ipv6: don't accept node local multicast traffic from the wire

Erik Hugne's errata proposal (Errata ID: 3480) to RFC4291 has been
verified: http://www.rfc-editor.org/errata_search.php?eid=3480

We have to check for pkt_type and loopback flag because either the
packets are allowed to travel over the loopback interface (in which case
pkt_type is PACKET_HOST and IFF_LOOPBACK flag is set) or they travel
over a non-loopback interface back to us (in which case PACKET_TYPE is
PACKET_LOOPBACK and IFF_LOOPBACK flag is not set).

Cc: Erik Hugne <erik.hugne@ericsson.com>
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_input.c

@@ -118,6 +118,18 @@ int ipv6_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt
 	    ipv6_addr_loopback(&hdr->daddr))
 		goto err;
 
+	/* RFC4291 Errata ID: 3480
+	 * Interface-Local scope spans only a single interface on a
+	 * node and is useful only for loopback transmission of
+	 * multicast.  Packets with interface-local scope received
+	 * from another node must be discarded.
+	 */
+	if (!(skb->pkt_type == PACKET_LOOPBACK ||
+	      dev->flags & IFF_LOOPBACK) &&
+	    ipv6_addr_is_multicast(&hdr->daddr) &&
+	    IPV6_ADDR_MC_SCOPE(&hdr->daddr) == 1)
+		goto err;
+
 	/* RFC4291 2.7
 	 * Nodes must not originate a packet to a multicast address whose scope
 	 * field contains the reserved value 0; if such a packet is received, it