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

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Message-ID: <016dc073-c9a3-4b96-6c58-7b21e0f998a5@linaro.org>
Date:   Wed, 29 Mar 2023 16:16:01 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.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 29/03/2023 14:06, Rafael J. Wysocki wrote:
> 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.

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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