CVE-2021-47318 is a use-after-free vulnerability identified in the Linux kernel's architecture topology management code, specifically related to the handling of the scale_freq_data structure. The vulnerability arises in the function topology_scale_freq_tick(), which is invoked from scheduler_tick(). This function may use a pointer to scale_freq_data that has already been cleared by topology_clear_scale_freq_source(), leading to a use-after-free condition. The root cause is the lack of synchronization or protection mechanisms ensuring that once scale_freq_data is cleared, it is no longer accessed. The Linux kernel scheduler operates with high frequency and low latency requirements, so adding traditional locking mechanisms in scheduler_tick() is undesirable due to performance impacts. Instead, the fix employs the Read-Copy-Update (RCU) synchronization mechanism, which allows safe concurrent access and updates without heavy locking. The synchronize_rcu() call ensures that all pre-existing RCU read-side critical sections complete before the cleared data is freed, preventing use-after-free scenarios. This vulnerability affects Linux kernel versions identified by the provided commit hashes, and while no known exploits are currently reported in the wild, the flaw could potentially lead to kernel crashes or undefined behavior due to dereferencing freed memory. The vulnerability is technical and low-level, involving kernel scheduler internals and architecture topology frequency scaling data structures, which are critical for CPU performance management and scheduling.

For European organizations relying on Linux-based systems, this vulnerability could have several impacts. Exploitation could lead to kernel crashes (denial of service) or potentially escalate to privilege escalation if an attacker can manipulate scheduler behavior or kernel memory. Systems with high availability requirements, such as servers in financial institutions, telecommunications, or critical infrastructure, could experience outages or degraded performance. Since Linux is widely used in European data centers, cloud environments, and embedded systems, the vulnerability could affect a broad range of sectors. However, exploitation complexity is moderate as it requires triggering scheduler ticks and manipulating kernel internals, which may limit widespread exploitation. Still, organizations running custom or older Linux kernels without patches are at risk. The vulnerability could also impact embedded Linux devices used in industrial control systems or IoT deployments common in Europe, potentially affecting operational technology environments.

European organizations should prioritize updating their Linux kernels to versions that include the patch addressing CVE-2021-47318. Since the fix involves kernel-level synchronization changes, applying vendor-provided kernel updates or mainline kernel patches is essential. For environments where immediate patching is challenging, organizations should monitor kernel scheduler behavior and system logs for anomalies or crashes related to scheduler_tick(). Employing kernel live patching solutions (such as kpatch or kgraft) can reduce downtime when applying fixes. Additionally, organizations should restrict unprivileged access to kernel interfaces and ensure that only trusted code runs with kernel-level privileges to reduce the risk of exploitation. Security teams should also maintain robust monitoring and incident response capabilities to detect potential exploitation attempts. Finally, testing kernel updates in staging environments before production deployment is recommended to avoid regressions.