Re: [PATCH] tty/n_gsm: fix bug in CRC calculation for gsm1 mode

[Alan Cox]

On Sun, 27 Mar 2011 04:05:00 +0400
Mikhail Kshevetskiy <mikhail.kshevetskiy@xxxxxxxxx> wrote:

> Problem description:
>   gsm_queue() calculate a CRC for arrived frames. As a last step of
>   CRC calculation it call
> 
>     gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->received_fcs);
> 
>   This work perfectly for the case of GSM0 mode as gsm->received_fcs
>   contain the last piece of data required to generate final CRC.
> 
>   gsm->received_fcs is not used for GSM1 mode. Thus we put an
>   additional byte to CRC calculation. As result we get a wrong CRC
>   and reject incoming frame.
> 
> Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@xxxxxxxxx>

Acked-by: Alan Cox <alan@xxxxxxxxxxxxxxx>

(This wants cleaning up better as Mikhael also says but this patch is
clear and unlike a big clean up a better base point for a stable fix and
can be reworked further)
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