From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date: Fri, 13 Oct 2023 15:04:28 -0700
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 514f1a4abdee..b1dd415863ff 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -317,6 +317,37 @@ struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
> }
> EXPORT_SYMBOL_GPL(cookie_tcp_reqsk_alloc);
>
> +#if IS_ENABLED(CONFIG_CGROUP_BPF) && IS_ENABLED(CONFIG_SYN_COOKIES)
> +int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
> +{
> + struct bpf_sock_ops_kern sock_ops;
> +
> + memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
> +
> + sock_ops.op = BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB;
> + sock_ops.sk = req_to_sk(req);
> + sock_ops.args[0] = tcp_rsk(req)->snt_isn;
> +
> + bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
> +
> + if (BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk))
> + goto err;
> +
> + if (!sock_ops.replylong[0])
> + goto err;
I noticed this test is insufficient to check valid MSS.
I'll use msstab[0] as the minimum valid MSS in v2.
---8<---
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 22353a9af52d..4af165fd48f9 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -287,6 +287,7 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
struct bpf_sock_ops_kern sock_ops;
struct net *net = sock_net(sk);
u32 options;
+ u16 min_mss;
if (tcp_opt->saw_tstamp) {
if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps))
@@ -307,7 +308,8 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
if (BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk))
goto err;
- if (!sock_ops.replylong[0])
+ min_mss = skb->protocol == htons(ETH_P_IP) ? msstab[0] : IPV6_MIN_MTU - 60;
+ if (sock_ops.replylong[0] < min_mss)
goto err;
options = sock_ops.replylong[1];
---8<---
> +
> + __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
> +
> + return sock_ops.replylong[0];
> +
> +err:
> + __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(bpf_skops_cookie_check);
> +#endif
> +
> /* On input, sk is a listener.
> * Output is listener if incoming packet would not create a child
> * NULL if memory could not be allocated.
