[PATCH net-next v5 03/11] tcp: use drop reasons in cookie check for ipv4

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jason Xing <kerneljasonxing@gmail.com>
Date: Thu, 15 Feb 2024 09:20:19 +0800
> From: Jason Xing <kernelxing@tencent.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@tencent.com>
> --
> 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..aeb61c880fbd 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, NOMEM);

NOMEM is not appropriate when mptcp_subflow_init_cookie_req() fails.


>  		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);

This also seems wrong to me.

e.g. syn_recv_sock() could fail with sk_acceptq_is_full(sk),
then the listener is actually found.


>  		goto out_drop;
> +	}
>  out:
>  	return ret;
>  out_free:
> -- 
> 2.37.3
>