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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>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 395/545] tty: n_gsm: fix DM command
Date:   Fri, 19 Aug 2022 17:42:45 +0200
Message-Id: <20220819153847.089036026@linuxfoundation.org>
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From: Daniel Starke <daniel.starke@siemens.com>

[ Upstream commit 18a948c7d90995d127785e308fa7b701df4c499f ]

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 5.3.3 defines the DM response. There exists
no DM command. However, the current implementation incorrectly sends DM as
command in case of unexpected UIH frames in gsm_queue().
Correct this behavior by always sending DM as response.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220707113223.3685-2-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 3f100f7abdb7..a6c0a1b76ddb 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1938,7 +1938,7 @@ static void gsm_queue(struct gsm_mux *gsm)
 			goto invalid;
 #endif
 		if (dlci == NULL || dlci->state != DLCI_OPEN) {
-			gsm_command(gsm, address, DM|PF);
+			gsm_response(gsm, address, DM|PF);
 			return;
 		}
 		dlci->data(dlci, gsm->buf, gsm->len);
-- 
2.35.1