CVE-2024-56780 is a vulnerability identified in the Linux kernel related to the quota subsystem's handling of workqueue flushing during filesystem freeze operations. Specifically, the issue arises in the quota writeback mechanism, which is responsible for writing back disk quota information to persistent storage. The vulnerability occurs because the quota_release_work workqueue is not always flushed during the quota writeback process, particularly when the filesystem is frozen (e.g., during freeze_super() calls). This leads to a race condition where dquot structures (disk quota objects) are added to a releasing list but the workqueue flushing is deferred until after the filesystem freeze completes. When the kernel eventually attempts to flush the workqueue while the filesystem is still frozen, it triggers a WARN_ON condition due to an attempt to start a journal transaction on a frozen filesystem. This results in kernel warnings and dmesg log noise, potentially causing system instability or failures in filesystem operations. The problem was observed on a PowerPC machine with 15 cores, indicating it may affect multi-core systems under certain workloads. The fix involves ensuring that the quota_release_work workqueue is flushed during the dquot_writeback_dquots() call, preventing any pending work items from remaining after the filesystem freeze. This correction avoids the race condition and the associated kernel warnings. The vulnerability affects multiple Linux kernel versions identified by specific git commit hashes, indicating it is present in several recent kernel builds prior to the patch. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, this vulnerability primarily impacts systems running affected Linux kernel versions with quota management enabled, especially those using the ext4 filesystem or similar that rely on quota writeback mechanisms. The issue can cause kernel warnings and potentially destabilize systems during filesystem freeze operations, which are often used in backup, snapshot, or maintenance scenarios. This can lead to unexpected system behavior, degraded performance, or even service interruptions if critical filesystems become unstable or fail to synchronize properly. Organizations with large-scale Linux deployments, such as cloud providers, data centers, and enterprises relying on Linux-based infrastructure, may experience operational disruptions. While the vulnerability does not directly lead to privilege escalation or remote code execution, the resulting instability could be exploited indirectly by attackers to cause denial of service or complicate forensic investigations. Given the widespread use of Linux in European public sector, financial institutions, and technology companies, the impact could be significant if unpatched systems are subjected to workloads triggering this race condition.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernels to versions that include the patch ensuring the quota_release_work workqueue is flushed during dquot_writeback_dquots(). Kernel updates should be tested and deployed promptly, especially on systems with quota management enabled and ext4 filesystems. Additionally, administrators should audit their systems to identify affected kernel versions and verify if quota writeback and filesystem freeze operations are in use. Where immediate patching is not feasible, operational mitigations include avoiding filesystem freeze operations during high quota activity or scheduling maintenance windows to minimize the risk of triggering the race condition. Monitoring kernel logs (dmesg) for WARN_ON messages related to ext4_journal_check_start or quota_release_workfn can help detect attempts to exploit or encounter the issue. Finally, organizations should ensure robust backup and recovery procedures are in place to recover from potential filesystem inconsistencies caused by this vulnerability.