bridge: fix rcu dereference outside of rcu_read_lock

Alternative solution for problem found by Linux Driver Verification
project (linuxtesting.org).

As it noted in the comment before the br_handle_frame_finish
function, this function should be called under rcu_read_lock.

The problem callgraph:
br_dev_xmit -> br_nf_pre_routing_finish_bridge_slow ->
 -> br_handle_frame_finish -> br_port_get_rcu -> rcu_dereference

And in this case there is no read-lock section.

Reported-by: Denis Efremov <yefremov.denis@gmail.com>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 32211fa5b506..070e8a68cfc6 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -31,9 +31,11 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
         struct net_bridge_mdb_entry *mdst;
         struct br_cpu_netstats *brstats = this_cpu_ptr(br->stats);
 
+        rcu_read_lock();
 #ifdef CONFIG_BRIDGE_NETFILTER
         if (skb->nf_bridge && (skb->nf_bridge->mask & BRNF_BRIDGED_DNAT)) {
                 br_nf_pre_routing_finish_bridge_slow(skb);
+                rcu_read_unlock();
                 return NETDEV_TX_OK;
         }
 #endif
@@ -48,7 +50,6 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
         skb_reset_mac_header(skb);
         skb_pull(skb, ETH_HLEN);
 
-        rcu_read_lock();
         if (is_broadcast_ether_addr(dest))
                 br_flood_deliver(br, skb);
         else if (is_multicast_ether_addr(dest)) {