linux-kernel - [PATCH 3.8 42/81] bridge: fix NULL pointer deref of br_port_get

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Message-Id: <1383069882-11437-43-git-send-email-kamal@canonical.com>
Date:	Tue, 29 Oct 2013 11:04:03 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Hong Zhiguo <zhiguohong@...cent.com>,
	"David S. Miller" <davem@...emloft.net>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.8 42/81] bridge: fix NULL pointer deref of br_port_get_rcu

3.8.13.12 -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: Kamal Mostafa <kamal@...onical.com>
---
 net/bridge/br_private.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 688fc44..f56cd47 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -162,10 +162,7 @@ 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)
-- 
1.8.1.2

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