linux-kernel - Re: [PATCH] PM: EM: Fix NULL pointer dereference in em_create

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Message-ID: <CAJZ5v0iB2fqiab2Uj7Et_+qztx208cFKHuS7e_Y9ATmgr09jyw@mail.gmail.com>
Date: Thu, 15 Jan 2026 21:30:52 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Malaya Kumar Rout <mrout@...hat.com>, lukasz.luba@....com
Cc: malayarout91@...il.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM: EM: Fix NULL pointer dereference in em_create_pd()

On Thu, Jan 15, 2026 at 11:37 AM Malaya Kumar Rout <mrout@...hat.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@...hat.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?

> +                       }
>                         cpu_dev->em_pd = pd;
>                 }
>
> --