From: Eric Dumazet <edumazet@google.com>
Date: Thu, 13 Aug 2015 22:44:51 +0000 (-0700)
Subject: inet: fix potential deadlock in reqsk_queue_unlink()
X-Git-Tag: firefly_0821_release~176^2~1254^2~11
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=83fccfc3940c4a2db90fd7e7079f5b465cd8c6af;p=firefly-linux-kernel-4.4.55.git

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>
---

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 05e3145f7dc3..134957159c27 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -593,7 +593,7 @@ 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;
 }