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Subject[PATCH 3.16.y-ckt 012/126] net: fix a race in dst_release()
Date
3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

commit d69bbf88c8d0b367cf3e3a052f6daadf630ee566 upstream.

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>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.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 a028409ee438..a80e92346b9b 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);
}
}

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