CVE-2026-99065: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus() With commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug processing synchronous"), the cpuset hotplug operation becomes synchronous. That commit also removes the code that handles race between cpuset_hotplug_work and cpu hotplug notifier with the assumption that race is now gone. Later commit 7a0aabd9ce69 ("cgroup/cpuset: Always use cpu_active_mask") updates the cpuset code to always use cpu_active_mask instead of cpu_online_mask in some places including guarantee_online_cpus() which is renamed to guarantee_active_cpus() in that commit. In the case of CPU offline operation, cpu_active_mask is updated first in sched_cpu_deactivate() to remove the offline CPU before cpuset_handle_hotplug() is called to update the effective_cpus of the affected cpusets. The cpu_online_mask is updated after that near the end of the offline operation to remove the offline CPU. As a result, the race comes back and the top cpuset may not have any active CPU leading to NULL pointer dereference during the race window when guarantee_active_cpus() is called after cpu_active_mask is updated to remove the CPU to be torn down but before cpuset_handle_hotplug() is able to properly update the effective_cpus of the top cpuset. Fix this by adding back the NULL cs check to avoid this problem.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 7a0aabd9ce697fc581ec691b21f748050fbcf004, < 8d88d3221204fbb1b6dc2c0f2f2181fe49126639; >= 7a0aabd9ce697fc581ec691b21f748050fbcf004, < a21c255159bfe0034740292e10d2e258feeeb10d; >= 7a0aabd9ce697fc581ec691b21f748050fbcf004, < 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2
Linux	Linux	6.16

References

Timeline

Published: Oct 23, 2026
Last Modified: Oct 23, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-99065?

In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus() With commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug processing synchronous"), the cpuset hotplug operation becomes synchronous. That commit also removes the code that handles race between cpuset_hotplug_work and cpu hotplug notifier with the assumption that race is now gone. Later commit 7a0aabd9ce69 ("cgroup/cpuset: Always use cpu_active_mask") updates the cpuset code to always use cpu_active_mask instead of cpu_online_mask in some places including guarantee_online_cpus() which is renamed to guarantee_active_cpus() in that commit. In the case of CPU offline operation, cpu_active_mask is updated first in sched_cpu_deactivate() to remove the offline CPU before cpuset_handle_hotplug() is called to update the effective_cpus of the affected cpusets. The cpu_online_mask is updated after that near the end of the offline operation to remove the offline CPU. As a result, the race comes back and the top cpuset may not have any active CPU leading to NULL pointer dereference during the race window when guarantee_active_cpus() is called after cpu_active_mask is updated to remove the CPU to be torn down but before cpuset_handle_hotplug() is able to properly update the effective_cpus of the top cpuset. Fix this by adding back the NULL cs check to avoid this problem.

How severe is CVE-2026-99065?

Severity scoring for CVE-2026-99065 is pending analysis.

How do I fix CVE-2026-99065?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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