Subject: Re: Query on usage of multicast as source IPv6 address

From: Brian Haley <[email-masked]>
Date: Mon, 07 Nov 2011 21:11:24 -0500

On 11/07/2011 03:45 PM, Kumar Sanghvi wrote:
> Hi,
> 
> I am trying to understand IPv6 behavior in Linux.
> And I have a doubt related to use of multicast address
> as source address.
> 
> RFC 4291 in Section 2.7 states that:
> "Multicast addresses must not be used as source addresses
>  in IPv6 packets or appear in any Routing header."
> 
> However, what should be the behavior if a host receives a
> packet (probably from a malicious host with pktgen abilities)
> having a multicast address in source address field:
> 1) Should the receiving host discard the packet?

I believe other *nixes silently drop it, can you try this patch?

-Brian

diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 027c7ff..a46c64e 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -111,6 +111,14 @@ int ipv6_rcv(struct sk_buff *skb, struct net_device *dev,
struct packet_type *pt
 	    ipv6_addr_loopback(&hdr->daddr))
 		goto err;

+	/*
+	 * RFC4291 2.7
+	 * Multicast addresses must not be used as source addresses in IPv6
+	 * packets or appear in any Routing header.
+	 */
+	if (ipv6_addr_is_multicast(&hdr->saddr))
+		goto err;
+
 	skb->transport_header = skb->network_header + sizeof(*hdr);
 	IP6CB(skb)->nhoff = offsetof(struct ipv6hdr, nexthdr);