[PATCH net/next] bridge:Add rcu read lock when delete br port

[<lichunhe@huawei.com>]

From: Chunhe Li <lichunhe@huawei.com>

In the br_hanle_frame function has a bug, when the bridge receive packets
which go througth the br_handle_frame, get the net_bridge_port pointer "p",
but don't check NULL pointer to use it. If somebody delete the bridge port
at the same time, will call a NULL pointer, trigger kernel panic. I see the
del_nbp comments, call del_nbp should via RCU, but the caller don't do this.

following steps will make bug happened
1.start vm and add the vm interface to a bridge br0,for example,
brctl addbr br0 tap0

2.configuer vm interface and br0 same ip subnet, vm ping br0.

3.add and delete the vm interface port for endless loop.

Signed-off-by: Chunhe Li <lichunhe@huawei.com>
---
 net/bridge/br_if.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 3eca3fd..91c611d 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -274,9 +274,11 @@ void br_dev_delete(struct net_device *dev, struct list_head *head)
 	struct net_bridge *br = netdev_priv(dev);
 	struct net_bridge_port *p, *n;
 
+	rcu_read_lock();
 	list_for_each_entry_safe(p, n, &br->port_list, list) {
 		del_nbp(p);
 	}
+	rcu_read_unlock();
 
 	br_fdb_delete_by_port(br, NULL, 1);
 
@@ -550,7 +552,9 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
 	 * there still maybe an alternate path for netconsole to use;
 	 * therefore there is no reason for a NETDEV_RELEASE event.
 	 */
+	rcu_read_lock();
 	del_nbp(p);
+	rcu_read_unlock();
 
 	spin_lock_bh(&br->lock);
 	changed_addr = br_stp_recalculate_bridge_id(br);
-- 
1.9.2.0