tty: n_gsm: fix proper link termination after failed open

Trying to open a DLCI by sending a SABM frame may fail with a timeout.
The link is closed on the initiator side without informing the responder
about this event. The responder assumes the link is open after sending a
UA frame to answer the SABM frame. The link gets stuck in a half open
state.

This patch fixes this by initiating the proper link termination procedure
after link setup timeout instead of silently closing it down.

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/20220218073123.2121-3-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 db41b9e5d35e05fd994fd934dc796617488fbb13..53fa1cec49bd4f2bae99a62e1016a96a9d71a801 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1518,7 +1518,7 @@ static void gsm_dlci_t1(struct timer_list *t)
                        dlci->mode = DLCI_MODE_ADM;
                        gsm_dlci_open(dlci);
                } else {
-                       gsm_dlci_close(dlci);
+                       gsm_dlci_begin_close(dlci); /* prevent half open link */
                }
 
                break;