how ipfw firewall is implemented in the kernel

[Max Laier]

On Wednesday 14 January 2009 18:32:07 Biks N wrote:
> Hi,
>
> Can anyone please help me understand how the IPFW firewall is
> implemented in the kernel.
>
> I have created new ACTIONS in ipfw. I have already implemented in the
> userland.
>
> Now i need to check the IPFW rule list (in ip_input.c and in
> ip_output.c) and call a custom routine if there is a match to those
> rules.
>
> I would really appreciate if anyone could point me to right
> direction/reference.

ipfw is hooked into the pfil(9) hook points in ip_{in,out}put() (look for 
calls to pfil_run_hooks() in the respective files).

From there the call path goes on to the ipfw_check_* functions defined in 
netinet/ip_fw_pfil.c

Finally ipfw_chk() in netinet/ip_fw2.c where the ruleset is processed and 
where you should add your required processing.

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