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

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Message-ID: <CAJZ5v0hGnoEhYadoK-KPTvMtvviOrGqbY9jrmOUzTjOGe_rB_A@mail.gmail.com>
Date:   Wed, 29 Mar 2023 14:06:34 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org,
        rafael.j.wysocki@...el.com, 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 11:57 AM Daniel Lezcano
<daniel.lezcano@...aro.org> 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.

So maybe instead of the wholesale switch to using "driver-specific"
device pointers for printing messages, something like
thermal_zone_debug/info/warn/error() taking a thermal zone pointer as
the first argument can be defined?

At least this particular bug could be avoided this way.

> > ---
> >   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;
>
>
>
> >               return;
> >       }
> >
>
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