2.6.30内核Netfilter的简单例子、六（filterPort）

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netdevice.h>

MODULE_LICENSE("GPL");

/* This is the structure we shall use to register our function */
static struct nf_hook_ops nfho;

/* IP address we want to drop packets from, in NB order */
static unsigned char *deny_port = "\x00\x50";   /* port 80 */


/* This is the hook function itself */
unsigned int hook_func(unsigned int hooknum,
                           struct sk_buff *skb, //2.6.18的版本里为**skb
                           const struct net_device *in,
                           const struct net_device *out,
                           int (*okfn)(struct sk_buff *))
{
  struct sk_buff *sb = skb;
  struct iphdr *iph;
  struct tcphdr *tcph;

  if(!sb) return NF_ACCEPT;
  iph = ip_hdr(sb);
  if(!iph) return NF_ACCEPT;

  /*Make sure this is a TCP packet first*/
  if(iph->protocol != IPPROTO_TCP)
  {
    return NF_ACCEPT;
  }
  tcph = (struct tcphdr *)(sb->data + iph->ihl * 4);
  //tcph = tcp_hdr(sb);
  //pr_warning("%d.%d.%d.%d:%u\t%d.%d.%d.%d:%u\n",NIPQUAD(iph->saddr),ntohs(tcph->source),NIPQUAD(iph->daddr),ntohs(tcph->dest));
  if(tcph->dest == *(__be16 *)deny_port)
  {
    pr_warning("Dropped packet to prot %d\n",ntohs(tcph->dest) );
    return NF_DROP;
  }

  return NF_ACCEPT;

}
/* Initialisation routine */
int init_module()
{
  /* Fill in our hook structure */
  nfho.hook     = hook_func;         /* Handler function */
  nfho.hooknum  = NF_INET_PRE_ROUTING; /* First hook for IPv4 */
  nfho.pf       = PF_INET;
  nfho.priority = NF_IP_PRI_FIRST;   /* Make our function first */

  nf_register_hook(&nfho);

  pr_info("filterPort install into kernel!\n");
  return 0;
}
/* Cleanup routine */
void cleanup_module()
{
  nf_unregister_hook(&nfho);
  pr_info("filterPort removed from kernel!\n");
}

2、Makefile：

obj-m +=filterPort.o
all:
  make -C /usr/src/linux/ SUBDIRS=$(PWD) modules
clean:
  make -C /usr/src/linux M=$(PWD) clean
install:
  /sbin/insmod filterPort.ko
remove:
  /sbin/rmmod filterPort