[Bridge] [PATCH net 2/2] net: bridge: multicast: fix MRD advertisement router port marking race

Nikolay Aleksandrov razor at blackwall.org
Sun Jul 11 09:56:29 UTC 2021

From: Nikolay Aleksandrov <nikolay at nvidia.com>

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

Cc: stable at vger.kernel.org
Cc: linus.luessing at c0d3.blue
Fixes: 4b3087c7e37f ("bridge: Snoop Multicast Router Advertisements")
Signed-off-by: Nikolay Aleksandrov <nikolay at nvidia.com>
 net/bridge/br_multicast.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 3bbbc6d7b7c3..d0434dc8c03b 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -3277,7 +3277,9 @@ static int br_ip4_multicast_mrd_rcv(struct net_bridge *br,
 	    igmp_hdr(skb)->type != IGMP_MRDISC_ADV)
 		return -ENOMSG;
+	spin_lock(&br->multicast_lock);
 	br_ip4_multicast_mark_router(br, port);
+	spin_unlock(&br->multicast_lock);
 	return 0;
@@ -3345,7 +3347,9 @@ static void br_ip6_multicast_mrd_rcv(struct net_bridge *br,
 	if (icmp6_hdr(skb)->icmp6_type != ICMPV6_MRDISC_ADV)
+	spin_lock(&br->multicast_lock);
 	br_ip6_multicast_mark_router(br, port);
+	spin_unlock(&br->multicast_lock);
 static int br_multicast_ipv6_rcv(struct net_bridge *br,

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