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SubjectRe: [RFC v1 3/3] cap11xx: fix potential user-after-free on module unload
On Tue, Feb 05, 2019 at 10:24:47PM +0100, Jacek Anaszewski wrote:
> Hi Dmitry,
>
> On 2/5/19 9:18 AM, Dmitry Torokhov wrote:
> > Hi Sven,
> >
> > On Mon, Feb 04, 2019 at 05:09:52PM -0500, Sven Van Asbroeck wrote:
> > > The work which is scheduled by led_classdev->brightness_set() is
> > > potentially left pending or running until after the driver module
> > > is unloaded.
> > >
> > > Fix by using resource-controlled version of INIT_WORK().
> >
> > I believe this is wrong way of fixing this. The LED classdev objects are
> > refcounted, and may live beyond the point where we unwibd devm stack,
> > so we are still left with the same use-after-free that we currently
> > have.
>
> Could you please share what LED classdev objects refcounting
> do you have on mind?

My mind was in a state of confusion when I wrote the above ;)

>
> > This is a general issue with LED subsystem as it provides no callback
> > for properly tearing down device structures, but I think in this
> > particular case we can simply switch from set_brightness() to
> > set_brightness_blocking() which will use the work item internal to the
> > LED classdev and that one is being shut down properly.
> >
> > Jacek, does the above sound right?
>
> Yes, since the introduction of brightness_set_blocking op there is no
> need for out-of-led-core workqueues for deferring brightness setting.
> And we do flush_work() in led_classdev_unregister().

OK, great, I'll write up a patch for cap11xx and others if I find them.

Thanks.

--
Dmitry

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