CODEWITHSUNDEEP
clinux-kernelnetwork-programmingkernellinux-device-driver
Milad Khajavi
Milad Khajavi

Reputation: 2859

How to push skb in specific point of Linux network stack?

I want to push skb to prerouting point of Linux network stack. Is there any way to do this? I used dev_queue_xmit() and netif_rx() functions, but I don't think they can push skb in prerouting point of Linux network stack.

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Upvotes: 9

Views: 1980

Answers (3)

Jefferson
Jefferson

Reputation: 529

I think the function you are looking for is ip_queue_xmit(), which is where IPV4 implementation starts checking tables, filters, etc.

Upvotes: 0

abligh
abligh

Reputation: 25129

I'm not entirely clear where this skb originates from. In userland, there are two ways to do this. One is to use a tun device (and simply write the packet in). The other is to use libpcap (which has the little known feature of sending raw packets hidden amongst all the receive stuff).

You say you want to do this by registering an ioctl (presumably meaning adding your own ioctl) then calling the ioctl from user space. It isn't immediately obvious why you would want to do that when you can already achieve this without modifying the kernel. However, if you did want to do this, what I'd do is follow the path the tun driver uses, and do the equivalent of write()-ing to the tun device in your new ioctl. That might mean having a tun-like interface hanging around to act as the source for the packets. I suspect packets in the system need a source interface of sorts.

Upvotes: 2

Clarus
Clarus

Reputation: 2338

I suspect you want libpcap or libnetfilter_queue hereafter collectively referred to as userland queuing. Userland queuing will route all packets matching some rule (you define) to your userland application. The dev_queue_* and netif_* functions apply to kernel level routing and are not relevant to userland applications.

Userland queuing has performance implications and depending on the library you use you will have to use a specific method of re-injecting your packet back into the netfilter queues.

Upvotes: 1

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