Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757300AbZKRPm6 (ORCPT ); Wed, 18 Nov 2009 10:42:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754822AbZKRPm6 (ORCPT ); Wed, 18 Nov 2009 10:42:58 -0500 Received: from kroah.org ([198.145.64.141]:48997 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753287AbZKRPm5 (ORCPT ); Wed, 18 Nov 2009 10:42:57 -0500 Date: Wed, 18 Nov 2009 07:39:47 -0800 From: Greg KH To: Alan Stern Cc: Jiri Kosina , Russ Dill , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: Use of usb_find_interface in open is racy Message-ID: <20091118153947.GA32440@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2414 Lines: 52 On Wed, Nov 18, 2009 at 10:31:47AM -0500, Alan Stern wrote: > On Wed, 18 Nov 2009, Jiri Kosina wrote: > > > 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. > > I think the proper answer is for usb_find_interface() to use > bus_for_each_dev() instead of driver_for_each_device(). Yeah, I think so, sorry about that I think this is my fault :( I'm travelling all today, could someone make up a patch for this before Thursday if it's an issue? Russ, have you ever hit this problem, or did you just find it by looking at the code? thanks, greg k-h -- 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/