cdc_ether: Ignore bogus union descriptor for RNDIS devices

Some RNDIS devices include a bogus CDC Union descriptor pointing
to non-existing interfaces.  The RNDIS code is already prepared
to handle devices without a CDC Union descriptor by hardwiring
the driver to use interfaces 0 and 1, which is correct for the
devices with the bogus descriptor as well. So we can reuse the
existing workaround.

Cc: Markus Kolb <linux-201011@tower-net.de>
Cc: Iker Salmón San Millán <shaola@esdebian.org>
Cc: Jonathan Nieder <jrnieder@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Cc: 655387@bugs.debian.org
Cc: stable@vger.kernel.org
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/cdc_ether.c

@@ -83,6 +83,7 @@ int usbnet_generic_cdc_bind(struct usbnet *dev, struct usb_interface *intf)
 	struct cdc_state		*info = (void *) &dev->data;
 	int				status;
 	int				rndis;
+	bool				android_rndis_quirk = false;
 	struct usb_driver		*driver = driver_of(intf);
 	struct usb_cdc_mdlm_desc	*desc = NULL;
 	struct usb_cdc_mdlm_detail_desc *detail = NULL;
@@ -195,6 +196,11 @@ int usbnet_generic_cdc_bind(struct usbnet *dev, struct usb_interface *intf)
 					info->control,
 					info->u->bSlaveInterface0,
 					info->data);
+				/* fall back to hard-wiring for RNDIS */
+				if (rndis) {
+					android_rndis_quirk = true;
+					goto next_desc;
+				}
 				goto bad_desc;
 			}
 			if (info->control != intf) {
@@ -271,11 +277,15 @@ int usbnet_generic_cdc_bind(struct usbnet *dev, struct usb_interface *intf)
 	/* Microsoft ActiveSync based and some regular RNDIS devices lack the
 	 * CDC descriptors, so we'll hard-wire the interfaces and not check
 	 * for descriptors.
+	 *
+	 * Some Android RNDIS devices have a CDC Union descriptor pointing
+	 * to non-existing interfaces.  Ignore that and attempt the same
+	 * hard-wired 0 and 1 interfaces.
 	 */
-	if (rndis && !info->u) {
+	if (rndis && (!info->u || android_rndis_quirk)) {
 		info->control = usb_ifnum_to_if(dev->udev, 0);
 		info->data = usb_ifnum_to_if(dev->udev, 1);
-		if (!info->control || !info->data) {
+		if (!info->control || !info->data || info->control != intf) {
 			dev_dbg(&intf->dev,
 				"rndis: master #0/%p slave #1/%p\n",
 				info->control,