linux-kernel - Re: Use of usb_find_interface in open is racy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 18 Nov 2009 11:41:25 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Russ Dill <russ.dill@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: Use of usb_find_interface in open is racy


[ 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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/