Re: How to calculate the TCP checksum

[Adel Kodmani <mpcadel@xxxxxxxxx>]

On Mon, Jul 16, 2012 at 1:30 PM, पारस <beparas@xxxxxxxxx> wrote:

On Tue, Jul 10, 2012 at 11:42 AM, Adel Kodmani <mpcadel@xxxxxxxxx> 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/

Nope, what I need to calculate is the TCP checksum, not the IP checksum

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