tcp: free request sock directly upon TFO or syncookies error

Since the request socket is created locally, it'd make more sense to
use reqsk_free() instead of reqsk_put() in TFO and syncookies' error
path.

However, tcp_get_cookie_sock() may set ->rsk_refcnt before freeing the
socket; tcp_conn_request() may also have non-null ->rsk_refcnt because
of tcp_try_fastopen(). In both cases 'req' hasn't been exposed
to the outside world and is safe to free immediately, but that'd
trigger the WARN_ON_ONCE in reqsk_free().

Define __reqsk_free() for these situations where we know nobody's
referencing the socket, even though ->rsk_refcnt might be non-null.
Now we can consolidate the error path of tcp_get_cookie_sock() and
tcp_conn_request().
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/request_sock.h

@@ -106,10 +106,8 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener,
 	return req;
 }
 
-static inline void reqsk_free(struct request_sock *req)
+static inline void __reqsk_free(struct request_sock *req)
 {
-	WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
-
 	req->rsk_ops->destructor(req);
 	if (req->rsk_listener)
 		sock_put(req->rsk_listener);
@@ -117,6 +115,12 @@ static inline void reqsk_free(struct request_sock *req)
 	kmem_cache_free(req->rsk_ops->slab, req);
 }
 
+static inline void reqsk_free(struct request_sock *req)
+{
+	WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
+	__reqsk_free(req);
+}
+
 static inline void reqsk_put(struct request_sock *req)
 {
 	if (refcount_dec_and_test(&req->rsk_refcnt))

net/ipv4/syncookies.c

@@ -216,16 +216,15 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 		refcount_set(&req->rsk_refcnt, 1);
 		tcp_sk(child)->tsoffset = tsoff;
 		sock_rps_save_rxhash(child, skb);
-		if (!inet_csk_reqsk_queue_add(sk, req, child)) {
+		if (inet_csk_reqsk_queue_add(sk, req, child))
+			return child;
+
 		bh_unlock_sock(child);
 		sock_put(child);
-			child = NULL;
-			reqsk_put(req);
-		}
-	} else {
-		reqsk_free(req);
 	}
-	return child;
+	__reqsk_free(req);
+
+	return NULL;
 }
 EXPORT_SYMBOL(tcp_get_cookie_sock);
 

net/ipv4/tcp_input.c

@@ -6502,8 +6502,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			reqsk_fastopen_remove(fastopen_sk, req, false);
 			bh_unlock_sock(fastopen_sk);
 			sock_put(fastopen_sk);
-			reqsk_put(req);
-			goto drop;
+			goto drop_and_free;
 		}
 		sk->sk_data_ready(sk);
 		bh_unlock_sock(fastopen_sk);
@@ -6527,7 +6526,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 drop_and_release:
 	dst_release(dst);
 drop_and_free:
-	reqsk_free(req);
+	__reqsk_free(req);
 drop:
 	tcp_listendrop(sk);
 	return 0;