CVE-2024-31076 genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

What is CVE-2024-31076?

CVE-2024-31076 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 Jun 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

The absence of IRQD_MOVE_PCNTXT prevents immediate effectiveness of interrupt affinity reconfiguration via procfs. Instead, the change is deferred until the next instance of the interrupt being triggered on the original CPU.

When the interrupt next triggers on the original CPU, the new affinity is enforced within __irq_move_irq(). A vector is allocated from the new CPU, but the old vector on the original CPU remains and is not immediately reclaimed. Instead, apicd->move_in_progress is flagged, and the reclaiming process is delayed until the next trigger of the interrupt on the new CPU.

Upon the subsequent triggering of the interrupt on the new CPU, irq_complete_move() adds a task to the old CPU's vector_cleanup list if it remains online. Subsequently, the timer on the old CPU iterates over its vector_cleanup list, reclaiming old vectors.

However, a rare scenario arises if the old CPU is outgoing before the interrupt triggers again on the new CPU.

In that case irq_force_complete_move() is not invoked on the outgoing CPU to reclaim the old apicd->prev_vector because the interrupt isn't currently affine to the outgoing CPU, and irq_needs_fixup() returns false. Even though __vector_schedule_cleanup() is later called on the new CPU, it doesn't reclaim apicd->prev_vector; instead, it simply resets both apicd->move_in_progress and apicd->prev_vector to 0.

As a result, the vector remains unreclaimed in vector_matrix, leading to a CPU vector leak.

To address this issue, move the invocation of irq_force_complete_move() before the irq_needs_fixup() call to reclaim apicd->prev_vector, if the interrupt is currently or used to be affine to the outgoing CPU.

Additionally, reclaim the vector in __vector_schedule_cleanup() as well, following a warning message, although theoretically it should never see apicd->move_in_progress with apicd->prev_cpu pointing to an offline CPU.

Which versions are affected by CVE-2024-31076?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2024-31076?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2024-31076 being exploited?

There is no known exploitation of CVE-2024-31076 in the wild and no public exploit code.

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• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2024-31076, DEBIAN-CVE-2024-31076, GHSA-7362-fxfh-r4x4, UBUNTU-CVE-2024-31076.