Re: [PATCH net-next v9 02/10] tcp: directly drop skb in cookie check for ipv4

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jason Xing <kerneljasonxing@gmail.com>
Date: Fri, 23 Feb 2024 18:28:43 +0800
> From: Jason Xing <kernelxing@tencent.com>
> 
> Only move the skb drop from tcp_v4_do_rcv() to cookie_v4_check() itself,
> no other changes made. It can help us refine the specific drop reasons
> later.
> 
> Signed-off-by: Jason Xing <kernelxing@tencent.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Reviewed-by: David Ahern <dsahern@kernel.org>
> --
> v9
> Link: https://lore.kernel.org/netdev/c5640fc4-16dc-4058-97c6-bd84bae4fda1@kernel.org/
> 1. add reviewed-by tag (David)
> 
> v8
> Link: https://lore.kernel.org/netdev/CANn89i+foA-AW3KCNw232eCC5GDi_3O0JG-mpvyiQJYuxKxnRA@mail.gmail.com/
> 1. add reviewed-by tag (Eric)
> 
> v7
> Link: https://lore.kernel.org/all/20240219041350.95304-1-kuniyu@amazon.com/
> 1. add reviewed-by tag (Kuniyuki)
> ---
>  net/ipv4/syncookies.c | 4 ++++
>  net/ipv4/tcp_ipv4.c   | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index be88bf586ff9..38f331da6677 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -408,6 +408,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>  	struct rtable *rt;
>  	__u8 rcv_wscale;
>  	int full_space;
> +	SKB_DR(reason);
>  
>  	if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||
>  	    !th->ack || th->rst)
> @@ -477,10 +478,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
>  	 */
>  	if (ret)
>  		inet_sk(ret)->cork.fl.u.ip4 = fl4;
> +	else
> +		goto out_drop;

nit: It would be nice to use the same style with IPv6 change.

	if (!ret)
		goto out_drop;

	inet_sk(ret)->cork.fl.u.ip4 = fl4;

Otherwise looks good.

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>


>  out:
>  	return ret;
>  out_free:
>  	reqsk_free(req);
>  out_drop:
> +	kfree_skb_reason(skb, reason);
>  	return NULL;
>  }
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 0c50c5a32b84..0a944e109088 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1915,7 +1915,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
>  		struct sock *nsk = tcp_v4_cookie_check(sk, skb);
>  
>  		if (!nsk)
> -			goto discard;
> +			return 0;
>  		if (nsk != sk) {
>  			if (tcp_child_process(sk, nsk, skb)) {
>  				rsk = nsk;
> -- 
> 2.37.3