rust: cpufreq: reject NULL from cpufreq_cpu_get()

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")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Mehmet Koseoglu <mehmet.mkoseoglu@gmail.com>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: spidermana <xuyiwen14@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

0 files changed, 0 insertions, 0 deletions