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