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-Url: https://git.stricted.de/?a=commitdiff_plain;h=d69bbf88c8d0;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

net: fix a race in dst_release()

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>
---

diff --git a/net/core/dst.c b/net/core/dst.c
index 2a1818065e12..e6dc77252fe9 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -306,7 +306,7 @@ void dst_release(struct dst_entry *dst)
 		if (unlikely(newrefcnt < 0))
 			net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
 					     __func__, dst, newrefcnt);
-		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt)
+		if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
 			call_rcu(&dst->rcu_head, dst_destroy_rcu);
 	}
 }