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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 5.15 161/177] tty: n_gsm: fix malformed counter for out of frame data
Date:   Wed,  4 May 2022 18:45:54 +0200
Message-Id: <20220504153107.896678169@linuxfoundation.org>
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From: Daniel Starke <daniel.starke@siemens.com>

commit a24b4b2f660b7ddf3f484b37600bba382cb28a9d upstream.

The gsm_mux field 'malformed' represents the number of malformed frames
received. However, gsm1_receive() also increases this counter for any out
of frame byte.
Fix this by ignoring out of frame data for the malformed counter.

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/20220414094225.4527-7-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/n_gsm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1976,7 +1976,8 @@ static void gsm1_receive(struct gsm_mux
 		}
 		/* Any partial frame was a runt so go back to start */
 		if (gsm->state != GSM_START) {
-			gsm->malformed++;
+			if (gsm->state != GSM_SEARCH)
+				gsm->malformed++;
 			gsm->state = GSM_START;
 		}
 		/* A SOF in GSM_START means we are still reading idling or