Re: [PATCH net-next v6 04/11] tcp: directly drop skb in cookie check for ipv6

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jason Xing <kerneljasonxing@gmail.com>
Date: Mon, 19 Feb 2024 11:28:31 +0800
> From: Jason Xing <kernelxing@tencent.com>
> 
> Like previous patch does, only moving skb drop logical code to
> cookie_v6_check() for later refinement.
> 
> Signed-off-by: Jason Xing <kernelxing@tencent.com>
> --
> v6
> Link: https://lore.kernel.org/all/c987d2c79e4a4655166eb8eafef473384edb37fb.camel@redhat.com/
> Link: https://lore.kernel.org/all/CAL+tcoAgSjwsmFnDh_Gs9ZgMi-y5awtVx+4VhJPNRADjo7LLSA@mail.gmail.com/
> 1. take one case into consideration, behave like old days, or else it will trigger errors.
> 
> v5
> Link: https://lore.kernel.org/netdev/CANn89iKz7=1q7e8KY57Dn3ED7O=RCOfLxoHQKO4eNXnZa1OPWg@mail.gmail.com/
> 1. avoid duplication of these opt_skb tests/actions (Eric)
> ---
>  net/ipv6/syncookies.c | 4 ++++
>  net/ipv6/tcp_ipv6.c   | 7 +++----
>  2 files changed, 7 insertions(+), 4 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..4cfeedfb871f 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1653,12 +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 != sk) {
> +		if (nsk && nsk != sk) {
>  			if (tcp_child_process(sk, nsk, skb))
>  				goto reset;
> +		}
> +		if (!nsk || nsk != sk) {

!nsk is redundant, when nsk is NULL, nsk != sk is true.

We can keep the original nsk != sk check and call tcp_child_process()
only when nsk is not NULL:

---8<---
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 57b25b1fc9d9..0c180bb8187f 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1653,11 +1653,8 @@ 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 (tcp_child_process(sk, nsk, skb))
+			if (nsk && tcp_child_process(sk, nsk, skb))
 				goto reset;
 			if (opt_skb)
 				__kfree_skb(opt_skb);
---8<---