Re: OOB access on ACPI processor thermal device via sysfs write

[Rafael J. Wysocki]

On Thursday, April 2, 2020 12:03:30 PM CEST Zhang Rui wrote:
> On Thu, 2020-04-02 at 11:03 +0200, Takashi Iwai wrote:
> > On Thu, 02 Apr 2020 09:47:50 +0200,
> > Zhang, Rui wrote:
> > > 
> > > CC Viresh.
> > > 
> > > Yes, I've received it.
> > > 
> > > To me, there is not a hard rule that the cooling device max_state
> > > must be static.
> > > We should be able to detect the max_state change and reset the
> > > stats table when necessary.
> > > 
> > > I just finished a prototype patch to do so, and will paste it
> > > later.
> > 
> > Great, that sounds like a feasible option, indeed.
> > 
> > 
> Please try the patch below and see if the problem goes away or not.
> 
> From 7b429674a0e1a6226734c8919b876bb57d946b1d Mon Sep 17 00:00:00 2001
> From: Zhang Rui <rui.zhang@xxxxxxxxx>
> Date: Thu, 2 Apr 2020 11:18:44 +0800
> Subject: [RFC PATCH] thermal: update thermal stats table when max cooling
>  state changed
> 
> The maximum cooling state of a cooling device may be changed at
> runtime. Thus the statistics table must be updated to handle the real
> maximum cooling states supported.
> 
> This fixes an OOB issue when updating the statistics of the processor
> cooling device, because it only supports 1 cooling state before cpufreq
> driver loaded.

It might also be addressed by adding a ->get_state_count() callback to
struct thermal_cooling_device_ops (and fall back to ->get_max_state() if
that is NULL) and use that for the stats allocation.

If the new callback always returns CPUFREQ_THERMAL_MAX_STEP, the size of the
stats table will be sufficient in all cases and acpi_processor_notifier()
can update it as needed.