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

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Date:   Wed, 29 Mar 2023 18:03:26 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 5:59 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 29/03/2023 16:38, Rafael J. Wysocki wrote:
> > On Wed, Mar 29, 2023 at 4:16 PM Daniel Lezcano
> > <daniel.lezcano@...aro.org> wrote:
> >>
> >> 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.
> >
> > But it's there in my thermal branch already.
> >
> > Do you want to revert the thermal_hwmon.c part of commit dec07d399cc8?
>
> Oh, right. Fair enough.
>
> I think Rui's patch is fine then.

I guess you mean the $subject one, that is:

https://patchwork.kernel.org/project/linux-pm/patch/20230329090055.7537-1-rui.zhang@intel.com

What about the message printed when temp is NULL.  Should the original
form of it be restored too?


> >> 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 ?
> >
> > IMV whoever is allowed to use a thermal zone pointer should also be
> > allowed to print messages related to its use, especially debug ones.
> >
> > "Encapsulation" means that the members of a thermal zone device object
> > should not be accessed directly by its users other than the core, not
> > that it cannot be used as a message tag.
>
> Actually it is not about the encapsulation but the namespace of the
> messages. If a driver has an issue, IMO it is better it uses the device
> related messages and let thermal zone messages to be related to what is
> happening in the thermal framework, not in the back end.
>
>
>
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