[PATCH 4.9 064/103] USB: serial: quatech2: 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>

commit 8c34cb8ddfe808d557b51da983ff10c02793beb2 upstream.

Make sure to detect short control-message transfers when fetching
modem and line state in open and when retrieving registers.

This specifically makes sure that an errno is returned to user space on
errors in TIOCMGET instead of a zero bitmask.

Also drop the unused getdevice function which also lacked appropriate
error handling.

Fixes: f7a33e608d9a ("USB: serial: add quatech2 usb to serial driver")
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/serial/quatech2.c |   24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

--- a/drivers/usb/serial/quatech2.c
+++ b/drivers/usb/serial/quatech2.c
@@ -188,22 +188,22 @@ static inline int qt2_setdevice(struct u
 }
 
 
-static inline int qt2_getdevice(struct usb_device *dev, u8 *data)
-{
-	return usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
-			       QT_SET_GET_DEVICE, 0xc0, 0, 0,
-			       data, 3, QT2_USB_TIMEOUT);
-}
-
 static inline int qt2_getregister(struct usb_device *dev,
 				  u8 uart,
 				  u8 reg,
 				  u8 *data)
 {
-	return usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
-			       QT_SET_GET_REGISTER, 0xc0, reg,
-			       uart, data, sizeof(*data), QT2_USB_TIMEOUT);
+	int ret;
 
+	ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
+			      QT_SET_GET_REGISTER, 0xc0, reg,
+			      uart, data, sizeof(*data), QT2_USB_TIMEOUT);
+	if (ret < sizeof(*data)) {
+		if (ret >= 0)
+			ret = -EIO;
+	}
+
+	return ret;
 }
 
 static inline int qt2_setregister(struct usb_device *dev,
@@ -372,9 +372,11 @@ static int qt2_open(struct tty_struct *t
 				 0xc0, 0,
 				 device_port, data, 2, QT2_USB_TIMEOUT);
 
-	if (status < 0) {
+	if (status < 2) {
 		dev_err(&port->dev, "%s - open port failed %i\n", __func__,
 			status);
+		if (status >= 0)
+			status = -EIO;
 		kfree(data);
 		return status;
 	}