netdev - [PATCH net] net: fix a race in dst

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Message-ID: <1447120283.17135.64.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 09 Nov 2015 17:51:23 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Greg Thelen <gthelen@...gle.com>
Subject: [PATCH net] net: fix a race in dst_release()

From: Eric Dumazet <edumazet@...gle.com>

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@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dst.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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);
 	}
 }


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