Re: [PATCH] PM: EM: Fix NULL pointer dereference in em_create_pd()

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

On 1/15/26 20:30, Rafael J. Wysocki wrote:
> On Thu, Jan 15, 2026 at 11:37 AM Malaya Kumar Rout <mrout@redhat.com> wrote:
>>
>> The get_cpu_device() function can return NULL if the CPU device is
>> not registered. However, the code in em_create_pd() dereferences the
>> returned pointer without checking for NULL, which can lead to a kernel
>> panic during energy model initialization.
>>
>> Add a NULL check before dereferencing cpu_dev. If get_cpu_device()
>> returns NULL, return -ENODEV and properly clean up allocated resources
>> through the existing error path.
>>
>> This issue was found by code inspection. The same function is correctly
>> handled with NULL checking in em_cpu_get() at line 555-557.
>>
>> Fixes: 1bc138c62295 ("PM / EM: add support for other devices than CPUs in Energy Model")
>> Signed-off-by: Malaya Kumar Rout <mrout@redhat.com>
>> ---
>>   kernel/power/energy_model.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index 11af9f64aa82..3971743d7e67 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -466,6 +466,10 @@ static int em_create_pd(struct device *dev, int nr_states,
>>          if (_is_cpu_device(dev))
>>                  for_each_cpu(cpu, cpus) {
>>                          cpu_dev = get_cpu_device(cpu);
>> +                       if (!cpu_dev) {
>> +                               ret = -ENODEV;
>> +                               goto free_pd_table;
> 
> No, you need to clear em_pd for the CPUs for which it has been set already.
> 
> Maybe it would be better to do this check upfront for all CPUs in the
> mask.  Lukasz?
> 

Right, let me study this and come back with the recommendation...