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

[Daniel Lezcano]

On 29/03/2023 14:06, Rafael J. Wysocki wrote:
> On Wed, Mar 29, 2023 at 11:57 AM Daniel Lezcano
> <daniel.lezcano@xxxxxxxxxx> 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@xxxxxxxxx>
> > > Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
> > > ---
> > > 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.

Actually we previously said the thermal_hwmon can be considered as part 
of the thermal core code, so we can keep using tz->device.

I'll drop this change from the series.

On the other side, adding more thermal_zone_debug/info.. gives 
opportunities to external components of the core thermal framework to 
write thermal zone device related message. I'm not sure that is a good 
thing, each writer should stay in its namespace, no ?

> > > ---
> > >    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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