Help needed!!!!!!!!!!

[swapnil surve <surve.swapnil@gmail.com>]

Hi 
I m  new to kernel developement 
I m trying to send ICMP_ECHOREPLY in responce to ICMP_ECHO from the
kernel itself using netfilter hooks
I m using dev_queue_xmit() to send packets where I dont get a negative
value in return
But for some reason my reply is not received by requester.
please help mehere is my code::
 
#define __KERNEL__
#define MODULE
#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/netdevice.h>
#include<linux/netfilter.h>
#include<linux/netfilter_ipv4.h>
#include<linux/in.h>
//#include<linux/tcp.h>
 
#include <linux/ip.h>
#include <linux/tcp.h>
#include<linux/icmp.h>
#include<linux/if_ether.h>
#include<linux/if_packet.h>
#include<linux/if_arp.h>
#include<net/checksum.h>


 /* This is the structure we shall use to register our function */
 
static struct nf_hook_ops nfho;
static struct nf_hook_ops nfho1;

/* Name of the interface we want to drop packets from */
struct icmphdr *icmp;  
 /* This is the hook function itself */
 
	
in_cksum (addr, len)
     u_short *addr;
     int len;
{
  register int nleft = len;
  register u_short *w = addr;
  register int sum = 0;
  u_short answer = 0;

  /*
   * Our algorithm is simple, using a 32 bit accumulator (sum), we add
   * sequential 16 bit words to it, and at the end, fold back all the
   * carry bits from the top 16 bits into the lower 16 bits.
   */
  while (nleft > 1)
    {
      sum += *w++;
      nleft -= 2;
    }

  /* mop up an odd byte, if necessary */
  if (nleft == 1)
    {
      *(u_char *) (&answer) = *(u_char *) w;
      sum += answer;
    }
  /* add back carry outs from top 16 bits to low 16 bits */
  sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
  sum += (sum >> 16); /* add carry */
  answer = ~sum; /* truncate to 16 bits */
  return (answer);
} 


unsigned int hook_func(unsigned int hooknum,
                       struct sk_buff **skb,
                       const struct net_device *in,
                       const struct net_device *out,
                       int (*okfn)(struct sk_buff *))
{
	unsigned int temp;
	int error;
	struct sk_buff *sb = *skb;
	struct device *ndev= NULL;
	int sum;
	if (sb->nh.iph->protocol == IPPROTO_ICMP) 
	{
/*		printk("\n%d",sb->nh.iph->saddr);
		printk("%d",sb->nh.iph->daddr);
		printk("ICMP PACKET");	        */
		icmp = (struct icmphdr *)(sb->data + sb->nh.iph->ihl * 4);
		//printk("\n checksum before : %x",sb->csum);
		if(icmp->type == ICMP_ECHO)
		{
			
			temp=sb->nh.iph->saddr;
			sb->nh.iph->saddr=sb->nh.iph->daddr;
			sb->nh.iph->daddr=temp;
			sb->pkt_type=PACKET_OUTGOING;
			//icmp_send(sb,ICMP_ECHOREPLY,0,out);
			//ip_send_check(sb->nh.iph);
			//sb->pkt_type=PACKET_OUTGOING;
			icmp->type=ICMP_ECHOREPLY;
			
			icmp->code=0x0;
			icmp->checksum=0;
			
			icmp->checksum=in_cksum((unsigned short
*)icmp,(sb->len-sb->nh.iph->ihl * 4));
			//printk("\nICMP ECHO RECIVED FROM %d",sb->nh.iph->saddr);
			sb->pkt_type=PACKET_OUTGOING;
			
			switch (sb->dev->type) 
			{
				case ARPHRD_PPP:		       
				break;
				case ARPHRD_LOOPBACK:
				case ARPHRD_ETHER:
				{
					unsigned char t_hwaddr[ETH_ALEN];
					//printk("\nchnging mac");
	   				//printk("\n%s",sb->data);
					//sb->len += ETH_HLEN; //sizeof(sb->mac.ethernet);
					memcpy(t_hwaddr, (sb->mac.ethernet->h_dest), ETH_ALEN);
					memcpy((sb->mac.ethernet->h_dest), (sb->mac.ethernet->h_source),ETH_ALEN);
					memcpy((sb->mac.ethernet->h_source), t_hwaddr, ETH_ALEN);
					break;
				}
			}
			
				dev_queue_xmit(sb);
			return NF_STOLEN;
			
		} 
			
	}
return NF_ACCEPT;
}

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

    nf_register_hook(&nfho);

    return 0;
}
	
/* Cleanup routine */
void cleanup_module()
{
    nf_unregister_hook(&nfho);

}