Re: [PATCH] thermal: gov_power_allocator: Fix NULL pointer dereference in update_tz()

[Lukasz Luba <lukasz.luba@arm.com>]

On 8/22/26 12:42, Sumeet Pawnikar wrote:
> power_allocator_update_tz() unconditionally derives the trip descriptor of
> params->trip_max as below,
>    const struct thermal_trip_desc *td = trip_to_trip_desc(params->trip_max);
> and then walks td->thermal_instances. However, params->trip_max is allowed
> to be NULL and in that case the list walk dereferences a bogus pointer
> derived from NULL which oops the kernel.
> 
> get_governor_trips() picks trip_switch_on and trip_max out of the trip
> table of the zone. When the zone has neither a passive nor an active trip
> point, last_active is NULL and params->trip_max is left NULL. This is an
> explicitly supported configuration, as documented in the function
> get_governor_trips() as below,
>    If there are no passive or active trip points, then the governor won't
>    do anything. In fact, its throttle function won't be called at all.
> 
> Return early from power_allocator_update_tz() when params->trip_max is NULL
> and only compute the trip descriptor after that check. There is nothing to
> update in that case anyway, with no trip_max and there are no thermal
> instances for the governor to account for, num_actors stays zero and
> total_weight is irrelevant.
> 
> Fixes: 912e97c67cc3 ("thermal: gov_power_allocator: Move memory allocation out of throttle()")
> 
> Signed-off-by: Sumeet Pawnikar <sumeet4linux@gmail.com>
> ---
>   drivers/thermal/gov_power_allocator.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
> index 37f2e22a999e..b5c254187628 100644
> --- a/drivers/thermal/gov_power_allocator.c
> +++ b/drivers/thermal/gov_power_allocator.c
> @@ -660,10 +660,15 @@ static void power_allocator_update_tz(struct thermal_zone_device *tz,
>   				      enum thermal_notify_event reason)
>   {
>   	struct power_allocator_params *params = tz->governor_data;
> -	const struct thermal_trip_desc *td = trip_to_trip_desc(params->trip_max);
> +	const struct thermal_trip_desc *td;
>   	struct thermal_instance *instance;
>   	int num_actors = 0;
>   
> +	if (!params->trip_max)
> +		return;
> +
> +	td = trip_to_trip_desc(params->trip_max);
> +
>   	switch (reason) {
>   	case THERMAL_TZ_BIND_CDEV:
>   	case THERMAL_TZ_UNBIND_CDEV:


LGTM,

Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>