Re: PPTP conntrack for kernel 2.6

[Robbie Dinn <robbie@microbus.com>]

Laurens Blankers wrote:
> Could someone please port the pptp conntrack module to kernel 2.6?

I thought I would have a go at this. It is a bit harder to do
than I thought.

<aside>
At the moment I am stuck trying to fix up function gre_manip_pkt()
in ip_nat_proto_gre.c . I can change the function parameter to
match the function prototype, but I don't know to fix the code
in the body of the function.

I tried looking at functions udp_manip_pkt() and tcp_manip_pkt()
for guidance (in files ip_nat_protocol_{udp|tcp}.c), but I am still
confused.
</aside>

I think I might have spotted something that looks a bit strange,
maybe even a bug? Please bear in mind that I don't understand the
code.

Both udp_manip_pkt() and tcp_manip_pkt() make a call to
skb_ip_make_writable(). It is the second parameter passed to
skb_ip_make_writable() that I am worried about.

In udp_manip_pkt() it is called like this:

      if (!skb_ip_make_writable(pskb, hdroff + sizeof(hdr)))

where hdr is a pointer to a struct udphdr

In tcp_manip_pkt() it is called like this:

      if (!skb_ip_make_writable(pskb, hdroff + hdrsize))

where hdrsize may have a value of sizeof(tcphdr)

I am worried that sizeof(struct udphdr) and sizeof(struct udphdr *)
are different things.

Have I found a bug or am I simply confused?