[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>

net/ipv4/igmp.c

@@ -897,6 +897,9 @@ int igmp_rcv(struct sk_buff *skb)
 		/* Is it our report looped back? */
 		if (((struct rtable*)skb->dst)->fl.iif == 0)
 			break;
+		/* 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:

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;