linux-kernel - [PATCH 3.2 014/101] USB: serial: mct_u232: fix modem-status error handling

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Message-ID: <lsq.1496331655.764222258@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:40:55 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Johan Hovold" <johan@...nel.org>
Subject: [PATCH 3.2 014/101] USB: serial: mct_u232: fix modem-status error
 handling

3.2.89-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@...nel.org>

commit 36356a669eddb32917fc4b5c2b9b8bf80ede69de upstream.

Make sure to detect short control-message transfers so that errors are
logged when reading the modem status at open.

Note that while this also avoids initialising the modem status using
uninitialised heap data, these bits could not leak to user space as they
are currently not used.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Johan Hovold <johan@...nel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/serial/mct_u232.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/usb/serial/mct_u232.c
+++ b/drivers/usb/serial/mct_u232.c
@@ -385,9 +385,13 @@ static int mct_u232_get_modem_stat(struc
 			MCT_U232_GET_REQUEST_TYPE,
 			0, 0, buf, MCT_U232_GET_MODEM_STAT_SIZE,
 			WDR_TIMEOUT);
-	if (rc < 0) {
+	if (rc < MCT_U232_GET_MODEM_STAT_SIZE) {
 		dev_err(&serial->dev->dev,
 			"Get MODEM STATus failed (error = %d)\n", rc);
+
+		if (rc >= 0)
+			rc = -EIO;
+
 		*msr = 0;
 	} else {
 		*msr = buf[0];