[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, 4 insertions, 1 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index c04607b49212..4a195c724f01 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -897,7 +897,10 @@ int igmp_rcv(struct sk_buff *skb)
                 /* Is it our report looped back? */
                 if (((struct rtable*)skb->dst)->fl.iif == 0)
                         break;
-                igmp_heard_report(in_dev, ih->group);
+                /* don't rely on MC router hearing unicast reports */
+                if (skb->pkt_type == PACKET_MULTICAST ||
+                    skb->pkt_type == PACKET_BROADCAST)
+                        igmp_heard_report(in_dev, ih->group);
                 break;
         case IGMP_PIM:
 #ifdef CONFIG_IP_PIMSM_V1