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tty/n_gsm: fix bug in CRC calculation for gsm1 mode

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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@gmail.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Mikhail Kshevetskiy 2011-03-27 04:05:00 +04:00 committed by Greg Kroah-Hartman
parent 5680e94148
commit 9db4e4381a
1 changed files with 6 additions and 2 deletions
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8
drivers/tty/n_gsm.c
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@ -1658,8 +1658,12 @@ static void gsm_queue(struct gsm_mux *gsm)
if ((gsm->control & ~PF) == UI)
gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf, gsm->len);
/* generate final CRC with received FCS */
gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->received_fcs);
if (gsm->encoding == 0){
/* WARNING: gsm->received_fcs is used for gsm->encoding = 0 only.
In this case it contain the last piece of data
required to generate final CRC */
gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->received_fcs);
}
if (gsm->fcs != GOOD_FCS) {
gsm->bad_fcs++;
if (debug & 4)