USB: usb_get_string should check the descriptor type

This patch (as1218) fixes a problem with a radio-control joystick used
in the "walkera 4#3" helicopter.  This device responds to the initial
Get-String-Descriptor request for string 0 (which is really the list
of supported languages) by sending its config descriptor!  The
usb_get_string() routine needs to check whether it got the right
type of descriptor.

Oddly enough, this sort of check is already present in
usb_get_descriptor().  The patch changes the error code from -EPROTO
to -ENODATA, because -EPROTO shows up in so many other contexts to
indicate a hardware failure rather than a firmware error.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Guillermo Jarabo <williamjap@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

===================================================================

drivers/usb/core/message.c

@@ -653,7 +653,7 @@ int usb_get_descriptor(struct usb_device *dev, unsigned char type,
 		if (result <= 0 && result != -ETIMEDOUT)
 			continue;
 		if (result > 1 && ((u8 *)buf)[1] != type) {
-			result = -EPROTO;
+			result = -ENODATA;
 			continue;
 		}
 		break;
@@ -696,8 +696,13 @@ static int usb_get_string(struct usb_device *dev, unsigned short langid,
 			USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
 			(USB_DT_STRING << 8) + index, langid, buf, size,
 			USB_CTRL_GET_TIMEOUT);
-		if (!(result == 0 || result == -EPIPE))
-			break;
+		if (result == 0 || result == -EPIPE)
+			continue;
+		if (result > 1 && ((u8 *) buf)[1] != USB_DT_STRING) {
+			result = -ENODATA;
+			continue;
+		}
+		break;
 	}
 	return result;
 }