linux-kernel - Re: [PATCH -next] thermal/drivers/thermal_hwmon: Fix a kernel NULL pointer dereference

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Message-ID: <CAJZ5v0g=2L1s=uNKoo+-KAV_rU=-XetrLhi50HLVGTTqiKefng@mail.gmail.com>
Date:   Wed, 29 Mar 2023 14:01:06 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Zhang, Rui" <rui.zhang@...el.com>
Cc:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] thermal/drivers/thermal_hwmon: Fix a kernel NULL
 pointer dereference

On Wed, Mar 29, 2023 at 1:24 PM Zhang, Rui <rui.zhang@...el.com> wrote:
>
> On Wed, 2023-03-29 at 11:57 +0200, Daniel Lezcano wrote:
> > On 29/03/2023 11:00, Zhang Rui wrote:
> > > When the hwmon device node of a thermal zone device is not found,
> > > using hwmon->device causes a kernel NULL pointer dereference.
> > >
> > > Reported-by: Preble Adam C <adam.c.preble@...el.com>
> > > Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> > > ---
> > > Fixes: dec07d399cc8 ("thermal: Don't use 'device' internal thermal
> > > zone structure field")
> > > dec07d399cc8 is a commit in the linux-next branch of linux-pm repo.
> > > I'm not sure if the Fix tag applies to such commit or not.
> >
> > Actually it reverts the work done to encapsulate the thermal zone
> > device
> > structure.
> >
> > > ---
> > >   drivers/thermal/thermal_hwmon.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/thermal/thermal_hwmon.c
> > > b/drivers/thermal/thermal_hwmon.c
> > > index c59db17dddd6..261743f461be 100644
> > > --- a/drivers/thermal/thermal_hwmon.c
> > > +++ b/drivers/thermal/thermal_hwmon.c
> > > @@ -229,7 +229,7 @@ void thermal_remove_hwmon_sysfs(struct
> > > thermal_zone_device *tz)
> > >     hwmon = thermal_hwmon_lookup_by_type(tz);
> > >     if (unlikely(!hwmon)) {
> > >             /* Should never happen... */
> > > -           dev_dbg(hwmon->device, "hwmon device lookup
> > > failed!\n");
> > > +           dev_dbg(&tz->device, "hwmon device lookup failed!\n");
> >
> > As it 'Should never happen', I would replace that by:
> >
> >       if (WARN_ON(!hwmon))
> >               /* Should never happen... */
> >               return;
>
> Actually, the comment is wrong.
>
> For thermal zones with tzp->no_hwmon set, this is always true.
>
> We should add an extra check for that.

OK, can you please send a patch fixing all this mess?