netdev - Help required in a part of transport layer

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Message-ID: <CA+bQXLQAGhW9QwLmofBNTBfq3fuKTeEDOc9WJWztLFYgyJfHfQ@mail.gmail.com>
Date:   Fri, 12 Jul 2019 11:51:35 +0530
From:   Rakesh Beck <beckrakesh@...il.com>
To:     netdev@...r.kernel.org
Subject: Help required in a part of transport layer

Hi,
I am looking for some help.

I am trying to intercept packet using netfilter hooks
(NF_IP_LOCAL_OUT) and using source port and destination port from
SK_BUFF, to figure out which processes are using it but I am unable to
do so.

I am only concerned about packets which are sent and received locally.
Therefore, I looked into __udp4_lib_rcv (net/ipv4/udp.c) to see how
packet is assigned to socket and from socket to infer which process is
using it (For receiver). I called udp4_lib_lookup_skb from netfilter
hook but it causes kernel null pointer deference.
For sender, I was thinking to add sending  process pid to sk_buff's secmark.

Is this the correct way to do or is there any other way? kindly point
me to resources which will help me achieve my goal.

Thanks,
Rakesh