From: Stephen Hemminger [off-list ref]
   Date: Mon, 23 Jun 2003 12:03:42 -0700

   Could someone who actually receives IGMP packets test this?
   
Don't bother, your patch is buggy.

    	int len = skb->len;
 ...
   +	if (!pskb_may_pull(skb, sizeof(struct igmphdr)))
   +		goto drop;
   +	
   +	ih = skb->h.igmph;
   +	if (ip_compute_csum((void *)ih, len)) 
   +		goto drop;

You're only verifying that "sizeof(struct igmphdr)" is available at
skb->data, then you dereference "len" bytes via the call to
ip_compute_csum().