inet: fix possible panic in reqsk_queue_unlink()

[ 3897.923145] BUG: unable to handle kernel NULL pointer dereference at
 0000000000000080
[ 3897.931025] IP: [<ffffffffa9f27686>] reqsk_timer_handler+0x1a6/0x243

There is a race when reqsk_timer_handler() and tcp_check_req() call
inet_csk_reqsk_queue_unlink() on the same req at the same time.

Before commit fa76ce7328b2 ("inet: get rid of central tcp/dccp listener
timer"), listener spinlock was held and race could not happen.

To solve this bug, we change reqsk_queue_unlink() to not assume req
must be found, and we return a status, to conditionally release a
refcount on the request sock.

This also means tcp_check_req() in non fastopen case might or not
consume req refcount, so tcp_v6_hnd_req() & tcp_v4_hnd_req() have
to properly handle this.

(Same remark for dccp_check_req() and its callers)

inet_csk_reqsk_queue_drop() is now too big to be inlined, as it is
called 4 times in tcp and 3 times in dccp.

Fixes: fa76ce7328b2 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 1 insertions, 37 deletions

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 7b5887cd1172..48a815823587 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -279,12 +279,6 @@ static inline void inet_csk_reqsk_queue_add(struct sock *sk,
 void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
 				   unsigned long timeout);
 
-static inline void inet_csk_reqsk_queue_removed(struct sock *sk,
-						struct request_sock *req)
-{
-	reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
-}
-
 static inline void inet_csk_reqsk_queue_added(struct sock *sk,
 					      const unsigned long timeout)
 {
@@ -306,19 +300,7 @@ static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)
 	return reqsk_queue_is_full(&inet_csk(sk)->icsk_accept_queue);
 }
 
-static inline void inet_csk_reqsk_queue_unlink(struct sock *sk,
-					       struct request_sock *req)
-{
-	reqsk_queue_unlink(&inet_csk(sk)->icsk_accept_queue, req);
-}
-
-static inline void inet_csk_reqsk_queue_drop(struct sock *sk,
-					     struct request_sock *req)
-{
-	inet_csk_reqsk_queue_unlink(sk, req);
-	inet_csk_reqsk_queue_removed(sk, req);
-	reqsk_put(req);
-}
+void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
 
 void inet_csk_destroy_sock(struct sock *sk);
 void inet_csk_prepare_forced_close(struct sock *sk);
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index fe41f3ceb008..9f4265ce8892 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -212,24 +212,6 @@ static inline int reqsk_queue_empty(struct request_sock_queue *queue)
 	return queue->rskq_accept_head == NULL;
 }
 
-static inline void reqsk_queue_unlink(struct request_sock_queue *queue,
-				      struct request_sock *req)
-{
-	struct listen_sock *lopt = queue->listen_opt;
-	struct request_sock **prev;
-
-	spin_lock(&queue->syn_wait_lock);
-
-	prev = &lopt->syn_table[req->rsk_hash];
-	while (*prev != req)
-		prev = &(*prev)->dl_next;
-	*prev = req->dl_next;
-
-	spin_unlock(&queue->syn_wait_lock);
-	if (del_timer(&req->rsk_timer))
-		reqsk_put(req);
-}
-
 static inline void reqsk_queue_add(struct request_sock_queue *queue,
 				   struct request_sock *req,
 				   struct sock *parent,