[PATCH net-next v8 05/10] tcp: use drop reasons in cookie check for ipv6

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

Like what I did to ipv4 mode, refine this part: adding more drop
reasons for better tracing.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
--
v8
Link: https://lore.kernel.org/netdev/CANn89i+b+bYqX0aVv9KtSm=nLmEQznamZmqaOzfqtJm_ux9JBw@mail.gmail.com/
1. add reviewed-by tag (Eric)

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.

v5:
Link: https://lore.kernel.org/netdev/CANn89i+iELpsoea6+C-08m6+=JkneEEM=nAj-28eNtcOCkwQjw@mail.gmail.com/
1. Reuse SKB_DROP_REASON_NOMEM to handle failure of request socket allocation (Eric)
2. Reuse NO_SOCKET instead of introducing COOKIE_NOCHILD
3. Reuse IP_OUTNOROUTES instead of INVALID_DST (Eric)
---
 net/ipv6/syncookies.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index ea0d9954a29f..8bad0a44a0a6 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -190,16 +190,20 @@ struct sock *cookie_v6_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);
 
 	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
 	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
 
-	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;
+	}
 
 	if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
 	    np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
@@ -236,8 +240,10 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		security_req_classify_flow(req, flowi6_to_flowi_common(&fl6));
 
 		dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p);
-		if (IS_ERR(dst))
+		if (IS_ERR(dst)) {
+			SKB_DR_SET(reason, IP_OUTNOROUTES);
 			goto out_free;
+		}
 	}
 
 	req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
@@ -257,8 +263,10 @@ 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)
+	if (!ret) {
+		SKB_DR_SET(reason, NO_SOCKET);
 		goto out_drop;
+	}
 out:
 	return ret;
 out_free:
-- 
2.37.3