net: fix a race in dst_release()

d69bbf88 · Eric Dumazet <[email protected]> · 2015-11-09 17:51:23 -08:00

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 <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Commit: d69bbf88c8d0b367cf3e3a052f6daadf630ee566
Parents: 8c94ddbc

Changes

1 files changed · +1 −1

File	Status	Add	Del	Content
net/core/dst.c	modified	+1	−1	View file

net/core/dst.c

View file

diff --git a/net/core/dst.c b/net/core/dst.c
index 2a18180..e6dc772 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);
 	}
 }