[PATCH net-next v5 04/11] tcp: directly drop skb in cookie check for ipv6

[Jason Xing <kerneljasonxing@gmail.com>]

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>
--
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   | 11 ++++-------
 2 files changed, 8 insertions(+), 7 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..1ca4f11c3d6f 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);
 
-- 
2.37.3