CVE-2026-72016

Technical Description

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

cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()

On arm64, when booting with `maxcpus` greater than the number of present

CPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present'

but have not yet been registered via register_cpu(). Consequently,

the per-cpu device objects for these CPUs are not yet initialized.

In cpuhp_smt_enable(), the code iterates over all present CPUs. Calling

_cpu_up() for these unregistered CPUs eventually leads to

sysfs_create_group() being called with a NULL kobject (or a kobject

without a directory), triggering the following warning in

fs/sysfs/group.c:

WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181

[...]

Call trace:

internal_create_group+0x41c/0x4bc (P)

sysfs_create_group+0x18/0x24

topology_add_dev+0x1c/0x28

cpuhp_invoke_callback+0x104/0x20c

__cpuhp_invoke_callback_range+0x94/0x11c

_cpu_up+0x200

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References