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.
Published: 2026-10-23
Score: n/a
EPSS: n/a
KEV: No
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History

Fri, 23 Oct 2026 12:45:00 +0000

Type Values Removed Values Added
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.
Title cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-10-23T12:23:08.458Z

Reserved: 2026-09-25T10:25:14.389Z

Link: CVE-2026-99065

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-23T13:17:30.367

Modified: 2026-10-23T13:17:30.367

Link: CVE-2026-99065

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses

No weakness.