In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on… (CVE-2026-98542)

The Linux kernel vulnerability CVE-2026-98542 involves the cgroup cpuset subsystem where remote_partition_enable() failed to properly handle conflicts between CPUs assigned to remote partitions and those already exclusively owned by ancestor local partitions. A previous commit replaced an error check with a warning, allowing remote_partition_enable() to proceed despite CPU conflicts, resulting in multiple active root partitions claiming exclusive use of the same CPU. The fix restores the error return PERR_NOCPUS when new CPUs intersect with subpartitions_cpus, matching the behavior of remote_cpus_update(), and includes a regression test to prevent recurrence.

This vulnerability can lead to inconsistent CPU partitioning states where multiple partitions claim exclusive control over the same CPU, potentially causing resource management issues within the kernel's cgroup cpuset subsystem. There is no indication of direct security exploitation or privilege escalation in the provided data.

A fix has been implemented that returns an error (PERR_NOCPUS) when CPU conflicts occur in remote_partition_enable(), preventing overlapping exclusive CPU assignments. Users should update to the Linux kernel version that includes this fix (post Linux 7.3.0-rc3). No additional mitigation steps are indicated.