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

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Message-Id: <200911181527.18791.oliver@neukum.org>
Date:	Wed, 18 Nov 2009 15:27:18 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Russ Dill <russ.dill@...il.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: Use of usb_find_interface in open is racy

Am Mittwoch, 18. November 2009 11:41:25 schrieb Jiri Kosina:
> > 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.
> 

Device core code is hard to follow, but I tried.
How about simply covering all of usb_register_dev() with minor_rwsem?

	Regards
		Oliver
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