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Subject[PATCH] 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>
---
net/bridge/br_device.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 3334845..8a3b50f 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)) {
--
1.7.10.4


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