bridge: multicast: add sanity check for query source addresses

MLD queries are supposed to have an IPv6 link-local source address
according to RFC2710, section 4 and RFC3810, section 5.1.14. This patch
adds a sanity check to ignore such broken MLD queries.

Without this check, such malformed MLD queries can result in a
denial of service: The queries are ignored by any MLD listener
therefore they will not respond with an MLD report. However,
without this patch these malformed MLD queries would enable the
snooping part in the bridge code, potentially shutting down the
according ports towards these hosts for multicast traffic as the
bridge did not learn about these listeners.

Reported-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index ef66365b7354da9f2fe2c4d87d2056d9a781f3c8..fb0e36fac668e29ceab3bb11ea4df47a83291e52 100644 (file)
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1235,6 +1235,12 @@ static int br_ip6_multicast_query(struct net_bridge *br,
            (port && port->state == BR_STATE_DISABLED))
                goto out;
 
+       /* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
+       if (!(ipv6_addr_type(&ip6h->saddr) & IPV6_ADDR_LINKLOCAL)) {
+               err = -EINVAL;
+               goto out;
+       }
+
        if (skb->len == sizeof(*mld)) {
                if (!pskb_may_pull(skb, sizeof(*mld))) {
                        err = -EINVAL;