usbfs: Allow printer class 'get_device_id' without needing to claim the intf

For certain (HP) printers the printer device_id does not only contain a
static part identifying the printer, but it also contains a dynamic part
giving printer status, ink level, etc.

To get to this info various userspace utilities need to be able to make a
printer class 'get_device_id' request without first claiming the interface
(as that is in use for the actual printer driver).

Since the printer class 'get_device_id' request does not change interface
settings in anyway, allowing this without claiming the interface should not
cause any issues.

CC: Sanjay Kumar <sanjay.kumar14@hp.com>
CC: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/devio.c

@@ -725,15 +725,15 @@ static int check_ctrlrecip(struct dev_state *ps, unsigned int requesttype,
 
 	/*
 	 * check for the special corner case 'get_device_id' in the printer
-	 * class specification, where wIndex is (interface << 8 | altsetting)
-	 * instead of just interface
+	 * class specification, which we always want to allow as it is used
+	 * to query things like ink level, etc.
 	 */
 	if (requesttype == 0xa1 && request == 0) {
 		alt_setting = usb_find_alt_setting(ps->dev->actconfig,
 						   index >> 8, index & 0xff);
 		if (alt_setting
 		 && alt_setting->desc.bInterfaceClass == USB_CLASS_PRINTER)
-			index >>= 8;
+			return 0;
 	}
 
 	index &= 0xff;