[PATCH] thermal: Fix NULL pointer dereference issue

[PATCH] thermal: Fix NULL pointer dereference issue

[Mukesh Ojha]

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;
+
 	spin_lock(&stats->lock);
 
 	if (stats->state == new_state)
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project

Re: [PATCH] thermal: Fix NULL pointer dereference issue

[Zhang Rui]

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?

thanks,
rui

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

Re: [PATCH] thermal: Fix NULL pointer dereference issue

[Daniel Lezcano]

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.

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


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Re: [PATCH] thermal: Fix NULL pointer dereference issue

[Zhang Rui]

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?

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

Re: [PATCH] thermal: Fix NULL pointer dereference issue

[Daniel Lezcano]

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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