From: Eric Dumazet <edumazet@google.com>
Date: Tue, 10 Nov 2015 01:51:23 +0000 (-0800)
Subject: net: fix a race in dst_release()
X-Git-Tag: v4.1.12-92~201^2~54
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=ae406e508beb6067a39aabad2a6344a44368f18d;p=users%2Fjedix%2Flinux-maple.git

net: fix a race in dst_release()

Orabug: 22623844

[ Upstream commit d69bbf88c8d0b367cf3e3a052f6daadf630ee566 ]

Only cpu seeing dst refcount going to 0 can safely
dereference dst->flags.

Otherwise an other cpu might already have freed the dst.

Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Reported-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit e6fac8c7fff3d816729ad16327837ba3216d48c9)
Signed-off-by: Dan Duval <dan.duval@oracle.com>
---

diff --git a/net/core/dst.c b/net/core/dst.c
index e956ce6d13782..f8db4032d45a4 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -285,7 +285,7 @@ void dst_release(struct dst_entry *dst)
 
 		newrefcnt = atomic_dec_return(&dst->__refcnt);
 		WARN_ON(newrefcnt < 0);
-		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt)
+		if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
 			call_rcu(&dst->rcu_head, dst_destroy_rcu);
 	}
 }