Re: [PATCH v2] rust: cpufreq: reject NULL from cpufreq_cpu_get()

["Onur Özkan" <work@onurozkan.dev>]

On Fri, 28 Aug 2026 19:16:57 +0300
Mehmet Koseoglu <mehmet.mkoseoglu@gmail.com> wrote:

Hi Mehmet,

> cpufreq_cpu_get() returns either a referenced policy or NULL.
> PolicyCpu::from_cpu() passed its return value to from_err_ptr(), which
> rejects ERR_PTR values but accepts NULL.
> 
> If the lookup fails, Policy::from_raw_mut() therefore constructs a mutable
> reference from NULL. Dropping the resulting PolicyCpu then passes the
> invalid pointer to cpufreq_cpu_put(), causing an oops in kobject_put().
> 
> Reject NULL with NonNull before constructing the Policy reference. Return
> ENODEV instead.
> 
> A KUnit negative-control run reproduced the oops with the original
> conversion. The same test passed with this change. The reproducer is
> available on request.
> 
> Fixes: 6ebdd7c93177 ("rust: cpufreq: Extend abstractions for policy and driver ops")
> Assisted-by: LLM
> Signed-off-by: Mehmet Koseoglu <mehmet.mkoseoglu@gmail.com>

This should be tagged for stable:

	Cc: stable@vger.kernel.org

LGTM otherwise.

> ---
> Changes in v2:
> - Format modified imports using the kernel's vertical import style.
> 
>  rust/kernel/cpufreq.rs | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
> index affa2b9490ef..4b992ea9a0f0 100644
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -14,7 +14,13 @@
>      cpumask,
>      device::{Bound, Device},
>      devres,
> -    error::{code::*, from_err_ptr, from_result, to_result, Result, VTABLE_DEFAULT_ERROR},
> +    error::{
> +        code::*,
> +        from_result,
> +        to_result,
> +        Result,
> +        VTABLE_DEFAULT_ERROR, //
> +    },
>      ffi::{c_char, c_ulong},
>      prelude::*,
>      types::ForeignOwnable,
> @@ -29,7 +35,10 @@
>      marker::PhantomData,
>      ops::{Deref, DerefMut},
>      pin::Pin,
> -    ptr,
> +    ptr::{
> +        self,
> +        NonNull, //
> +    },
>  };
>  
>  use macros::vtable;
> @@ -687,12 +696,13 @@ fn clear_data<T: ForeignOwnable>(&mut self) -> Option<T> {
>  impl<'a> PolicyCpu<'a> {
>      fn from_cpu(cpu: CpuId) -> Result<Self> {
>          // SAFETY: It is safe to call `cpufreq_cpu_get` for any valid CPU.
> -        let ptr = from_err_ptr(unsafe { bindings::cpufreq_cpu_get(u32::from(cpu)) })?;
> +        let ptr =
> +            NonNull::new(unsafe { bindings::cpufreq_cpu_get(u32::from(cpu)) }).ok_or(ENODEV)?;
>  
>          Ok(Self(
>              // SAFETY: The `ptr` is guaranteed to be valid and remains valid for the lifetime of
>              // the returned reference.
> -            unsafe { Policy::from_raw_mut(ptr) },
> +            unsafe { Policy::from_raw_mut(ptr.as_ptr()) },
>          ))
>      }
>  }
> -- 
> 2.55.0