On Thu, Dec 14, 2023 at 4:56 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
>
> We will support arbitrary SYN Cookie with BPF.
>
> If BPF prog validates ACK and kfunc allocates a reqsk, it will
> be carried to TCP stack as skb->sk with req->syncookie 1. Also,
> the reqsk has its listener as req->rsk_listener with no refcnt
> taken.
>
> When the TCP stack looks up a socket from the skb, we steal
> inet_reqsk(skb->sk)->rsk_listener in skb_steal_sock() so that
> the skb will be processed in cookie_v[46]_check() with the
> listener.
>
> Note that we do not clear skb->sk and skb->destructor so that we
> can carry the reqsk to cookie_v[46]_check().
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> ---
> include/net/request_sock.h | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/request_sock.h b/include/net/request_sock.h
> index 26c630c40abb..8839133d6f6b 100644
> --- a/include/net/request_sock.h
> +++ b/include/net/request_sock.h
> @@ -101,10 +101,21 @@ static inline struct sock *skb_steal_sock(struct sk_buff *skb,
> }
>
> *prefetched = skb_sk_is_prefetched(skb);
> - if (*prefetched)
> + if (*prefetched) {
> +#if IS_ENABLED(CONFIG_SYN_COOKIES)
> + if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) {
> + struct request_sock *req = inet_reqsk(sk);
> +
> + *refcounted = false;
> + sk = req->rsk_listener;
> + req->rsk_listener = NULL;
I am not sure about interactions with MPTCP.
I would be nice to have their feedback.
> + return sk;
> + }
> +#endif
> *refcounted = sk_is_refcounted(sk);
> - else
> + } else {
> *refcounted = true;
> + }
>
> skb->destructor = NULL;
> skb->sk = NULL;
> --
> 2.30.2
>
