Sending a packet through a kernel module

Question

I am trying to create a kernel module that will be able to send out modified packets from ones it receives through netfilter hooking. I'm using a code skeleton provided here. I am creating a raw socket inside the kernel simply using this code:

struct socket *sockptr;
sock_create(PF_INET, SOCK_RAW, IPPROTO_TCP, &sockptr);

The sendpacket function is called by this:

len = sendpacket(sockptr, dev, IPPROTO_TCP, duplicate, ntohs(dupiph->tot_len));

socketptr being the raw socket I created, dev being the net_device in passed to me by the hooking function, and duplicate being a modified copy of the original packet.

The return from the call to dev_queue_xmit indicates that the packet was transmitted successfully but I cannot see the packet on the wire. I have two questions: first, I would like to be able to better debug what is happening so any advice concerning that is much appreciated. Also, I am wondering if I am handling the socket creation properly or if there is some type of configuration I am missing. This is all very new to me so it very well could be that I am missing something silly.

Answer 1

It is unlikely that you need to modify the kernel to accomplish your task. Have you considered using tun or tap interface so you can do all of your work in user space? Here's a tutorial: http://backreference.org/2010/03/26/tuntap-interface-tutorial/