Re: [PATCH] thermal: core: fix use-after-free due to init/cancel delayed_work race

[Mauricio Faria de Oliveira]

On 2026-03-25 11:28, Mauricio Faria de Oliveira wrote:
> On 2026-03-25 11:17, Mauricio Faria de Oliveira wrote:
>> Thanks for looking into this.
>> 
>> On 2026-03-25 09:47, Rafael J. Wysocki wrote:
>>> I can see the one between thermal_zone_device_unregister() and
>>> thermal_zone_device_resume(), but that can be addressed by adding a
>>> TZ_STATE_FLAG_EXIT check to the latter AFAICS.
>>
> 
> Please disregard this paragraph; I incorrectly read/wrote _resume()
> as thermal_zone_pm_complete() discussed above. The rest should be
> right. I'll review this and get back shortly.
>
>> In the example describe above and detailed below, apparently that
>> is not sufficient, if I'm not missing anything. See, if _resume()
>> is reached with thermal_list_lock held, thermal_zone_device_exit()
>> is waiting for thermal_list_lock before setting TZ_STATE_FLAG_EXIT,
>> thus a check for it in _resume() would find it clear yet.

Ok, similarly: 

Say, thermal_pm_notify() -> thermal_pm_notify_complete() ->
thermal_zone_pm_complete() 
run before thermal_zone_device_unregister() is called;
thermal_zone_device_resume()
starts, and by now thermal_zone_device_unregister() is called.

If thermal_zone_device_resume() wins the race over thermal_zone_exit()
for guard(thermal_zone(tz) (tz->lock), it sees TZ_STATE_FLAG_EXIT clear;
note its callees (eg, thermal_zone_device_init()) run with tz->lock
held,
so they see it clear as well.

So, thermal_zone_device_init() calls INIT_DELAYED_WORK(), everything
returns, tz->lock is released and the thermal_zone_device_unregister()
-> thermal_zone_exit() path can continue to run.

Only now thermal_zone_exit() sets TZ_STATE_FLAG_EXIT (too late),
returns.
cancel_delayed_work_sync() does not wait for
thermal_zone_device_resume()
due to INIT_DELAYED_WORK() in thermal_zone_device_init(); and kfree(tz).

Then, thermal_zone_device_resume() accesses tz and hits use-after-free.

Hope this clarifies. Please let me know your thoughts. Thanks!

-- 
Mauricio