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 <[e-mail]>
Tested-by: Guillermo Jarabo <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

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

drivers/usb/core/message.c

···
 		if (result <= 0 && result != -ETIMEDOUT)
 			continue;
 		if (result > 1 && ((u8 *)buf)[1] != type) {
-			result = -EPROTO;
+			result = -ENODATA;
 			continue;
 		}
 		break;
···
 			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;
 }