inet: fix potential deadlock in reqsk_queue_unlink()

When replacing del_timer() with del_timer_sync(), I introduced
a deadlock condition :

reqsk_queue_unlink() is called from inet_csk_reqsk_queue_drop()

inet_csk_reqsk_queue_drop() can be called from many contexts,
one being the timer handler itself (reqsk_timer_handler()).

In this case, del_timer_sync() loops forever.

Simple fix is to test if timer is pending.

Fixes: 2235f2ac75fd ("inet: fix races with reqsk timers")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 83fccfc3940c4a2db90fd7e7079f5b465cd8c6af)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index b27fc401c6a9a971970864b04feb45c674233194..e664706b350cd629281301b6abdb11a8a0b1bd11 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -584,7 +584,7 @@ static bool reqsk_queue_unlink(struct request_sock_queue *queue,
        }
 
        spin_unlock(&queue->syn_wait_lock);
-       if (del_timer_sync(&req->rsk_timer))
+       if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
                reqsk_put(req);
        return found;
 }