linux-kernel - Re: [PATCH 0/3] Revert "revocable: Revocable resource management"

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Message-ID: <20260125132433.GQ215800@killaraus>
Date: Sun, 25 Jan 2026 15:24:33 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Danilo Krummrich <dakr@...nel.org>, Johan Hovold <johan@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Tzung-Bi Shih <tzungbi@...nel.org>,
	Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>,
	Linus Walleij <linusw@...nel.org>, Jonathan Corbet <corbet@....net>,
	Shuah Khan <shuah@...nel.org>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Simona Vetter <simona.vetter@...ll.ch>,
	Dan Williams <dan.j.williams@...el.com>,
	Jason Gunthorpe <jgg@...dia.com>, linux-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Revert "revocable: Revocable resource management"

On Sun, Jan 25, 2026 at 01:47:14PM +0100, Greg KH wrote:
> On Sat, Jan 24, 2026 at 08:08:28PM +0100, Danilo Krummrich wrote:
> > On Sat Jan 24, 2026 at 6:05 PM CET, Johan Hovold wrote:
> > > this does not look like the right interface for the chardev unplug issue.
> > 
> > I think it depends, we should do everything to prevent having the issue in the
> > first place, e.g. ensure that we synchronize the unplug properly on device
> > driver unbind.
> > 
> > Sometimes, however, this isn't possible; this is where a revocable mechanism can
> > come in handy to prevent UAF of device resources -- DRM is a good example for
> > this.
> 
> This is not "possible" for almost all real devices so we need something
> like this for almost all classes of devices, DRM just shows the extremes
> involved, v4l2 is also another good example.

Revocable is not needed in V4L2.

> Note, other OSes also have this same problem, look at all the work the
> BSDs are going through at the moment just to get closer to the place
> where we are in Linux today with removable devices and they have hit our
> same problems.
> 
> > But to be fair, I also want to point out that there is a quite significant
> > difference regarding the usefulness of the revocable concept in C compared to in
> > Rust due to language capabilities.
> 
> True, but we do need something.  I took these patches without a real
> user as a base for us to start working off of.  The rust implementation
> has shown that the design-pattern is a good solution for the problem,
> and so I feel we should work with it and try to get this working
> properly.  We've been sitting and talking about it for years now, and
> here is the first real code submission that is getting us closer to fix
> the problem properly.  It might not be perfict, but let's evolve it from
> here for what is found not to work correctly.
> 
> So I don't want to take these reverts, let's try this out, by putting
> this into the driver core now, we have the base to experiment with in a
> "safe" way in lots of different driver subsytems at the same time.  If
> it doesn't work out, worst case we revert it in a release or two because
> it didn't get used.

-- 
Regards,

Laurent Pinchart