linux-kernel - Re: [PATCH] thermal: Fix NULL pointer dereference issue

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Message-ID: <ae8a6805-7071-269d-f49a-7e1051cfb399@linaro.org>
Date:   Tue, 17 Nov 2020 13:08:59 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Zhang Rui <rui.zhang@...el.com>,
        Mukesh Ojha <mojha@...eaurora.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     amitk@...nel.org
Subject: Re: [PATCH] thermal: Fix NULL pointer dereference issue

On 17/11/2020 12:27, Zhang Rui wrote:
> On Tue, 2020-11-17 at 09:57 +0100, Daniel Lezcano wrote:
>> On 17/11/2020 08:18, Zhang Rui wrote:
>>> On Mon, 2020-11-16 at 21:59 +0530, Mukesh Ojha wrote:
>>>> Cooling stats variable inside
>>>> thermal_cooling_device_stats_update()
>>>> can get NULL. We should add a NULL check on stat inside for
>>>> sanity.
>>>>
>>>> Signed-off-by: Mukesh Ojha <mojha@...eaurora.org>
>>>> ---
>>>>  drivers/thermal/thermal_sysfs.c | 3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/thermal/thermal_sysfs.c
>>>> b/drivers/thermal/thermal_sysfs.c
>>>> index a6f371f..f52708f 100644
>>>> --- a/drivers/thermal/thermal_sysfs.c
>>>> +++ b/drivers/thermal/thermal_sysfs.c
>>>> @@ -754,6 +754,9 @@ void
>>>> thermal_cooling_device_stats_update(struct
>>>> thermal_cooling_device *cdev,
>>>>  {
>>>>  	struct cooling_dev_stats *stats = cdev->stats;
>>>>  
>>>> +	if (!stats)
>>>> +		return;
>>>> +
>>>
>>> May I know in which case stats can be NULL?
>>> The only possibility I can see is that cdev->ops->get_max_state()
>>> fails
>>> in cooling_device_stats_setup(), right?
>>
>> A few lines below, the allocation could fail.
>>
>>         stats = kzalloc(var, GFP_KERNEL);
>>         if (!stats)
>>                 return;
>>
>> Some drivers define themselves as a cooling device state to let the
>> userspace to act on their power. The screen brightness is one example
>> with a cdev with 1024 states, the resulting stats table to be
>> allocated
>> is very big and the kzalloc is prone to fail.
>>
> Oh, right.
> As we're not going to fix the cdev, so I think we do need this patch,
> right?

If the allocation fails at this level if initialization there is clearly
something wrong. I'm wondering if it would make sense to report back an
error and make thermal_cooling_device_register to fail.

Having an allocation failing and silently ignore it sounds like not very
robust IMO.




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