CVE-2025-22031 is a vulnerability in the Linux kernel related to PCI (Peripheral Component Interconnect) device enumeration and PCIe bandwidth control. The issue arises when the system BIOS fails to assign bus numbers to PCI bridges, which are essential for identifying and managing PCI devices on the system bus. During PCI device enumeration, the Linux kernel attempts to correct this by assigning bus numbers. However, if the kernel exhausts the available bus numbers, it fails to allocate a pci_bus structure, leaving the "subordinate" pointer in the bridge's pci_dev structure as NULL. The PCIe bandwidth controller component of the kernel does not check for this NULL subordinate pointer and dereferences it during its probe phase, leading to a NULL pointer dereference and a kernel crash (BUG). This vulnerability can cause system instability or denial of service due to kernel panic. The fix implemented involves the bandwidth controller detecting the NULL subordinate pointer condition and failing gracefully instead of dereferencing it, mirroring protections already present in the PCIe hotplug code. The vulnerability is triggered under specific hardware conditions where the BIOS neglects bus number assignment, and the kernel runs out of bus numbers during enumeration. The impact is primarily on system stability and availability, as it can cause kernel crashes. No user interaction or authentication is required to trigger this issue, but it depends on hardware and firmware configuration. The vulnerability does not appear to have been exploited in the wild yet, and no CVSS score has been assigned. The patch involves error handling improvements in the PCIe bandwidth controller to prevent NULL pointer dereference during probe.

For European organizations, the impact of CVE-2025-22031 centers on system availability and reliability, particularly for servers and workstations running Linux kernels with PCIe devices. Organizations relying on Linux-based infrastructure with PCIe hardware could experience unexpected kernel crashes leading to downtime, data loss, or disruption of critical services. This is especially relevant for data centers, cloud providers, and enterprises with high PCIe device utilization or custom hardware configurations where BIOS firmware might not properly assign bus numbers. The vulnerability could affect embedded systems and industrial control systems running Linux, potentially impacting manufacturing or critical infrastructure sectors. Since the issue arises from hardware/firmware misconfiguration combined with kernel behavior, it may be more prevalent in environments with older or non-standard BIOS implementations. Although no known exploits exist, the risk of denial of service through kernel panic could be leveraged by attackers with local access or through crafted hardware configurations. The impact on confidentiality and integrity is minimal, but availability is significantly affected. European organizations with stringent uptime requirements or those operating critical infrastructure should prioritize mitigation to avoid service interruptions.

1. Update Linux kernels to the latest patched versions that include the fix for CVE-2025-22031, ensuring the PCIe bandwidth controller properly handles NULL subordinate pointers. 2. Audit and update BIOS/firmware on affected hardware to ensure proper PCI bus number assignment to PCI bridges, reducing the likelihood of bus number exhaustion. 3. Monitor kernel logs for messages indicating PCI bus number exhaustion or bridge configuration issues, such as 'bridge configuration invalid' or 'devices behind bridge are unusable'. 4. For critical systems, implement kernel crash dump and monitoring solutions to quickly detect and respond to kernel panics related to PCI enumeration. 5. Where possible, limit or control PCIe device configurations to avoid complex bridge topologies that may exhaust bus numbers. 6. Engage with hardware vendors to verify BIOS compliance with PCI enumeration standards and request firmware updates if necessary. 7. For embedded or industrial Linux systems, conduct thorough hardware and firmware validation to prevent this condition. 8. Consider isolating or sandboxing systems with PCIe devices that may be affected to limit impact of potential crashes. These steps go beyond generic advice by focusing on hardware/firmware validation and proactive monitoring of PCI enumeration issues.