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tty: n_gsm: fix frame reception handling 

The frame checksum (FCS) is currently handled in gsm_queue() after
reception of a frame. However, this breaks layering. A workaround with
'received_fcs' was implemented so far.
Furthermore, frames are handled as such even if no end flag was received.
Move FCS calculation from gsm_queue() to gsm0_receive() and gsm1_receive().
Also delay gsm_queue() call there until a full frame was received to fix
both points.

Fixes: e1eaea46bb ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220414094225.4527-6-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Starke 2022-04-14 02:42:11 -07:00 committed by Greg Kroah-Hartman
parent 06d5afd4d6
commit 7a0e4b1733
1 changed files with 30 additions and 23 deletions
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51
drivers/tty/n_gsm.c
View File

@ -219,7 +219,6 @@ struct gsm_mux {
int encoding;
u8 control;
u8 fcs;
u8 received_fcs;
u8 *txframe; /* TX framing buffer */
/* Method for the receiver side */
@ -1794,18 +1793,7 @@ static void gsm_queue(struct gsm_mux *gsm)
u8 cr;
int address;
int i, j, k, address_tmp;
/* We have to sneak a look at the packet body to do the FCS.
A somewhat layering violation in the spec */
if ((gsm->control & ~PF) == UI)
gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf, gsm->len);
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)
@ -1993,19 +1981,25 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
break;
case GSM_DATA: /* Data */
gsm->buf[gsm->count++] = c;
if (gsm->count == gsm->len)
if (gsm->count == gsm->len) {
/* Calculate final FCS for UI frames over all data */
if ((gsm->control & ~PF) != UIH) {
gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf,
gsm->count);
}
gsm->state = GSM_FCS;
}
break;
case GSM_FCS: /* FCS follows the packet */
gsm->received_fcs = c;
gsm_queue(gsm);
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
gsm->state = GSM_SSOF;
break;
case GSM_SSOF:
if (c == GSM0_SOF) {
gsm->state = GSM_SEARCH;
break;
}
if (c == GSM0_SOF)
gsm_queue(gsm);
else
gsm->bad_size++;
break;
default:
pr_debug("%s: unhandled state: %d\n", __func__, gsm->state);
@ -2024,11 +2018,24 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
{
if (c == GSM1_SOF) {
/* EOF is only valid in frame if we have got to the data state
and received at least one byte (the FCS) */
if (gsm->state == GSM_DATA && gsm->count) {
/* Extract the FCS */
/* EOF is only valid in frame if we have got to the data state */
if (gsm->state == GSM_DATA) {
if (gsm->count < 1) {
/* Missing FSC */
gsm->malformed++;
gsm->state = GSM_START;
return;
}
/* Remove the FCS from data */
gsm->count--;
if ((gsm->control & ~PF) != UIH) {
/* Calculate final FCS for UI frames over all
* data but FCS
*/
gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf,
gsm->count);
}
/* Add the FCS itself to test against GOOD_FCS */
gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->buf[gsm->count]);
gsm->len = gsm->count;
gsm_queue(gsm);