우분투에서 netfilter를 이용한 간단한 패킷 뷰어를 만들려고 하는데요...

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/netfilter.h>
#include <linux/proc_fs.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/netdevice.h>
#include <asm/uaccess.h>
 
 
static struct proc_dir_entry *packet_dir=NULL;
static struct proc_dir_entry *packets=NULL;
 
static char proc_buf[100];
static int proc_buf_size=0;
 
/*static void print_str(char *str) {
  struct tty_struct *my_tty;
  my_tty = current->signal->tty;
  if(my_tty != NULL) 
    ((my_tty->driver)->write(my_tty,str,strlen(str)));
}*/
static int readproc(char * page, char **start, off_t off, int count, int *eof, void *data){
  memcpy(page, proc_buf, proc_buf_size);
  return proc_buf_size;	
}
static int writeproc(struct file *file, const char *buffer, unsigned long count, void *data) {
	copy_from_user(proc_buf, buffer, count);
	return count;
}
unsigned int hook_simple(unsigned int hook_no, struct sk_buff **pskb, const struct net_device *dev_in, const struct net_device *dev_out, int (*handler)(struct sk_buff *)) {
	struct iphdr *iph = ip_hdr(*pskb);
	struct tcphdr *th = tcp_hdr(*pskb);
 
	//if(iph->protocol == 6)  printk(KERN_ERR "TCP\n");
	char *data = NULL;
	int ctr=0;
	unsigned int length=0;
	unsigned long saddr=0, daddr=0;
	unsigned short sport=0, dport=0;
 
	//length = ((*pskb)->len) - (iph->ihl*4) - (th->doff*4);  // data size
	//length = ((*pskb)->data_len);
	//data = kmalloc(length, GFP_KERNEL);
	saddr = iph->saddr;
	proc_buf_size += sprintf(proc_buf, "%lu.%lu.%lu.%lu\n", 
	(saddr&0xFF000000)>>24, (saddr&0x00FF0000)>>16,
	(saddr&0x0000FF00)>>8  , (saddr&0x000000FF)); 
	daddr = iph->daddr;
	sport = th->source;
	dport = th->dest;
	/*memset(data, 0, length);
	memcpy(data, (unsigned char *)th + th
	unsigned int length=0;->doff*4, length);
	saddr = ntohl(iph->saddr);
	daddr = ntohl(iph->daddr);
	sport = th->source;
	dport = th->dest;*/
 
	/*printk(KERN_ALERT "%lu.%lu.%lu.%lu:%5u --> %lu.%lu.%lu.%lu:%5u  \n", 
	(saddr&0xFF000000)>>24, (saddr&0x00FF0000)>>16,
	(saddr&0x0000FF00)>>8  , (saddr&0x000000FF), sport,
	(daddr&0xFF000000)>>24, (daddr&0x00FF0000)>>16,
	(daddr&0x0000FF00)>>8  , (daddr&0x000000FF), dport);*/
 
	//for(ctr=0; ctr<length; ctr++);  //printk("%02x\n", *(data+ctr));
	kfree(data);
	return NF_ACCEPT;
}
 
static struct nf_hook_ops nfilter = {
	.hook = hook_simple,
	.pf = PF_INET,
	.hooknum = NF_IP_LOCAL_IN,
	.priority = NF_IP_PRI_FIRST
};
 
int nfilter_init(void) {
	int ret;
	packet_dir = proc_mkdir("packets", NULL);
	packets = create_proc_entry("packet", 0, packet_dir);
	packets->read_proc = readproc;
	packets->write_proc = writeproc;
	ret = nf_register_hook(&nfilter);
	if (ret < 0){
		printk(KERN_ALERT "netfilter init error!. \n");	
		return ret;
	}else {
		printk(KERN_ALERT "netfilter start. \n");
		return 0;
	}
}
 
void nfilter_exit(void) {
	nf_unregister_hook(&nfilter);
	remove_proc_entry("packet", packet_dir);
	remove_proc_entry("packets", 0);
	printk(KERN_ALERT "netfilter finish. \n");
}
 
module_init(nfilter_init);
module_exit(nfilter_exit);