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

[Zhang, Rui]

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@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.
> 
> > ---
> >   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.

thanks,
rui