CVE-2021-47254 is a use-after-free vulnerability identified in the Linux kernel's GFS2 (Global File System 2) component, specifically within the gfs2_glock_shrink_scan function. The vulnerability arises due to a race condition involving the GLF_LRU flag and the lru_lock synchronization mechanism. In detail, the GLF_LRU flag is used to track whether a glock (a lock structure in GFS2) is part of the least recently used (LRU) list. The vulnerability occurs because the flag is cleared under the lru_lock during the shrink scan path, but a conditional rescheduling function (cond_resched_lock) temporarily releases the lru_lock, allowing concurrent progress on the put side without properly removing the glock from the LRU list. This race condition can lead to the glock being accessed after it has been freed, resulting in a use-after-free scenario. Such a flaw can cause kernel memory corruption, potentially leading to system crashes (denial of service) or privilege escalation if exploited by a local attacker. The fix involves ensuring the GLF_LRU flag remains set across the race window opened by cond_resched_lock and only clearing it after the glock is safely removed from the LRU list under the lru_lock. This vulnerability affects multiple versions of the Linux kernel as indicated by the affected commit hashes, and it has been publicly disclosed without known exploits in the wild as of the publication date. No CVSS score has been assigned yet, but the technical details and the nature of the flaw indicate a significant security concern within the kernel's file system locking mechanism.

For European organizations, the impact of CVE-2021-47254 can be substantial, especially for those relying on Linux-based infrastructure, including servers, cloud environments, and embedded systems using GFS2 for clustered file systems. Exploitation of this vulnerability could allow a local attacker to cause denial of service by crashing the kernel or potentially escalate privileges to gain unauthorized root access. This could lead to disruption of critical services, data breaches, or compromise of sensitive information. Organizations operating in sectors with high dependency on Linux servers, such as finance, telecommunications, government, and critical infrastructure, may face increased risk. Additionally, the use of GFS2 in clustered storage environments means that exploitation could affect data availability and integrity across multiple nodes, amplifying the operational impact. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, as attackers may develop exploits following public disclosure. Therefore, European organizations should prioritize patching and monitoring to mitigate potential exploitation.

To mitigate CVE-2021-47254, European organizations should: 1) Apply the official Linux kernel patches that address this use-after-free vulnerability as soon as they become available from trusted sources or Linux distribution vendors. 2) Conduct thorough testing of patched kernels in staging environments to ensure stability and compatibility, particularly in clustered environments using GFS2. 3) Limit local user access on systems running vulnerable kernel versions to trusted personnel only, reducing the attack surface for local exploitation. 4) Implement strict access controls and monitoring on systems with GFS2 to detect unusual behavior or crashes that could indicate exploitation attempts. 5) Maintain up-to-date backups and disaster recovery plans to minimize downtime in case of denial-of-service incidents. 6) Engage in proactive vulnerability management by subscribing to security advisories from Linux kernel maintainers and relevant CERTs to stay informed about updates and emerging threats related to this vulnerability.