bridge: Use IPv6 link-local address for multicast listener queries

Currently the bridge multicast snooping feature periodically issues
IPv6 general multicast listener queries to sense the absence of a
listener.

For this, it uses :: as its source address - however RFC 2710 requires:
"To be valid, the Query message MUST come from a link-local IPv6 Source
Address". Current Linux kernel versions seem to follow this requirement
and ignore our bogus MLD queries.

With this commit a link local address from the bridge interface is being
used to issue the MLD query, resulting in other Linux devices which are
multicast listeners in the network to respond with a MLD response (which
was not the case before).

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index c1f24e4d0820..030a002ff8ee 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -445,7 +445,8 @@ static struct sk_buff *br_ip6_multicast_alloc_query(struct net_bridge *br,
         ip6h->payload_len = htons(8 + sizeof(*mldq));
         ip6h->nexthdr = IPPROTO_HOPOPTS;
         ip6h->hop_limit = 1;
-        ipv6_addr_set(&ip6h->saddr, 0, 0, 0, 0);
+        ipv6_dev_get_saddr(dev_net(br->dev), br->dev, &ip6h->daddr, 0,
+                           &ip6h->saddr);
         ipv6_addr_set(&ip6h->daddr, htonl(0xff020000), 0, 0, htonl(1));
         ipv6_eth_mc_map(&ip6h->daddr, eth->h_dest);