Problem with netfilter in a kernel module

Hi,
i was trying to write a simple kernel module which would filter data
based on the tcp destination port. From, what I know, the netfilter
architecture was changed sometime between 2.4 and 2.6 and I'm getting
a lot of conflicting HOWTOs on the net.

Here is the code for my handler function:

unsigned int hook_func(unsigned int hooknum,
struct sk_buff* skb, // should this be
sk_buf** skb ?
const struct net_device *indev,
const struct net_device *outdev,
int (*okfn)(struct sk_buff *)) {

if(!skb) {
return NF_ACCEPT;
}
return drop_by_port(skb,2000);
}

In drop_by_port, I am getting the same address when I try to extract
the transport header using skb_transport_header and the network header
using skb_network_header which points me to believe that something is
wrong with the packet I am getting.

Also, If I change the sk_buf* to sk_buf**, I get *skb (which I pass to
skb_transport_header) to be a Null pointer which crashes the entire
system.

Thanks for any help

--Aashay

On Mar 1, 2:44*am, Aashay Shringarpure <aash...@gmail.com> wrote:
> Hi,
> i was trying to write a simple kernel module which would filter data
> based on the tcp destination port. From, what I know, the netfilter
> architecture was changed sometime between 2.4 and 2.6 and I'm getting
> a lot of conflicting HOWTOs on the net.
>
> Here is the code for my handler function:
>
> unsigned int hook_func(unsigned int hooknum,
> * * * * * * * * * * * * struct sk_buff* skb, * * * * * * * * * * * * *// should this be
> sk_buf** skb ?
> * * * * * * * * * * * * const struct net_device *indev,
> * * * * * * * * * * * * const struct net_device *outdev,
> * * * * * * * * * * * * int (*okfn)(struct sk_buff *)) {
>
> * * * * if(!skb) {
> * * * * * * * * return NF_ACCEPT;
> * * * * }
> * * * * return drop_by_port(skb,2000);
>
> }
>
> In drop_by_port, I am getting the same address when I try to extract
> the transport header using skb_transport_header and the network header
> using skb_network_header which points me to believe that something is
> wrong with the packet I am getting.
>
> Also, If I change the sk_buf* to sk_buf**, I get *skb (which I pass to
> skb_transport_header) to be a Null pointer which crashes the entire
> system.
>
> Thanks for any help
>
> --Aashay

I solved it. I just add the IP header length to its start to get the
transport header's start.