Re: Recalculate checksums in netfilter queue

[Bruno Moreira Guedes <thbmatrix@gmail.com>]

2010/4/20 Justin Yaple <yaplej@gmail.com>:
> Hello,
>
> I am having some trouble figuring out how to re-calculate the tcp/ip
> checksums after pulling a packet into user space with
> libnetfilter_queue.  In a netfilter hook I was able to use this:
> tcph->check = 0;
> tcph->check = tcp_v4_check(tcph, tcplen,
>        iph->saddr,
>        iph->daddr,
>        csum_partial((char *)tcph, tcplen, 0));
>        iph->check = 0;
>        ip_send_check(iph); //ip checksum
>
> In user space these functions tcp_v4_check(), csum_partial() and
> ip_send_check() do not exists.  Are there equivalent functions in user
> space so I can recalculate the ip/tcp checksums before passing the new
> packet back to the kernel with nfq_set_verdict()?
>
> Thanks.
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Hello Justin!

If you solve this problem, I'll be too grateful, because I'm looking
for a solution since the last year in order to do NAT in userspace.
Good luck.
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