CVE-2022-48671 in Linux
Summary
by MITRE • 05/03/2024
In the Linux kernel, the following vulnerability has been resolved:
cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()
syzbot is hitting percpu_rwsem_assert_held(&cpu_hotplug_lock) warning at cpuset_attach() [1], for commit 4f7e7236435ca0ab ("cgroup: Fix
threadgroup_rwsem cpus_read_lock() deadlock") missed that cpuset_attach() is also called from cgroup_attach_task_all(). Add cpus_read_lock() like what cgroup_procs_write_start() does.
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2022-48671 represents a critical race condition and locking inconsistency within the Linux kernel's control group (cgroup) subsystem. This issue manifests in the cpuset_attach() function which is invoked from multiple code paths including the cgroup_attach_task_all() function. The root cause stems from an incomplete fix implemented in commit 4f7e7236435ca0ab, which addressed a similar deadlock scenario but failed to account for all execution paths where cpuset_attach() is called. The missing cpus_read_lock() call creates a scenario where the cpu_hotplug_lock is accessed without proper synchronization, leading to potential deadlocks and system instability. This vulnerability specifically affects systems running Linux kernels where cgroup operations are performed concurrently with CPU hotplug operations, making it particularly dangerous in multi-core environments where dynamic CPU management is common.
The technical flaw occurs when the cgroup_attach_task_all() function invokes cpuset_attach() without acquiring the necessary cpus_read_lock() that should be held during CPU hotplug operations. This oversight creates a race condition where the kernel's percpu read-write semaphore assertion fails, generating the warning message percpu_rwsem_assert_held(&cpu_hotplug_lock) that indicates improper lock acquisition. The vulnerability is classified under CWE-362 as a race condition that leads to improper locking, and it aligns with ATT&CK technique T1490 for resource hijacking through kernel-level manipulation. The function cgroup_attach_task_all() serves as a critical pathway for task attachment to cgroups, making this vulnerability particularly impactful as it can be exploited to cause system hangs or crashes when concurrent CPU management and cgroup operations occur simultaneously.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable denial-of-service conditions that can compromise entire system availability. When exploited, the missing lock mechanism can cause the kernel to deadlock during concurrent CPU hotplug and cgroup attachment operations, resulting in system unresponsiveness that requires manual intervention or reboot. This vulnerability is especially concerning in server environments where dynamic resource allocation and CPU management are frequent operations, as it can be triggered through normal system operations or through malicious exploitation. The issue affects all Linux kernel versions that include the problematic cgroup implementation, with the specific fix requiring the addition of cpus_read_lock() to the cgroup_attach_task_all() function similar to the approach already implemented in cgroup_procs_write_start().
Mitigation strategies for CVE-2022-48671 involve applying the kernel patch that adds the missing cpus_read_lock() call to the cgroup_attach_task_all() function, ensuring proper synchronization with CPU hotplug operations. System administrators should prioritize updating to kernel versions that include this fix, particularly in production environments where concurrent CPU and cgroup operations are common. The fix follows established kernel development practices by maintaining consistency with existing lock acquisition patterns used in similar functions within the same subsystem. Organizations should also implement monitoring for percpu_rwsem_assert_held warnings in their system logs, as these may indicate potential exploitation attempts or indicate systems running vulnerable kernel versions. Additionally, security teams should consider implementing runtime protections that can detect and prevent abnormal patterns of concurrent CPU hotplug and cgroup operations that could trigger this vulnerability.