netdev - Re: [PATCH net-next v7 03/11] tcp: use drop reasons in cookie check for ipv4

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Message-ID: <CANn89iL-FH6jzoxhyKSMioj-zdBsHqNpR7YTGz8ytM=FZSGrug@mail.gmail.com>
Date: Wed, 21 Feb 2024 10:34:47 +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 v7 03/11] tcp: use drop reasons in cookie check
 for ipv4

On Wed, Feb 21, 2024 at 3:57 AM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> From: Jason Xing <kernelxing@...cent.com>
>
> Now it's time to use the prepared definitions to refine this part.
> Four reasons used might enough for now, I think.
>
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> --
> v6:
> Link: https://lore.kernel.org/netdev/20240215210922.19969-1-kuniyu@amazon.com/
> 1. Not use NOMEM because of MPTCP (Kuniyuki). I chose to use NO_SOCKET as
> an indicator which can be used as three kinds of cases to tell people that we're
> unable to get a valid one. It's a relatively general reason like what we did
> to TCP_FLAGS.
> Any better ideas/suggestions are welcome :)
>
> v5:
> Link: https://lore.kernel.org/netdev/CANn89i+iELpsoea6+C-08m6+=JkneEEM=nAj-28eNtcOCkwQjw@mail.gmail.com/
> Link: https://lore.kernel.org/netdev/632c6fd4-e060-4b8e-a80e-5d545a6c6b6c@kernel.org/
> 1. Use SKB_DROP_REASON_IP_OUTNOROUTES instead of introducing a new one (Eric, David)
> 2. Reuse SKB_DROP_REASON_NOMEM to handle failure of request socket allocation (Eric)
> 3. Reuse NO_SOCKET instead of introducing COOKIE_NOCHILD
> ---
>  net/ipv4/syncookies.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 38f331da6677..1028429c78a5 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -421,8 +421,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>                 if (IS_ERR(req))
>                         goto out;
>         }
> -       if (!req)
> +       if (!req) {
> +               SKB_DR_SET(reason, NO_SOCKET);
>                 goto out_drop;
> +       }
>
>         ireq = inet_rsk(req);
>
> @@ -434,8 +436,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>          */
>         RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(net, skb));
>
> -       if (security_inet_conn_request(sk, skb, req))
> +       if (security_inet_conn_request(sk, skb, req)) {
> +               SKB_DR_SET(reason, SECURITY_HOOK);
>                 goto out_free;
> +       }
>
>         tcp_ao_syncookie(sk, skb, req, AF_INET);
>
> @@ -452,8 +456,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>                            ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
>         security_req_classify_flow(req, flowi4_to_flowi_common(&fl4));
>         rt = ip_route_output_key(net, &fl4);
> -       if (IS_ERR(rt))
> +       if (IS_ERR(rt)) {
> +               SKB_DR_SET(reason, IP_OUTNOROUTES);
>                 goto out_free;
> +       }
>
>         /* Try to redo what tcp_v4_send_synack did. */
>         req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
> @@ -476,10 +482,12 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>         /* ip_queue_xmit() depends on our flow being setup
>          * Normal sockets get it right from inet_csk_route_child_sock()
>          */
> -       if (ret)
> +       if (ret) {
>                 inet_sk(ret)->cork.fl.u.ip4 = fl4;
> -       else
> +       } else {
> +               SKB_DR_SET(reason, NO_SOCKET);
>                 goto out_drop;
> +       }

You can avoid the else here

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index be88bf586ff9ffba2190a1fd60a1ed3ce5f73d06..d56b0e309cfc0a58dcd277881fe2b364ab3cc668
100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -475,8 +475,11 @@ struct sock *cookie_v4_check(struct sock *sk,
struct sk_buff *skb)
        /* ip_queue_xmit() depends on our flow being setup
         * Normal sockets get it right from inet_csk_route_child_sock()
         */
-       if (ret)
-               inet_sk(ret)->cork.fl.u.ip4 = fl4;
+       if (!ret) {
+               SKB_DR_SET(reason, NO_SOCKET);
+               goto out_drop;
+       }
+       inet_sk(ret)->cork.fl.u.ip4 = fl4;
 out:
        return ret;
 out_free: