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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH 4.9 27/29] tty: n_gsm: fix proper link termination after failed open
Date:   Mon, 28 Feb 2022 18:23:54 +0100
Message-Id: <20220228172144.391709007@linuxfoundation.org>
In-Reply-To: <20220228172141.744228435@linuxfoundation.org>
References: <20220228172141.744228435@linuxfoundation.org>
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From: daniel.starke@siemens.com <daniel.starke@siemens.com>

commit e3b7468f082d106459e86e8dc6fb9bdd65553433 upstream.

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>
---
 drivers/tty/n_gsm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1506,7 +1506,7 @@ static void gsm_dlci_t1(unsigned long da
 			dlci->mode = DLCI_MODE_ADM;
 			gsm_dlci_open(dlci);
 		} else {
-			gsm_dlci_close(dlci);
+			gsm_dlci_begin_close(dlci); /* prevent half open link */
 		}
 
 		break;