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Subject: Re: [PATCH] thermal: Fix NULL pointer dereference issue
To:     Zhang Rui <rui.zhang@intel.com>,
        Mukesh Ojha <mojha@codeaurora.org>, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     amitk@kernel.org
References: <1605544181-5348-1-git-send-email-mojha@codeaurora.org>
 <4e28affd89ba8a852e0fb7ace076458b3d43839a.camel@intel.com>
 <f8c436ae-0f4c-5d2e-51a8-0e856fbf8f44@linaro.org>
 <fd11744b16a91428303fe848ef8f72fd8f5c9a5e.camel@intel.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <ae8a6805-7071-269d-f49a-7e1051cfb399@linaro.org>
Date:   Tue, 17 Nov 2020 13:08:59 +0100
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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@codeaurora.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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