Linux Ethernet Bridging - Mar 2014 - [Bridge] [PATCHv2 2/2] bridge: multicast: enable snooping on general queries only

General IGMP and MLD queries are supposed to have the multicast
link-local all-nodes address as their destination according to RFC2236
section 9, RFC3376 section 4.1.12/9.1, RFC2710 section 8 and RFC3810
section 5.1.15.

Without this check, such malformed IGMP/MLD queries can result in a
denial of service: The queries are ignored by most IGMP/MLD listeners
therefore they will not respond with an IGMP/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 at redhat.com>
Signed-off-by: Linus L?ssing <linus.luessing at web.de>
---
v2: simplified is_general_query variable assignment (thanks Cong!)


 net/bridge/br_multicast.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index fb0e36f..e56bae4 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1181,6 +1181,14 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 			    IGMPV3_MRC(ih3->code) * (HZ / IGMP_TIMER_SCALE) : 1;
 	}
 
+	/* RFC2236+RFC3376 (IGMPv2+IGMPv3) require the multicast link layer
+	 * all-systems destination addresses (224.0.0.1) for general queries
+	 */
+	if (!group && iph->daddr != htonl(INADDR_ALLHOSTS_GROUP)) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	br_multicast_query_received(br, port, &br->ip4_querier,
!!iph->saddr,
 				    max_delay);
 
@@ -1228,6 +1236,7 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	unsigned long max_delay;
 	unsigned long now = jiffies;
 	const struct in6_addr *group = NULL;
+	bool is_general_query;
 	int err = 0;
 
 	spin_lock(&br->multicast_lock);
@@ -1262,6 +1271,16 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 		max_delay = max(msecs_to_jiffies(mldv2_mrc(mld2q)), 1UL);
 	}
 
+	is_general_query = group && ipv6_addr_any(group);
+
+	/* RFC2710+RFC3810 (MLDv1+MLDv2) require the multicast link layer
+	 * all-nodes destination address (ff02::1) for general queries
+	 */
+	if (is_general_query &&
!ipv6_addr_is_ll_all_nodes(&ip6h->daddr)) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	br_multicast_query_received(br, port, &br->ip6_querier,
 				    !ipv6_addr_any(&ip6h->saddr), max_delay);
 
-- 
1.7.10.4

Without this check someone could easily create a denial of service
by injecting multicast-specific queries to enable the bridge
snooping part if no real querier issuing periodic general queries
is present on the link which would result in the bridge wrongly
shutting down ports for multicast traffic as the bridge did not learn
about these listeners.

With this patch the snooping code is enabled upon receiving valid,
general queries only.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
---
v2: unchanged

 net/bridge/br_multicast.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index e56bae4..93067ec 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1127,9 +1127,10 @@ static void br_multicast_query_received(struct net_bridge
*br,
 					struct net_bridge_port *port,
 					struct bridge_mcast_querier *querier,
 					int saddr,
+					bool is_general_query,
 					unsigned long max_delay)
 {
-	if (saddr)
+	if (saddr && is_general_query)
 		br_multicast_update_querier_timer(br, querier, max_delay);
 	else if (timer_pending(&querier->timer))
 		return;
@@ -1190,7 +1191,7 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 	}
 
 	br_multicast_query_received(br, port, &br->ip4_querier,
!!iph->saddr,
-				    max_delay);
+				    !group, max_delay);
 
 	if (!group)
 		goto out;
@@ -1282,7 +1283,8 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	}
 
 	br_multicast_query_received(br, port, &br->ip6_querier,
-				    !ipv6_addr_any(&ip6h->saddr), max_delay);
+				    !ipv6_addr_any(&ip6h->saddr),
+				    is_general_query, max_delay);
 
 	if (!group)
 		goto out;
-- 
1.7.10.4

Without this check someone could easily create a denial of service
by injecting multicast-specific queries to enable the bridge
snooping part if no real querier issuing periodic general queries
is present on the link which would result in the bridge wrongly
shutting down ports for multicast traffic as the bridge did not learn
about these listeners.

With this patch the snooping code is enabled upon receiving valid,
general queries only.

Signed-off-by: Linus L?ssing <linus.luessing at web.de>
---
v2: unchanged

 net/bridge/br_multicast.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index e56bae4..93067ec 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1127,9 +1127,10 @@ static void br_multicast_query_received(struct net_bridge
*br,
 					struct net_bridge_port *port,
 					struct bridge_mcast_querier *querier,
 					int saddr,
+					bool is_general_query,
 					unsigned long max_delay)
 {
-	if (saddr)
+	if (saddr && is_general_query)
 		br_multicast_update_querier_timer(br, querier, max_delay);
 	else if (timer_pending(&querier->timer))
 		return;
@@ -1190,7 +1191,7 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 	}
 
 	br_multicast_query_received(br, port, &br->ip4_querier,
!!iph->saddr,
-				    max_delay);
+				    !group, max_delay);
 
 	if (!group)
 		goto out;
@@ -1282,7 +1283,8 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	}
 
 	br_multicast_query_received(br, port, &br->ip6_querier,
-				    !ipv6_addr_any(&ip6h->saddr), max_delay);
+				    !ipv6_addr_any(&ip6h->saddr),
+				    is_general_query, max_delay);
 
 	if (!group)
 		goto out;
-- 
1.7.10.4

From: Linus L?ssing <linus.luessing at web.de>
Date: Mon, 10 Mar 2014 22:25:24 +0100
> General IGMP and MLD queries are supposed to have the multicast
> link-local all-nodes address as their destination according to RFC2236
> section 9, RFC3376 section 4.1.12/9.1, RFC2710 section 8 and RFC3810
> section 5.1.15.
> 
> Without this check, such malformed IGMP/MLD queries can result in a
> denial of service: The queries are ignored by most IGMP/MLD listeners
> therefore they will not respond with an IGMP/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 at redhat.com>
> Signed-off-by: Linus L?ssing <linus.luessing at web.de>
Applied.

On Mon, 2014-03-10 at 22:25 +0100, Linus L?ssing wrote:
> General IGMP and MLD queries are supposed to have the multicast
> link-local all-nodes address as their destination according to RFC2236
> section 9, RFC3376 section 4.1.12/9.1, RFC2710 section 8 and RFC3810
> section 5.1.15.
[...]

That reminds me, shouldn't we also check this in igmp_rcv()?

Ben.

-- 
Ben Hutchings
Any sufficiently advanced bug is indistinguishable from a feature.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 811 bytes
Desc: This is a digitally signed message part
URL:
<http://lists.linuxfoundation.org/pipermail/bridge/attachments/20140312/59e06910/attachment.sig>