The hook to netfilter to intercept packet is clear to me.
I don't know how to put the packet back to different tap point than where packet is intercepted. For example, my code hooks to NF_IP_PRE_ROUTING, after processing, I want to bypass routing and deliver the packet to TCP stack which I think the NF_IP_LOCAL_IN is the point I need to inject. This is where I'm stuck now.
Thanks,
Ming
On 4/28/06, Srinivas G. <srinivasg@xxxxxxxxxxxxxxxxxxxxx> wrote:
>I know how to intercept tcp packets at NF_IP_PRE_ROUTING and do what I
have to, but how to put the packet back to >either NF_IP_LOCAL_IN or
NF_IP_LOCAL_OUT in network stack path.
>If you can point me example code that will be great.
Dear Chen,
First of all, you can go through the following link.
http://www.netfilter.org/documentation/HOWTO//netfilter-hacking-HOWTO.ht
ml
Please find some sample code below. I think it may help you.
Thanks and Regards,
Srinivas G
========================================================================
===
/* define netfilter structure here */
static struct nf_hook_ops netfilter_hook;
/* pointer to a buffer */
unsigned char *ptr_packet_buff;
/* function prototype which is called when a packet arrives */
unsigned int netfilter_drv_hook(unsigned int hooknum,
struct sk_buff **skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
printk("One Packet arrvied!\n");
/* alocate the packet buffer */
ptr_packet_buff = (unsigned char *)vmalloc(MAX_PACK_BUFF);
/* the received packet was dropped here itself */
return NF_QUEUE;
}
/* netfilter_init: initialization function */
static int
__init init_netfilter(void)
{
printk("invoked!\n");
/* assign the function pointer */
netfilter_hook.hook = netfilter_drv_hook;
/* assign the protocol family i.e. IPv4 */
netfilter_hook.pf = PF_INET;
/* assign the hook number like NF_IP_LOCAL_IN etc. */
netfilter_hook.hooknum = NF_IP_PRE_ROUTING;
/* assign the hook priority */
netfilter_hook.priority = NF_IP_PRI_FIRST;
/* register the netfilter driver with pointer to structure */
nf_register_hook(&netfilter_hook);
return 0;
}
/* netfilter_exit: cleanup function */
static void
__exit netfilter_exit(void)
{
printk("invoked!\n");
/* unregister the driver */
nf_unregister_hook(&netfilter_hook);
}
/* explicit module definitions */
module_init(init_netfilter);
module_exit(netfilter_exit);
========================================================================
==
