Subject: [PATCH 05/18] inet: fix potential deadlock in reqsk_queue_unlink()

From: Eric Dumazet <[email-masked]>
Date: Thu, 13 Aug 2015 15:44:51 -0700

[ Upstream commit 83fccfc3940c4a2db90fd7e7079f5b465cd8c6af ]

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 <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/ipv4/inet_connection_sock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index b27fc40..e664706 100644
--- 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;
 }
-- 
1.7.10.4