Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756204AbZKRKlW (ORCPT ); Wed, 18 Nov 2009 05:41:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754351AbZKRKlV (ORCPT ); Wed, 18 Nov 2009 05:41:21 -0500 Received: from cantor.suse.de ([195.135.220.2]:51052 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753159AbZKRKlU (ORCPT ); Wed, 18 Nov 2009 05:41:20 -0500 Date: Wed, 18 Nov 2009 11:41:25 +0100 (CET) From: Jiri Kosina X-X-Sender: jikos@twin.jikos.cz To: Russ Dill Cc: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: Use of usb_find_interface in open is racy In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LRH 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1884 Lines: 42 [ linux-usb should be CCed here at least ] On Tue, 17 Nov 2009, Russ Dill wrote: > Many usb drivers that create character devices use "struct > usb_class_driver", a set of fops, and a usb_find_interface in their > open call. A prime example is drivers/usb/usb-skeleton.c. A race > occurs when userspace receives a hotplug event for the addition for > the interface and then opens the associated device file before the > device is added to the driver's klist_devices. > > The usb core senses a new usb device (usb_new_device) and calls > device_add. This eventually gets down to really_probe and the > usb-skeleton probe function, skel_probe. skel_probe calls > usb_register_dev() which registers the associated character device for > skel_class. The hotplug events for the class device get emitted. > > User space receives the hotplug event for the class device, makes the > device node and notifies another program that opens the device node. > The program opens the device node which calls into usb_open and then > skel_open. skel_open calls usb_find_interface. usb_find_interfaces > searches the klist_devices of skel_driver, finds no device associated > with the minor number and returns NULL. skel_open returns -ENODEV. > > Control returns to really_probe and really_probe calls driver_bound > which adds the device to the list of devices associated with > skel_driver (klist_devices). > > I'm not sure what the right way to solve this is. A call to > wait_for_device_probe() in the skel_open call before calling > usb_find_interface fixes the problem, but it is a rather large hammer. -- Jiri Kosina SUSE Labs, Novell Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/