Re: REGISTERING with netfilter hooks - strange behaviour

[KOVACS Krisztian <hidden@sch.bme.hu>]

  Hi,

On cs, júl 26, 2007 at 05:04:37 +0200, Giacomo wrote:
> /* THIS IS THE CALLBACK registered by nf_register_hook() */
> unsigned int
> deliver_process_by_direction(unsigned int hooknum,
> 		struct sk_buff **skb,
> 		const struct net_device *in,
> 		const struct net_device *out,
> 		int (*okfn) (struct sk_buff *))
> {
> 	struct tcphdr* tcph;
> 	struct iphdr *iph;
> 	if(*skb != NULL)
> 	{
> 		iph = (struct iphdr*) skb_network_header(*skb);
> 		if(iph != NULL)
> 		{
> 			if (iph->protocol == IPPROTO_TCP)
> 			{
> 				tcph = (struct tcphdr 
> 				*)skb_transport_header(*skb);
> 				printk("SOURCE: %d - DEST: %d ",
> 				       ntohs(tcph->source), 
> 				       ntohs(tcph->dest) );
> 			}
> 		}
> 	}
> 
> 
> /* THE printk() writes  values  that look like they were uninitialized */
> THe same happens with
> 
> ip_hdr(*skb)
> and tcp_hdr();
> 
> This happens in NF_PRE and NF_IN

  I guess the transport header pointer is not initialized properly when
you're checking for it. I don't exactly know how it behaves after
Arnaldo's changes, but skb->th.* used to be invalid on PREROUTING.

-- 
KOVACS Krisztian