CVE-2026-98542

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

cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict

When a remote partition is created underneath an existing local partition via a non-partition (PRS_MEMBER) intermediate cgroup, update_prstate() sees parent->partition_root_state == PRS_MEMBER and calls remote_partition_enable().

Commit 86888c7bd117 (cgroup/cpuset: Add warnings to catch inconsistency in exclusive CPUs) replaced the cpumask_intersects(tmp->new_cpus, subpartitions_cpus) error check in remote_partition_enable() with WARN_ON_ONCE(). As a result, remote_partition_enable() emits a warning and proceeds to enable the remote partition on CPUs that are already owned by the ancestor local partition in subpartitions_cpus.

This can be reproduced on Linux 7.3.0-rc3 with:

mkdir -p /tmp/cg1 mount -t cgroup2 none /tmp/cg1 echo +cpuset > /tmp/cg1/cgroup.subtree_control

mkdir /tmp/cg1/A echo 1 > /tmp/cg1/A/cpuset.cpus echo 1 > /tmp/cg1/A/cpuset.cpus.exclusive echo root > /tmp/cg1/A/cpuset.cpus.partition echo +cpuset > /tmp/cg1/A/cgroup.subtree_control

mkdir /tmp/cg1/A/B echo 1 > /tmp/cg1/A/B/cpuset.cpus echo 1 > /tmp/cg1/A/B/cpuset.cpus.exclusive echo +cpuset > /tmp/cg1/A/B/cgroup.subtree_control

mkdir /tmp/cg1/A/B/D echo 1 > /tmp/cg1/A/B/D/cpuset.cpus echo 1 > /tmp/cg1/A/B/D/cpuset.cpus.exclusive echo root > /tmp/cg1/A/B/D/cpuset.cpus.partition

which triggers:

WARNING: kernel/cgroup/cpuset.c:1594 at remote_partition_enable+0x1c1/0x300

and leaves both /tmp/cg1/A and /tmp/cg1/A/B/D as active root partitions claiming exclusive CPU 1.

Fix this by returning PERR_NOCPUS when tmp->new_cpus intersects subpartitions_cpus in remote_partition_enable(), matching the error code used by remote_cpus_update() for the same subpartitions_cpus conflict, and add a regression test case to tools/testing/selftests/cgroup/test_cpuset_prs.sh.

Tested in QEMU on Linux 7.3.0-rc3 using the reproducer above and tools/testing/selftests/cgroup/test_cpuset_prs.sh.

Affected Software

References

• https://git.kernel.org/stable/c/0751ab665cb3dcdac224b002565f2e28461740d5
• https://git.kernel.org/stable/c/241e67b60308cdce25bba66616a109759edd1d40
• https://git.kernel.org/stable/c/31c88350b7dd1522792f726f79607f31bb55c50f