From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Westphal <fw@strlen.de>
Subject: Re: Netfilter hook doesn't see all packets
Date: Thu, 21 Nov 2019 21:36:24 +0100
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To: Psyspy rambo <psyspy2020@gmail.com>
Cc: Gordon Fisher <gordfisherman@gmail.com>, netfilter@vger.kernel.org

Psyspy rambo <psyspy2020@gmail.com> wrote:
> > >      udp_header = (struct udphdr *)skb_transport_header(skb);
> > >      sip = (unsigned int)ntohl(ip_header->saddr);
> > >      dip = (unsigned int)ntohl(ip_header->daddr);

This doesn't work reliably in netfilter hooks.

See skb_header_pointer() usage in other nf modules.