tty: n_gsm: fix wrong DLCI release order

commit deefc58bafb4841df7f0a0d85d89a1c819db9743 upstream.

The current DLCI release order starts with the control channel followed by
the user channels. Reverse this order to keep the control channel open
until all user channels have been released.

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/20220414094225.4527-9-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index ea7283b6037dfaa12d2ffb7c5d5ed3d496ca1674..77bb93262c65b03d674d067fc30462d5a0ce53ff 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2073,8 +2073,8 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
        /* Finish outstanding timers, making sure they are done */
        del_timer_sync(&gsm->t2_timer);
 
-       /* Free up any link layer users */
-       for (i = 0; i < NUM_DLCI; i++)
+       /* Free up any link layer users and finally the control channel */
+       for (i = NUM_DLCI - 1; i >= 0; i--)
                if (gsm->dlci[i])
                        gsm_dlci_release(gsm->dlci[i]);
        mutex_unlock(&gsm->mutex);