CVE-2022-48892 is a use-after-free vulnerability in the Linux kernel's scheduler subsystem affecting the handling of CPU affinity masks. Specifically, the flaw exists in the dup_user_cpus_ptr() function, which accesses the user_cpus_ptr pointer without proper locking mechanisms. The vulnerability arises due to a race condition between sched_setaffinity() calls and process fork() operations. Since sched_setaffinity() can be invoked concurrently from different processes, the user_cpus_ptr may be cleared or modified while dup_user_cpus_ptr() is accessing it, leading to a use-after-free or potentially a double-free scenario. Initially, the issue was limited to the arm64 architecture due to locking changes introduced in commit 07ec77a1d4e8, but subsequent commits reintroduced the bug affecting all architectures. The root cause is the improper clearing and copying of user_cpus_ptr during task cloning and CPU affinity changes without adequate synchronization under pi_lock. The fix involves always clearing the user_cpus_ptr of newly cloned tasks before copying and checking the source task's user_cpus_ptr state under proper locking. This vulnerability can cause kernel memory corruption, potentially leading to system crashes or privilege escalation if exploited. However, no known exploits are currently reported in the wild, and the patch is not backported to stable kernel releases, requiring manual application of the updated dup_user_cpus_ptr() function for mitigation.

For European organizations, this vulnerability poses a significant risk to systems running vulnerable Linux kernel versions, especially on servers and infrastructure using arm64 and other architectures. Exploitation could lead to kernel memory corruption, resulting in system instability, crashes, or denial of service. More critically, attackers with local access could leverage this flaw to escalate privileges to kernel level, compromising system confidentiality and integrity. This is particularly concerning for data centers, cloud providers, and critical infrastructure operators relying on Linux-based systems. The absence of known exploits reduces immediate risk, but the vulnerability's nature makes it a high-value target for attackers aiming to gain persistent, privileged access. Organizations with high compliance requirements (e.g., GDPR) must consider the potential impact on data protection and system availability. Additionally, the lack of patches in stable kernel releases complicates timely remediation, increasing exposure duration.

European organizations should prioritize the following mitigation steps: 1) Identify and inventory all Linux systems running kernel versions including the affected commits, particularly those on arm64 and other architectures. 2) Apply the upstream patch by manually updating the dup_user_cpus_ptr() function as the fix is not backported to stable kernels; this may require kernel recompilation and thorough testing. 3) Restrict local access to critical systems to trusted users only, minimizing the risk of local exploitation. 4) Monitor kernel logs and system behavior for anomalies indicative of memory corruption or crashes. 5) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Control Flow Integrity (CFI) to reduce exploitation likelihood. 6) Maintain robust incident response plans to quickly address potential exploitation attempts. 7) Engage with Linux distribution vendors for backported patches or security advisories relevant to specific distributions used. 8) Consider deploying intrusion detection systems capable of detecting kernel-level anomalies. These measures go beyond generic patching advice by emphasizing manual patch application, access control, and proactive monitoring tailored to this specific kernel vulnerability.