Comments on: Creating a simple ‘hello world’ Netfilter module

By: kasireddi

kasireddi — Mon, 07 Nov 2011 09:41:07 +0000

in $ dmesg
nf_register_hook is unknown….. like this coming

give me solution to overcome this . please .

By: kasireddi

kasireddi — Mon, 07 Nov 2011 08:35:30 +0000

hi PAUL,

i got probelm as NF_IP_PRE_ROUTING not defined.
i resolved as above by changing
nfho.hooknum = NF_IP_PRE_ROUTING;
to
nfho.hooknum = NF_INET_PRE_ROUTING;

but if i do $sudo insmod firewall1.ko i got following

insmod: error inserting ‘firewall1.ko’: -1 Invalid parameters

how to resolve it ?? please help

By: driquet

driquet — Mon, 11 Jul 2011 12:23:32 +0000

To avoid that error, remplace :
nfho.hooknum = NF_IP_PRE_ROUTING;
by
nfho.hooknum = NF_INET_PRE_ROUTING;
.

By: driquet

driquet — Mon, 11 Jul 2011 12:12:40 +0000

I just encounter the same error.
I don’t think this header is build for kernel module.

But, an :
7 #undef __KERNEL__
8 #include
9 #define __KERNEL__
has solved the problem.

Is there any other solution that isn’t that dirty ?

By: dporter

dporter — Thu, 30 Jun 2011 20:05:27 +0000

Paul,
Great post and just what I need.

I’m trying to build this on a later kernel:
Linux ubuntu 2.6.35-22-generic #33-Ubuntu SMP Sun Sep 19 20:34:50 UTC 2010 i686 GNU/Linux

I can get the first program to compile, but the 2nd which introduces netfilter doesnt work for me.
I get this error:
error: ‘NF_IP_PRE_ROUTING’ undeclared (first use in this function)

Looking at the includes, this makes sense because that symbol in netfilter_ipv4.h is hidden behind an
ifndef __KERNEL__
And of course __KERNEL__ is defined so that makes NF_IP_PRE_ROUTING not defined.

Am I doing something wrong? or is my kernel just too different?

Thanks.

By: sunil shah

sunil shah — Mon, 18 Oct 2010 15:05:29 +0000

to get rid of freezing problem change
sk_buff **skb
to
sk_buff *skb

and
socc_buff = * skb to
socc_buff = skb

By: Pankaj Tanwar

Pankaj Tanwar — Sun, 22 Nov 2009 03:38:57 +0000

Thanks Paul It’s just I was trying to find

By: Paul Kiddie

Paul Kiddie — Mon, 02 Nov 2009 12:15:48 +0000

Hi Srudeep,

I was just in the process of writing my next post which deals with that, now live. You can find it at http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/. Just requires some straighforward modifications to the hook_func function — hope it helps,

Paul

By: Paul Kiddie’s Blog : Creating a Netfilter kernel module which filters UDP packets

Mon, 02 Nov 2009 12:12:01 +0000

[...] Last time we created a Netfilter kernel module which simply dropped all packets which gave the structure and functions that need to be implemented for a Netfilter module to work. [...]

By: Srudeep K

Srudeep K — Thu, 29 Oct 2009 18:08:47 +0000

Dear Paul,

I went through your simple kernel module to drop all packets using netfilter hook. I have tried to access the packet headers and data using sk_buff structure. I have analyzed the kernel source code () and found out that there are three fields in the structure to access packet headers (transport_header, network_header and mac_header). I tried to extract source and destination IP addresses using network_header field. Unfortunately, I ended up with segmentation faults. Is there way to access packet data using sk_buff structure (like in kernel 2.4)? If so how can we get a pointer to packet data? How can we extract source and destination addresses? Please help me out….

Best Regards,
Srudeep K