linux-kernel - Re: [PATCH] usb: core: Abort deauthorization if unsetting configuration fails

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Date:	Wed, 4 Dec 2013 10:21:07 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Julius Werner <jwerner@...omium.org>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Vincent Palatin <vpalatin@...omium.org>,
	Doug Anderson <dianders@...omium.org>,
	Vivek Gautam <gautam.vivek@...sung.com>
Subject: Re: [PATCH] usb: core: Abort deauthorization if unsetting configuration
 fails

On Tue, 3 Dec 2013, Julius Werner wrote:

> usb_deauthorize_device() tries to unset the configuration of a USB
> device and then unconditionally blows away the configuration descriptors
> with usb_destroy_configuration(). This is bad if the
> usb_set_configuration() call failed before the configuration could be
> correctly unset, since pointers like udev->actconfig can keep pointing
> to the now invalid memory. We have encountered hard to reproduce crashes
> from devices disconnected during suspend due to this, where khubd's
> disconnect handling races with userspace tools that change authorization
> on resume.
> 
> This patch ensures that usb_deauthorize_device() aborts when
> usb_set_configuration() fails, and the underlying status code (such as
> ENODEV) is returned to userspace.

I don't like this approach at all.  It should always be possible to
deauthorize a device, no matter what.

Instead, how about changing usb_set_configuration() so that it will
never fail when the new config is -1?  Except perhaps for -ENODEV 
errors (the device has been disconnected), which 
usb_deauthorize_device() could check for.

Alan Stern

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