CVE-2023-53522

Root

Cause

CVE-2023-53522 is a locking order inversion vulnerability in the Linux kernel's cgroup freezer subsystem. The issue was introduced by commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic"), which replaced an atomic_inc() in freezer_apply_state() with static_branch_inc(). The latter internally acquires cpu_hotplug_lock, creating a circular locking dependency with freezer_mutex [1][2].

Exploitation

Path

An attacker with local access and the ability to write to cgroup files can trigger the deadlock. The lock chain is: cpu_hotplug_lock → cgroup_threadgroup_rwsem → freezer_mutex (via cgroup_procs_write), and in the opposite direction: freezer_mutex → cpu_hotplug_lock (via freezer_write). When both paths execute concurrently, a deadlock occurs [1][2].

Impact

A successful exploitation leads to a system hang (deadlock), resulting in a denial of service (DoS). The CVSS v3 score is 7.8 (High), reflecting the potential for complete system unavailability. No privilege escalation or data compromise is described.

Mitigation

The fix swaps the locking order by moving cpus_read_lock() in freezer_apply_state() to before mutex_lock(&freezer_mutex) in freezer_change_state(). Patches have been applied to the stable kernel trees as commits 34fbb7b45bae and 57dcd64c7e03 [1][2]. Users should update to a kernel version containing these commits.