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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Fri, 26 Apr 2024 11:18:33 +0200
Message-ID: <CAJZ5v0hNpZEiaV-wuKfZuwZkFr_5k_oaw2RNHYYa3iQCsu2cMA@mail.gmail.com>
Subject: Re: [PATCH v1 3/3] thermal/debugfs: Prevent use-after-free from
 occurring after cdev removal
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linux PM <linux-pm@vger.kernel.org>, 
	LKML <linux-kernel@vger.kernel.org>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Daniel Lezcano <daniel.lezcano@linaro.org>
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On Fri, Apr 26, 2024 at 12:05=E2=80=AFAM Lukasz Luba <lukasz.luba@arm.com> =
wrote:
>
>
>
> On 4/25/24 14:57, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Since thermal_debug_cdev_remove() does not run under cdev->lock, it can
> > run in parallel with thermal_debug_cdev_state_update() and it may free
> > the struct thermal_debugfs object used by the latter after it has been
> > checked against NULL.
> >
> > If that happens, thermal_debug_cdev_state_update() will access memory
> > that has been freed already causing the kernel to crash.
> >
> > Address this by using cdev->lock in thermal_debug_cdev_remove() around
> > the cdev->debugfs value check (in case the same cdev is removed at the
> > same time in two differet threads) and its reset to NULL.
>
> s/differet/different/
>
> >
> > Fixes: 755113d76786 ("thermal/debugfs: Add thermal cooling device debug=
fs information")
> > Cc :6.8+ <stable@vger.kernel.org> # 6.8+
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >   drivers/thermal/thermal_debugfs.c |   10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > Index: linux-pm/drivers/thermal/thermal_debugfs.c
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > --- linux-pm.orig/drivers/thermal/thermal_debugfs.c
> > +++ linux-pm/drivers/thermal/thermal_debugfs.c
> > @@ -503,15 +503,21 @@ void thermal_debug_cdev_add(struct therm
> >    */
> >   void thermal_debug_cdev_remove(struct thermal_cooling_device *cdev)
> >   {
> > -     struct thermal_debugfs *thermal_dbg =3D cdev->debugfs;
> > +     struct thermal_debugfs *thermal_dbg;
> >
> > +     mutex_lock(&cdev->lock);
> > +
> > +     thermal_dbg =3D cdev->debugfs;
> >       if (!thermal_dbg)
>
> mutex_unlock(&cdev->lock) missing here

Good catch, thanks!

Ho-hum, I'm not sure why I haven't added it here ...

I'll send a v2 of this patch shortly.

> >               return;
> >
> > +     cdev->debugfs =3D NULL;
> > +
> > +     mutex_unlock(&cdev->lock);
> > +
> >       mutex_lock(&thermal_dbg->lock);
> >
> >       thermal_debugfs_cdev_clear(&thermal_dbg->cdev_dbg);
> > -     cdev->debugfs =3D NULL;
> >
> >       mutex_unlock(&thermal_dbg->lock);
> >
> >
> >
> >
> >
>