[PATCH 4.1 20/95] net: fix a race in dst_release()

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/core/dst.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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);
 	}
 }


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