linux-kernel - Re: [PATCH v3 7/9] vfio: Use driver_override to avert binding to compromising drivers

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Date:   Mon, 26 Jun 2017 10:08:55 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Greg KH <greg@...ah.com>
Cc:     kvm@...r.kernel.org, eric.auger@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/9] vfio: Use driver_override to avert binding to
 compromising drivers

On Tue, Jun 20, 2017 at 09:48:31AM -0600, Alex Williamson wrote:
> If a device is bound to a non-vfio, non-whitelisted driver while a
> group is in use, then the integrity of the group is compromised and
> will result in hitting a BUG_ON.  This code tries to avoid this case
> by mangling driver_override to force a no-match for the driver.  The
> driver-core will either follow-up with a DRIVER_NOT_BOUND (preferred)
> or BOUND_DRIVER, at which point we can remove the driver_override
> mangling.

Rather than mangling the driver override string to prevent driver binding,
I wonder if it would make more sense to allow the BUS_NOTIFY_BIND_DRIVER
notifier to fail the device probe?

The driver override strings are, after all, exposed to userspace, and
it strikes me that this kind of mangling is racy - userspace can read
or change the override string at any time.

-- 
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