf_map_update_elem(&results, &key_gen, &cookie, 0);
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bpf_map_update_elem(&results, &key_mss, &mss, 0);
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}
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if (ret == 0) {
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__u32 cookie = bpf_ntohl(tcph->ack_seq) - 1;
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bpf_map_update_elem(&results, &key, &cookie, 0);
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}
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release:
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bpf_sk_release(sk);
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}
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SEC("clsact/check_syncookie")
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int check_syncookie_clsact(struct __sk_buff *skb)
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{
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check_syncookie(skb, (void *)(long)skb->data,
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(void *)(long)skb->data_end);
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return TC_ACT_OK;
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}
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SEC("xdp/check_syncookie")
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int check_syncookie_xdp(struct xdp_md *ctx)
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{
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check_syncookie(ctx, (void *)(long)ctx->data,
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(void *)(long)ctx->data_end);
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return XDP_PASS;
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}
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char _license[] SEC("license") = "GPL";
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