On 7/16/19 2:26 AM, Petar Penkov wrote:
> From: Petar Penkov <ppen...@google.com>
>
> This helper function allows BPF programs to try to generate SYN
> cookies, given a reference to a listener socket. The function works
> from XDP and with an skb context since bpf_skc_lookup_tcp can lookup a
> socket in both cases.
>
...
>
> +BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32,
> iph_len,
> + struct tcphdr *, th, u32, th_len)
> +{
> +#ifdef CONFIG_SYN_COOKIES
> + u32 cookie;
> + u16 mss;
> +
> + if (unlikely(th_len < sizeof(*th)))
You probably need to check that th_len == th->doff * 4
> + return -EINVAL;
> +
> + if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
> + return -EINVAL;
> +
> + if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
> + return -EINVAL;
> +
> + if (!th->syn || th->ack || th->fin || th->rst)
> + return -EINVAL;
> +
> + switch (sk->sk_family) {
This is strange, because a dual stack listener will have sk->sk_family set to
AF_INET6.
What really matters here is if the packet is IPv4 or IPv6.
So you need to look at iph->version instead.
Then look if the socket family allows this packet to be processed
(For example AF_INET6 sockets might prevent IPv4 packets, see sk->sk_ipv6only )
> + case AF_INET:
> + if (unlikely(iph_len < sizeof(struct iphdr)))
> + return -EINVAL;
> + mss = tcp_v4_get_syncookie(sk, iph, th, &cookie);
> + break;
> +
> +#if IS_BUILTIN(CONFIG_IPV6)
> + case AF_INET6:
> + if (unlikely(iph_len < sizeof(struct ipv6hdr)))
> + return -EINVAL;
> + mss = tcp_v6_get_syncookie(sk, iph, th, &cookie);
> + break;
> +#endif /* CONFIG_IPV6 */
> +
> + default:
> + return -EPROTONOSUPPORT;
> + }
> + if (mss <= 0)
> + return -ENOENT;
> +
