CVE-2026-92492 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
cpufreq/amd-pstate: handle missing policy in dynamic EPP callbacks
cpufreq_cpu_get() returns NULL when no cpufreq policy is associated with the requested CPU, for example because the CPU is offline or the policy has already been torn down. Both amd_pstate_power_supply_notifier() and amd_pstate_profile_set() acquire a policy via cpufreq_cpu_get() and then pass that pointer to amd_pstate_get_balanced_epp() and amd_pstate_set_epp(), which dereference it unconditionally. A racing CPU hotplug or driver teardown can therefore lead to a NULL pointer dereference on either of these dynamic EPP paths.
The third cpufreq_cpu_get() caller in this file, amd_pstate_verify(), already handles the NULL case. Bring the two new callers in line with that pattern: return NOTIFY_OK from the power-supply notifier (matching the other "nothing to do" exits) and -ENODEV from amd_pstate_profile_set() (the usual cpufreq error for a missing CPU policy).
Found by code inspection; not tested on hardware.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's AMD P-State driver contains a critical null pointer dereference vulnerability within its dynamic Energy Performance Preference callbacks, specifically affecting the amd_pstate_power_supply_notifier and amd_pstate_profile_set functions. This flaw arises from an improper handling of CPU policy lifecycle management during concurrent operations such as hotplug events or driver teardowns. The core issue stems from the use of cpufreq_cpu_get to retrieve a pointer to the current frequency scaling policy for a specific processor. Under normal circumstances, this function returns a valid structure representing the active configuration. However, if the target CPU is offline, being removed from the system, or if its associated policy has already been deallocated due to race conditions during shutdown sequences, cpufreq_cpu_get correctly returns NULL to indicate that no such policy exists.
The technical flaw lies in the subsequent unconditional dereferencing of this pointer within amd_pstate_get_balanced_epp and amd_pstate_set_epp. When these functions receive a null pointer instead of a valid policy structure, they attempt to access memory fields or invoke methods on an invalid address. This results in a kernel panic or system crash because the operating system cannot safely execute instructions against a non-existent object in memory. The vulnerability is particularly insidious because it relies on timing-dependent race conditions where hardware state changes occur simultaneously with software-driven policy updates, making it difficult to reproduce consistently without specific stress testing scenarios involving rapid CPU online-offline transitions.
From an operational impact perspective, this null pointer dereference can lead to immediate system instability and denial of service for the affected node in a cluster environment or complete host unavailability if running on bare metal hardware. An attacker with local access could potentially trigger these race conditions by rapidly toggling CPU states or manipulating power supply notifications to force the driver into an inconsistent state where it attempts to manage resources that no longer exist. While the vulnerability was identified through static code inspection rather than dynamic testing, its presence represents a significant reliability risk for systems relying on AMD P-State technology for fine-grained energy management and performance scaling.
The remediation strategy involves aligning the error handling logic of these two affected functions with the existing pattern established in amd_pstate_verify, which already correctly checks for null returns from cpufreq_cpu_get. For the power supply notifier callback, the fix requires returning NOTIFY_OK when no policy is found, effectively treating the absence of a CPU as a non-event that does not require further processing or state modification. This approach ensures that transient offline states do not trigger fatal errors while maintaining the integrity of the notification chain. Conversely, for amd_pstate_profile_set, which operates in a different context requiring explicit error signaling to user space or upper kernel layers, the function must return -ENODEV upon detecting a null policy pointer. This standard errno value clearly communicates that no device is available for the requested operation, allowing calling functions to handle the absence gracefully rather than crashing.
This vulnerability maps directly to CWE-476, which describes NULL Pointer Dereference vulnerabilities where software incorrectly handles references that are not valid pointers. In terms of attack vectors and behavioral classification within the MITRE ATT&CK framework, this flaw aligns with T1059 Command and Scripting Interpreter if an attacker leverages local privilege escalation to manipulate system states, though more accurately it falls under resource exhaustion or denial-of-service techniques related to kernel-level stability attacks. The lack of proper input validation regarding the existence of hardware resources before dereferencing them is a classic example of insufficient defensive coding practices in low-level driver development.
To mitigate this risk, developers must ensure that all code paths interacting with cpufreq policies perform rigorous null checks immediately after retrieval operations. It is essential to treat CPU hotplug events and driver unload sequences as critical points where resource availability cannot be assumed. By implementing consistent error handling across all entry points in the amd-pstate module, the kernel maintains stability even under high-concurrency scenarios involving dynamic hardware configuration changes. This patch not only resolves the immediate crash risk but also improves the overall robustness of the AMD P-State driver by enforcing strict adherence to policy lifecycle rules throughout its execution flow.