CVE-2024-49927 addresses a vulnerability in the Linux kernel's x86 architecture IO-APIC interrupt allocation code. Specifically, the issue arises in the handling of allocation failures for IRQ pin lists during runtime, which can cause the kernel to panic unnecessarily. The panic occurs in the function __add_pin_to_irq_node() wrapped by a panic wrapper, triggered when the kernel fails to allocate an interrupt request (IRQ) pin, producing error messages such as "can not alloc irq_pin_list (-1,0,20)" and "Kernel panic - not syncing: IO-APIC: failed to add irq-pin." This panic is considered a leftover from historic IO/APIC code that enforced a hard failure during early boot if interrupt allocation failed. However, the affected code path is not critical enough to justify a kernel panic during runtime. The timer_check() code related to PIT/HPET timers, which determines if timer interrupts are delivered through IO/APIC, does not require interrupt allocation failure to cause a panic; it can either fallback to legacy timer modes or handle failure gracefully. The fix removes the panic wrapper around __add_pin_to_irq_node() and modifies mp_irqdomain_alloc() to handle allocation failures gracefully without causing a kernel panic. This change improves system stability by preventing unnecessary crashes due to IRQ allocation failures, which can occur under certain runtime conditions such as stress testing with failslab. The vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and is relevant to x86 platforms using IO-APIC interrupt controllers. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability primarily impacts the stability and availability of Linux-based systems running on x86 hardware that utilize IO-APIC for interrupt management. Many enterprise servers, cloud infrastructure, and embedded systems in Europe run Linux kernels with IO-APIC support. An unexpected kernel panic due to IRQ allocation failure can cause system downtime, disrupt critical services, and potentially lead to data loss if systems are not properly configured for failover or recovery. While this vulnerability does not directly compromise confidentiality or integrity, the availability impact can be significant for sectors relying on high uptime such as finance, healthcare, telecommunications, and public administration. Systems under heavy load or stress testing (e.g., using failslab tools) are more likely to encounter this issue. The fix enhances robustness by preventing unnecessary panics, thus improving operational continuity. European organizations with large Linux deployments, especially those using custom or older kernel versions, should prioritize patching to avoid unexpected outages. Since no known exploits exist, the immediate risk of targeted attacks is low, but unpatched systems remain vulnerable to stability issues.

1. Apply the official Linux kernel patch that removes the panic wrapper around __add_pin_to_irq_node() and updates mp_irqdomain_alloc() to handle IRQ allocation failures gracefully. Ensure kernel versions are updated to include this fix. 2. For organizations using custom or long-term support (LTS) kernels, backport the patch to maintain stability without waiting for full kernel upgrades. 3. Conduct thorough testing in staging environments, especially under stress conditions (e.g., failslab), to verify that the fix prevents kernel panics without introducing regressions. 4. Monitor kernel logs for IRQ allocation failures and panics to detect any residual issues or related hardware problems. 5. Implement robust system monitoring and alerting to quickly respond to any kernel panics or system crashes. 6. Consider fallback configurations for timer interrupts (PIT/HPET) to legacy modes as a contingency if IO-APIC issues persist. 7. Maintain updated hardware firmware and drivers to minimize IRQ allocation conflicts. 8. Educate system administrators about this issue to ensure rapid deployment of patches and awareness of symptoms.