Hi,
I have written a module that changes IP addrs and TCP port values. After
changing these fields, I am able to recalculate the IP checksum within
the module. To recalculate the TCP checksum, I wrote a new function in
tcp_ipv4.c which is very similar to tcp_v4_send_check(). The only
difference is that, my function does not use the sock parameter and gets
the saddr and daddr from sk_buff. I call this function before the
following piece of code in tcp_v4_rcv()
if ((skb->ip_summed != CHECKSUM_UNNECESSARY &&
tcp_v4_checksum_init(skb) < 0))
goto bad_packet;
However I am still getting a bad tcp checksum error. Does anyone know what
I am missing and point me in the right direction.
Thanks,
Rahul.
On Thu, 20 Jan 2005 15:52:34 -0500 (EST)
Rahul Jain <[email protected]> wrote:
> Hi,
>
> I have written a module that changes IP addrs and TCP port values. After
> changing these fields, I am able to recalculate the IP checksum within
> the module. To recalculate the TCP checksum, I wrote a new function in
> tcp_ipv4.c which is very similar to tcp_v4_send_check(). The only
> difference is that, my function does not use the sock parameter and gets
> the saddr and daddr from sk_buff. I call this function before the
> following piece of code in tcp_v4_rcv()
>
> if ((skb->ip_summed != CHECKSUM_UNNECESSARY &&
> tcp_v4_checksum_init(skb) < 0))
> goto bad_packet;
>
> However I am still getting a bad tcp checksum error. Does anyone know what
> I am missing and point me in the right direction.
>
Look at the netfilter code, in fact if you are changing values there may already
be a netfilter module to do what you want, and you could have saved the effort.
--
Stephen Hemminger <[email protected]>