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