powercap: dtpm_cpu: Fix NULL pointer dereference in get_pd_power_uw()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: powercap: dtpm_cpu: Fix NULL pointer dereference in get_pd_power_uw() The get_pd_power_uw() function can crash with a NULL pointer dereference when em_cpu_get() returns NULL. This occurs when a CPU becomes impossible during runtime, causing get_cpu_device() to return NULL, which propagates through em_cpu_get() and leads to a crash when em_span_cpus() dereferences the NULL pointer. Add a NULL check after em_cpu_get() and return 0 if unavailable, matching the existing fallback behavior in __dtpm_cpu_setup(). [ rjw: Drop an excess empty code line ]

References

• https://git.kernel.org/stable/c/27914f2b795e2b58e9506f281dcdd98fef09d3c2
• https://git.kernel.org/stable/c/c6ec27091cf5ac05094c1fe3a6ce914cf711a37c
• https://git.kernel.org/stable/c/8374ac7d69a57d737e701a851ffe980a0d27d3ad
• https://git.kernel.org/stable/c/27e0318f0ea69fcfa32228847debc384ade14578
• https://git.kernel.org/stable/c/2fd001a0075ac01dc64a28a8e21226b3d989a91d
• https://git.kernel.org/stable/c/46dc57406887dd02565cb264224194a6776d882b