Firewall

Hello

I'm trying to write simple firewall. But I have problem with tcp filtering.

I'm using 2.6.27 kernel.

Here is my code which supposed to block everything except www.

#define __KERNEL__
#define MODULE

#include <linux/kernel.h> /* Kernel */
#include <linux/module.h> /* Module */
#include <linux/netfilter.h> /* Netfilter */
#include <linux/netfilter_ipv4.h> /* Netfiletr for IPv4 */
#include <linux/skbuff.h> /* Socket Kernel Buffers */
#include <linux/ip.h> /* IP Header*/
#include <linux/tcp.h>

static struct nf_hook_ops netfilter_ops;

/* Adres odblokowany: 212.77.100.101 (wp.pl) */ static unsigned char *ip_address = "\xD4\x4D\x64\x65"; unsigned char *port = "\x00\x50";

unsigned int main_hook(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;
   tcpH=(struct tcphdr *) skb_transport_header(skb);
   //tcpH=tcp_hdr(skb)dr(skb); no difference
   if(tcpH->dest==*(unsigned short*) port)
   return NF_ACCEPT;
   else
   return NF_DROP;

   /*struct iphdr * ipHead;
   ipHead = ip_hdr( skb );

if (ipHead == NULL)

       return NF_DROP;

if (ipHead->saddr == *(unsigned int*)ip_address)

       return NF_ACCEPT;

else
return NF_DROP;*/

//return NF_ACCEPT;
}

int init_module()
{
netfilter_ops.hook = main_hook;
netfilter_ops.hooknum = NF_INET_PRE_ROUTING;
netfilter_ops.pf = PF_INET;
netfilter_ops.priority = NF_IP_PRI_FIRST;

   nf_register_hook(&netfilter_ops);

return 0;
}

void cleanup_module() {
nf_unregister_hook(&netfilter_ops);
}