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

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Message-ID: <f8c436ae-0f4c-5d2e-51a8-0e856fbf8f44@linaro.org>
Date:   Tue, 17 Nov 2020 09:57:29 +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 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.

> thanks,
> rui
> 
>>  	spin_lock(&stats->lock);
>>  
>>  	if (stats->state == new_state)
> 


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