Hooking on L4 Level with process information

Hi,

I want to hook tcp/udp packets on L4 Layer and based on process
information , content want to deny or allow packets.

Netfilter provides pre/post Routing hooks but not sure that will be
right place so thought of asking whether my approach is right.
Also how i can get process information whether this packet is send by
this process.

Thoughts /source code reference would be appreciated.

Regards,
Ravish