tty/n_gsm: fix bug in CRC calculation for gsm1 mode
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>
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 47f8cdb..74273e6 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1658,8 +1658,12 @@
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)