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

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Date:   Tue, 17 Nov 2020 19:27:47 +0800
From:   Zhang Rui <rui.zhang@...el.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        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 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?

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