tcp: Clean up goto labels in cookie_v[46]_check().

We will support arbitrary SYN Cookie with BPF, and then reqsk
will be preallocated before cookie_v[46]_check().

Depending on how validation fails, we send RST or just drop skb.

To make the error handling easier, let's clean up goto labels.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20231129022924.96156-4-kuniyu@amazon.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/syncookies.c

@@ -376,11 +376,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	if (!cookie_timestamp_decode(net, &tcp_opt))
 		goto out;
 
-	ret = NULL;
 	req = cookie_tcp_reqsk_alloc(&tcp_request_sock_ops,
 				     &tcp_request_sock_ipv4_ops, sk, skb);
 	if (!req)
-		goto out;
+		goto out_drop;
 
 	ireq = inet_rsk(req);
 	treq = tcp_rsk(req);
@@ -415,10 +414,8 @@ 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)) {
-		reqsk_free(req);
-		goto out;
-	}
+	if (security_inet_conn_request(sk, skb, req))
+		goto out_free;
 
 	req->num_retrans = 0;
 
@@ -435,10 +432,8 @@ 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)) {
-		reqsk_free(req);
-		goto out;
-	}
+	if (IS_ERR(rt))
+		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);
@@ -462,5 +457,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	 */
 	if (ret)
 		inet_sk(ret)->cork.fl.u.ip4 = fl4;
-out:	return ret;
+out:
+	return ret;
+out_free:
+	reqsk_free(req);
+out_drop:
+	return NULL;
 }

net/ipv6/syncookies.c

@@ -172,11 +172,10 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	if (!cookie_timestamp_decode(net, &tcp_opt))
 		goto out;
 
-	ret = NULL;
 	req = cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops,
 				     &tcp_request_sock_ipv6_ops, sk, skb);
 	if (!req)
-		goto out;
+		goto out_drop;
 
 	ireq = inet_rsk(req);
 	treq = tcp_rsk(req);
@@ -269,5 +268,6 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	return ret;
 out_free:
 	reqsk_free(req);
+out_drop:
 	return NULL;
 }