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From:   daniel.starke@siemens.com
To:     linux-serial@vger.kernel.org, gregkh@linuxfoundation.org,
        jirislaby@kernel.org
Cc:     linux-kernel@vger.kernel.org,
        Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH 1/1] tty: n_gsm: fix proper link termination after failed open
Date:   Thu, 17 Feb 2022 00:05:51 -0800
Message-Id: <20220217080555.5387-3-daniel.starke@siemens.com>
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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>
---
 drivers/tty/n_gsm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 0b1808e3a912..52224a3494a0 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1514,7 +1514,7 @@ 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;
-- 
2.25.1