[PATCH 5.15 166/177] tty: n_gsm: fix wrong command retry handling

Greg Kroah-Hartman
2022-05-04T17:38:33Z

From: Daniel Starke <daniel.starke@siemens.com>

commit d0bcdffcad5a22f202e3bf37190c0dd8c080ea92 upstream.

n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516
The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
the newer 27.010 here. Chapter 5.7.3 states that the valid range for the
maximum number of retransmissions (N2) is from 0 to 255 (both including).
gsm_config() fails to limit this range correctly. Furthermore,
gsm_control_retransmit() handles this number incorrectly by performing
N2 - 1 retransmission attempts. Setting N2 to zero results in more than 255
retransmission attempts.
Fix the range check in gsm_config() and the value handling in
gsm_control_send() and gsm_control_retransmit() to comply with 3GPP 27.010.

Fixes: e1eaea46bb40 ("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/20220414094225.4527-11-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/n_gsm.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1329,7 +1329,6 @@ static void gsm_control_retransmit(struc
spin_lock_irqsave(&gsm->control_lock, flags);
ctrl = gsm->pending_cmd;
if (ctrl) {
- gsm->cretries--;
if (gsm->cretries == 0) {
gsm->pending_cmd = NULL;
ctrl->error = -ETIMEDOUT;
@@ -1338,6 +1337,7 @@ static void gsm_control_retransmit(struc
wake_up(&gsm->event);
return;
}
+ gsm->cretries--;
gsm_control_transmit(gsm, ctrl);
mod_timer(&gsm->t2_timer, jiffies + gsm->t2 * HZ / 100);
}
@@ -1378,7 +1378,7 @@ retry:

/* If DLCI0 is in ADM mode skip retries, it won't respond */
if (gsm->dlci[0]->mode == DLCI_MODE_ADM)
- gsm->cretries = 1;
+ gsm->cretries = 0;
else
gsm->cretries = gsm->n2;

@@ -2278,7 +2278,7 @@ static int gsm_config(struct gsm_mux *gs
/* Check the MRU/MTU range looks sane */
if (c->mru > MAX_MRU || c->mtu > MAX_MTU || c->mru < 8 || c->mtu < 8)
return -EINVAL;
- if (c->n2 < 3)
+ if (c->n2 > 255)
return -EINVAL;
if (c->encapsulation > 1) /* Basic, advanced, no I */
return -EINVAL;