linux-kernel - [ 025/135] bridge: fix NULL pointer deref of br_port_get

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Message-Id: <20131011193947.967604914@linuxfoundation.org>
Date:	Fri, 11 Oct 2013 12:38:26 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Hong Zhiguo <zhiguohong@...cent.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 025/135] bridge: fix NULL pointer deref of br_port_get_rcu

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

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

From: Hong Zhiguo <zhiguohong@...cent.com>

[ Upstream commit 716ec052d2280d511e10e90ad54a86f5b5d4dcc2 ]

The NULL deref happens when br_handle_frame is called between these
2 lines of del_nbp:
	dev->priv_flags &= ~IFF_BRIDGE_PORT;
	/* --> br_handle_frame is called at this time */
	netdev_rx_handler_unregister(dev);

In br_handle_frame the return of br_port_get_rcu(dev) is dereferenced
without check but br_port_get_rcu(dev) returns NULL if:
	!(dev->priv_flags & IFF_BRIDGE_PORT)

Eric Dumazet pointed out the testing of IFF_BRIDGE_PORT is not necessary
here since we're in rcu_read_lock and we have synchronize_net() in
netdev_rx_handler_unregister. So remove the testing of IFF_BRIDGE_PORT
and by the previous patch, make sure br_port_get_rcu is called in
bridging code.

Signed-off-by: Hong Zhiguo <zhiguohong@...cent.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/bridge/br_private.h |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -202,10 +202,7 @@ struct net_bridge_port
 
 static inline struct net_bridge_port *br_port_get_rcu(const struct net_device *dev)
 {
-	struct net_bridge_port *port =
-			rcu_dereference_rtnl(dev->rx_handler_data);
-
-	return br_port_exists(dev) ? port : NULL;
+	return rcu_dereference(dev->rx_handler_data);
 }
 
 static inline struct net_bridge_port *br_port_get_rtnl(const struct net_device *dev)


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