net: bridge: multicast: fix PIM hello router port marking race

stable inclusion
from linux-4.19.198
commit 2e70bf39b1a96b40ab13044729613a913b46cddd

--------------------------------

commit 04bef83a upstream.

When a PIM hello packet is received on a bridge port with multicast
snooping enabled, we mark it as a router port automatically, that
includes adding that port the router port list. The multicast lock
protects that list, but it is not acquired in the PIM message case
leading to a race condition, we need to take it to fix the race.

Cc: stable@vger.kernel.org
Fixes: 91b02d3d ("bridge: mcast: add router port on PIM hello message")
Signed-off-by: NNikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/bridge/br_multicast.c

@@ -1791,7 +1791,9 @@ static void br_multicast_pim(struct net_bridge *br,
 	    pim_hdr_type(pimhdr) != PIM_TYPE_HELLO)
 		return;
 
+	spin_lock(&br->multicast_lock);
 	br_multicast_mark_router(br, port);
+	spin_unlock(&br->multicast_lock);
 }
 
 static int br_multicast_ipv4_rcv(struct net_bridge *br,