[PATCH 4.9 04/44] net: bridge: multicast: use rcu to access port list from br_multicast_start_querier

[Greg Kroah-Hartman]

From: Nikolay Aleksandrov <niko...@cumulusnetworks.com>

[ Upstream commit c5b493ce192bd7a4e7bd073b5685aad121eeef82 ]

br_multicast_start_querier() walks over the port list but it can be
called from a timer with only multicast_lock held which doesn't protect
the port list, so use RCU to walk over it.

Fixes: c83b8fab06fc ("bridge: Restart queries when last querier expires")
Signed-off-by: Nikolay Aleksandrov <niko...@cumulusnetworks.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/bridge/br_multicast.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1983,7 +1983,8 @@ static void br_multicast_start_querier(s
 
        __br_multicast_open(br, query);
 
-       list_for_each_entry(port, &br->port_list, list) {
+       rcu_read_lock();
+       list_for_each_entry_rcu(port, &br->port_list, list) {
                if (port->state == BR_STATE_DISABLED ||
                    port->state == BR_STATE_BLOCKING)
                        continue;
@@ -1995,6 +1996,7 @@ static void br_multicast_start_querier(s
                        br_multicast_enable(&port->ip6_own_query);
 #endif
        }
+       rcu_read_unlock();
 }
 
 int br_multicast_toggle(struct net_bridge *br, unsigned long val)