[IGMP]: workaround for IGMP v1/v2 bug

From: David Stevens <dlstevens@us.ibm.com>

As explained at:

	http://www.cs.ucsb.edu/~krishna/igmp_dos/

With IGMP version 1 and 2 it is possible to inject a unicast
report to a client which will make it ignore multicast
reports sent later by the router.

The fix is to only accept the report if is was sent to a
multicast or unicast address.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index f15e04ad026e..fd939da090c4 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1231,6 +1231,11 @@ int igmp6_event_report(struct sk_buff *skb)
         if (skb->pkt_type == PACKET_LOOPBACK)
                 return 0;
 
+        /* send our report if the MC router may not have heard this report */
+        if (skb->pkt_type != PACKET_MULTICAST &&
+            skb->pkt_type != PACKET_BROADCAST)
+                return 0;
+
         if (!pskb_may_pull(skb, sizeof(struct in6_addr)))
                 return -EINVAL;