ipv6: Drop packets for loopback address from outside of the box.

[ Based upon original report and patch by Karsten Keil.  Karsten
  has verified that this fixes the TAHI test case "ICMPv6 test
  v6LC.5.1.2 Part F". -DaveM ]
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ipv6.h

@@ -367,6 +367,12 @@ static inline int ipv6_addr_any(const struct in6_addr *a)
 		 a->s6_addr32[2] | a->s6_addr32[3] ) == 0); 
 }
 
+static inline int ipv6_addr_loopback(const struct in6_addr *a)
+{
+	return ((a->s6_addr32[0] | a->s6_addr32[1] |
+		 a->s6_addr32[2] | (a->s6_addr32[3] ^ htonl(1))) == 0);
+}
+
 static inline int ipv6_addr_v4mapped(const struct in6_addr *a)
 {
 	return ((a->s6_addr32[0] | a->s6_addr32[1] |

net/ipv6/ip6_input.c

@@ -102,6 +102,15 @@ int ipv6_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt
 	if (hdr->version != 6)
 		goto err;
 
+	/*
+	 * RFC4291 2.5.3
+	 * A packet received on an interface with a destination address
+	 * of loopback must be dropped.
+	 */
+	if (!(dev->flags & IFF_LOOPBACK) &&
+	    ipv6_addr_loopback(&hdr->daddr))
+		goto err;
+
 	skb->transport_header = skb->network_header + sizeof(*hdr);
 	IP6CB(skb)->nhoff = offsetof(struct ipv6hdr, nexthdr);