[PATCH 4.9 040/104] USB: serial: mos7840: fix control-message error handling

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Johan Hovold <johan@xxxxxxxxxx>


[ Upstream commit cd8db057e93ddaacbec025b567490555d2bca280 ]

Make sure to detect short transfers when reading a device register.

The modem-status handling had sufficient error checks in place, but move
handling of short transfers into the register accessor function itself
for consistency.

Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/usb/serial/mos7840.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

--- a/drivers/usb/serial/mos7840.c
+++ b/drivers/usb/serial/mos7840.c
@@ -285,9 +285,15 @@ static int mos7840_get_reg_sync(struct u
 	ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), MCS_RDREQ,
 			      MCS_RD_RTYPE, 0, reg, buf, VENDOR_READ_LENGTH,
 			      MOS_WDR_TIMEOUT);
+	if (ret < VENDOR_READ_LENGTH) {
+		if (ret >= 0)
+			ret = -EIO;
+		goto out;
+	}
+
 	*val = buf[0];
 	dev_dbg(&port->dev, "%s offset is %x, return val %x\n", __func__, reg, *val);
-
+out:
 	kfree(buf);
 	return ret;
 }
@@ -353,8 +359,13 @@ static int mos7840_get_uart_reg(struct u
 	ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), MCS_RDREQ,
 			      MCS_RD_RTYPE, Wval, reg, buf, VENDOR_READ_LENGTH,
 			      MOS_WDR_TIMEOUT);
+	if (ret < VENDOR_READ_LENGTH) {
+		if (ret >= 0)
+			ret = -EIO;
+		goto out;
+	}
 	*val = buf[0];
-
+out:
 	kfree(buf);
 	return ret;
 }
@@ -1490,10 +1501,10 @@ static int mos7840_tiocmget(struct tty_s
 		return -ENODEV;
 
 	status = mos7840_get_uart_reg(port, MODEM_STATUS_REGISTER, &msr);
-	if (status != 1)
+	if (status < 0)
 		return -EIO;
 	status = mos7840_get_uart_reg(port, MODEM_CONTROL_REGISTER, &mcr);
-	if (status != 1)
+	if (status < 0)
 		return -EIO;
 	result = ((mcr & MCR_DTR) ? TIOCM_DTR : 0)
 	    | ((mcr & MCR_RTS) ? TIOCM_RTS : 0)