Hi,
I wrote a kernel module for copy nfs packetsto new packet and send the new packet to network. It works in small packet. But it failed in sending of bigger packets. the program is shown below. I don't know the problem..
/* generic module headers here */
#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/string.h>
#include <linux/vmalloc.h>
#include <linux/nfs.h>
/* scatterlist and page mask required for encrypt */
#include <asm/scatterlist.h>
#include <asm/page.h>
#include <linux/crypto.h>
#include <linux/version.h>
#include <linux/proc_fs.h>
#include <linux/errno.h>
/* network headers here */
#include <linux/byteorder/generic.h>
#include <linux/netdevice.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <net/checksum.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/skbuff.h>
#define IP_PROTO_NFS 105
static
unsigned int
send_hook (unsigned int nfhook, struct sk_buff **skb,
const struct net_device *in, const struct net_device *out,
int (*okfn) (struct sk_buff *))
{
struct sk_buff *skbuff = *skb;
struct sk_buff *skcopy;
struct udphdr *udp_hdr;
int proto, err=0;
int hlen,totlen, troom;
hlen = skbuff ->nh.iph->ihl * 4;
udp_hdr = (struct udphdr *)(skbuff->nh.raw + hlen);
if (udp_hdr -> dest == htons(NFS_PORT) ||
udp_hdr->source == htons(NFS_PORT) &&
skbuff->nh.iph->protocol == IPPROTO_UDP)
{
printk(KERN_ALERT"\n\n Send Hook\n" );
skcopy = skb_copy(skbuff, GFP_ATOMIC);
/*changes in skcopy*/
printk(KERN_INFO"\nsize of packet skbuff%d"
"\nsize of packet skcopy%d",
(skbuff->end - skbuff->head ),
(skcopy->end - skcopy->head ));
skcopy->nh.iph->protocol = IP_PROTO_NFS;
/*sending packet*/
skcopy->nh.iph->check =0;
ip_send_check(skcopy->nh.iph);
ip_finish_output(skcopy);
kfree_skb(skbuff);
return NF_STOLEN;
}
return NF_ACCEPT;
}
;
static
unsigned int
recv_hook (unsigned int nfhook, struct sk_buff **skb,
const struct net_device *in, const struct net_device *out,
int (*okfn) (struct sk_buff *))
{
struct sk_buff *skbuff = *skb;
int proto, err=0;
int hlen,totlen, len;
totlen = ntohs(skbuff->nh.iph->tot_len);
proto = skbuff->nh.iph->protocol;
if(proto == IP_PROTO_NFS) {
printk(KERN_ALERT "\n\nIN RECV_HOOK FUNCTION");
printk(KERN_ALERT"\nproto %d\ntotlen %d",
skbuff->nh.iph->protocol,
ntohs(skbuff->nh.iph->tot_len));
skbuff->nh.iph->protocol = IPPROTO_UDP;
}
return NF_ACCEPT;
}
static struct nf_hook_ops hook_send;
static struct nf_hook_ops hook_recv;
static
int init_module (void)
{
/*encryption hook*/
hook_send.hook = send_hook;
hook_send.hooknum = NF_IP_LOCAL_OUT;
hook_send.pf = PF_INET;
hook_send.priority = NF_IP_PRI_FIRST;
nf_register_hook (&hook_send);
hook_recv.hook = recv_hook;
hook_recv.hooknum = NF_IP_LOCAL_IN;
hook_recv.pf = PF_INET;
hook_recv.priority = NF_IP_PRI_FIRST;
nf_register_hook (&hook_recv);
printk (KERN_INFO "Module successfully loaded.\n");
return 0;
}
static
void cleanup_module(void)
{
nf_unregister_hook(&hook_send);
nf_unregister_hook(&hook_recv);
printk (KERN_ALERT"Module successfully unloaded");
}
MODULE_LICENSE("GPL");
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