Re: changing packet length?

[Todd Underwood <todd@docforge.org>]

Harald, all,

On Fri, May 06, 2005 at 01:14:10PM +0200, Harald Welte wrote:
> On Tue, May 03, 2005 at 05:34:06PM -0400, BJ Premore wrote:
> > So my hopefully simple question is, can packet sizes be
> > changed and then reinjected using ipq_set_verdict?  
> 
> Of course. you just reinject the packet with a different data_len.
> 

this seems not to work.  given the code that was posted, the trivial
case of this fails:  adding 4 bytes of option-1 to the tcp header,
changing the checksum and changing the size.

the data gets corrupted.  

is there some simple bug that i'm not seeing the in the header/data
handling code that was posted.  running tcpdump, i see the same errors
that bj was reporting.

scouring the web i can find *no* examples of anyone changing the size
of the header or the data in ipq userspace processes.  without being
able to do that, interesting things (like a userspace md5 signing
implementation) are obviously not possible.

harald:  did you mean something by 'reinject' other than
ipq_set_verdict, with new data?

todd