How to calculate the TCP checksum

[पारस]

On Tue, Jul 10, 2012 at 11:42 AM, Adel Kodmani <mpcadel at gmail.com> wrote:

> I am writing a kernel module that actually modifies the TCP header(both at
> sending and receiving) and I need to re-calculate the header because of
> that.
> I am capturing the packets using netfilter, so I have access to the whole
> SKB, I am using Linux 2.6.35-22
>
> Looking into the source code of the TCP/IP, I found this function
> void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
> The comment above it says this routing computes the IPv4 TCP checksum
>
> Trying to use this function, I called it passing to it skb->sk and skb
> With no success so far.
>
> So my question is, how do I correctly calculate the TCP checksum? I know
> there's a psudoheader that must be created, and added to the calculation
> but there must be a function in the kernel I can call that already does
> that.
>
>
> Thanks in advance,
> Adel
>
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>
> I think this may be helpful to you
http://www.thegeekstuff.com/2012/05/ip-header-checksum/
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