netdev - Re: [PATCH net-next v4 4/5] tcp: directly drop skb in cookie check for ipv6

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Message-ID: <CANn89iKz7=1q7e8KY57Dn3ED7O=RCOfLxoHQKO4eNXnZa1OPWg@mail.gmail.com>
Date: Tue, 13 Feb 2024 16:30:13 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	dsahern@...nel.org, kuniyu@...zon.com, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4 4/5] tcp: directly drop skb in cookie check
 for ipv6

On Tue, Feb 13, 2024 at 2:42 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> From: Jason Xing <kernelxing@...cent.com>
>
> Like previous patch does, only moving skb drop logical code to
> cookie_v6_check() for later refinement.
>
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
>  net/ipv6/syncookies.c | 4 ++++
>  net/ipv6/tcp_ipv6.c   | 7 +++++--
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> index 6b9c69278819..ea0d9954a29f 100644
> --- a/net/ipv6/syncookies.c
> +++ b/net/ipv6/syncookies.c
> @@ -177,6 +177,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
>         struct sock *ret = sk;
>         __u8 rcv_wscale;
>         int full_space;
> +       SKB_DR(reason);
>
>         if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||
>             !th->ack || th->rst)
> @@ -256,10 +257,13 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
>         ireq->ecn_ok &= cookie_ecn_ok(net, dst);
>
>         ret = tcp_get_cookie_sock(sk, skb, req, dst);
> +       if (!ret)
> +               goto out_drop;
>  out:
>         return ret;
>  out_free:
>         reqsk_free(req);
>  out_drop:
> +       kfree_skb_reason(skb, reason);
>         return NULL;
>  }
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 57b25b1fc9d9..27639ffcae2f 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1653,8 +1653,11 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
>         if (sk->sk_state == TCP_LISTEN) {
>                 struct sock *nsk = tcp_v6_cookie_check(sk, skb);
>
> -               if (!nsk)
> -                       goto discard;
> +               if (!nsk) {
> +                       if (opt_skb)
> +                               __kfree_skb(opt_skb);
> +                       return 0;
> +               }
>
>                 if (nsk != sk) {
>                         if (tcp_child_process(sk, nsk, skb))
> --

or perhaps try to avoid duplication of these opt_skb tests/actions.

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 57b25b1fc9d9d529e3c53778ef09b65b1ac4c9d5..1ca4f11c3d6f3af2a0148f0e50dfea96b8ba3a53
100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1653,16 +1653,13 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
        if (sk->sk_state == TCP_LISTEN) {
                struct sock *nsk = tcp_v6_cookie_check(sk, skb);

-               if (!nsk)
-                       goto discard;
-
-               if (nsk != sk) {
+               if (nsk && nsk != sk) {
                        if (tcp_child_process(sk, nsk, skb))
                                goto reset;
-                       if (opt_skb)
-                               __kfree_skb(opt_skb);
-                       return 0;
                }
+               if (opt_skb)
+                       __kfree_skb(opt_skb);
+               return 0;
        } else
                sock_rps_save_rxhash(sk, skb);