USB: cdc-wdm: remove from device list on disconnect

Prevents dereferencing an invalid struct usb_interface
pointer.

Always delete entry from device list whether or not the
rest of the device state cleanup is postponed. The device
list uses desc->intf as key, and wdm_open will dereference
this key while searching for a matching device.  A device
should not appear in the list unless probe() has succeeded
and disconnect() has not finished.

Cc: Oliver Neukum <oliver@neukum.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-wdm.c

@@ -309,9 +309,6 @@ static void free_urbs(struct wdm_device *desc)
 
 static void cleanup(struct wdm_device *desc)
 {
-	spin_lock(&wdm_device_list_lock);
-	list_del(&desc->device_list);
-	spin_unlock(&wdm_device_list_lock);
 	kfree(desc->sbuf);
 	kfree(desc->inbuf);
 	kfree(desc->orq);
@@ -782,6 +779,9 @@ static int wdm_create(struct usb_interface *intf, struct usb_endpoint_descriptor
 out:
 	return rv;
 err:
+	spin_lock(&wdm_device_list_lock);
+	list_del(&desc->device_list);
+	spin_unlock(&wdm_device_list_lock);
 	cleanup(desc);
 	return rv;
 }
@@ -907,6 +907,12 @@ static void wdm_disconnect(struct usb_interface *intf)
 	cancel_work_sync(&desc->rxwork);
 	mutex_unlock(&desc->wlock);
 	mutex_unlock(&desc->rlock);
+
+	/* the desc->intf pointer used as list key is now invalid */
+	spin_lock(&wdm_device_list_lock);
+	list_del(&desc->device_list);
+	spin_unlock(&wdm_device_list_lock);
+
 	if (!desc->count)
 		cleanup(desc);
 	else