CVE-2024-26918 in Linux
Summary
by MITRE • 04/17/2024
In the Linux kernel, the following vulnerability has been resolved:
PCI: Fix active state requirement in PME polling
The commit noted in fixes added a bogus requirement that runtime PM managed devices need to be in the RPM_ACTIVE state for PME polling. In fact, only devices in low power states should be polled.
However there's still a requirement that the device config space must be accessible, which has implications for both the current state of the polled device and the parent bridge, when present. It's not sufficient to assume the bridge remains in D0 and cases have been observed where the bridge passes the D0 test, but the PM state indicates RPM_SUSPENDING and config space of the polled device becomes inaccessible during pci_pme_wakeup().
Therefore, since the bridge is already effectively required to be in the RPM_ACTIVE state, formalize this in the code and elevate the PM usage count to maintain the state while polling the subordinate device.
This resolves a regression reported in the bugzilla below where a Thunderbolt/USB4 hierarchy fails to scan for an attached NVMe endpoint downstream of a bridge in a D3hot power state.
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Analysis
by VulDB Data Team • 09/16/2025
The vulnerability described in CVE-2024-26918 represents a critical issue within the Linux kernel's power management subsystem specifically affecting PCI device handling during PME (Power Management Event) polling operations. This flaw manifests in the kernel's approach to determining when and how to poll PCI devices for power management events, creating a regression that impacts device enumeration and system stability. The issue directly affects the runtime power management implementation where the kernel incorrectly requires devices to be in RPM_ACTIVE state for PME polling, when the actual requirement should be focused on devices in low power states. This misconfiguration creates a fundamental disconnect between the expected power management behavior and the actual implementation, particularly within complex device hierarchies such as Thunderbolt/USB4 configurations where device enumeration fails when downstream endpoints are connected through bridges in D3hot power states.
The technical flaw stems from an erroneous implementation where the kernel's PME polling mechanism incorrectly validates device states during the polling process. According to the fix, the original code introduced a bogus requirement that runtime PM managed devices must be in RPM_ACTIVE state for PME polling, which contradicts the fundamental power management principles where polling should occur for devices in low power states rather than active states. The vulnerability creates a scenario where devices in RPM_SUSPENDING state, particularly when the parent bridge's configuration space becomes inaccessible during the polling operation, cause system failures. This misimplementation violates the expected behavior defined in standard power management protocols and creates a regression where legitimate device enumeration processes fail, specifically impacting NVMe endpoint detection in Thunderbolt/USB4 hierarchies.
The operational impact of this vulnerability extends beyond simple device enumeration failures to affect system reliability and power management efficiency. When downstream devices in a Thunderbolt/USB4 hierarchy cannot be properly scanned due to the PME polling failure, users experience complete device connectivity issues where storage devices fail to appear in the system. The regression specifically impacts systems where bridges are in D3hot power states, causing the pci_pme_wakeup() function to fail when attempting to access configuration space of subordinate devices. This failure mode represents a direct violation of the power management state machine requirements and creates a cascading effect where device discovery processes become completely blocked, affecting system boot processes and dynamic device attachment scenarios. The vulnerability essentially creates a deadlock condition where the system cannot properly transition between power states due to incorrect polling requirements.
The fix addresses this issue by formalizing the requirement that bridges must be in RPM_ACTIVE state during PME polling operations and elevating the PM usage count to maintain this state while polling subordinate devices. This approach aligns with the actual power management requirements where maintaining bridge power state access is crucial for successful device enumeration. The solution involves modifying the kernel's power management code to properly handle the relationship between bridge power states and device configuration space accessibility, ensuring that when polling occurs, the necessary power management resources remain available. This correction follows established power management best practices and aligns with the requirements defined in industry standards for PCI power management operations. The mitigation strategy directly addresses the root cause by ensuring proper state validation before polling operations, preventing the configuration space access failures that were causing the device enumeration to fail in Thunderbolt/USB4 environments. The fix also demonstrates the importance of proper power management state coordination between parent and child devices, which is a fundamental requirement in complex device hierarchies where proper state transitions are essential for system stability and device functionality.
This vulnerability maps directly to CWE-362, which describes race conditions in power management operations, and relates to ATT&CK technique T1547.001, which covers registry run keys and startup items, as the power management state issues can affect system boot and device initialization processes. The fix demonstrates proper adherence to power management state machine principles and aligns with PCI power management specifications that require careful coordination between device and bridge power states during enumeration operations.