CVE-2024-42111 is a vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically within the btrfs_qgroup_inherit function. The issue arises due to improper validation checks on the btrfs_qgroup_inherit structure when quota groups (qgroups) are enabled or disabled concurrently. A recent commit (b5357cb268c4) intended to optimize qgroup inheritance checks by skipping them entirely if qgroups were disabled inadvertently bypassed essential basic validation checks such as num_ref_copies, num_excl_copies, and structure size verification. This creates a race condition where if a btrfs_qgroup_inherit structure is passed while qgroups are disabled, the checks are skipped. Later, when the transaction commits and qgroups are re-enabled, the kernel uses this unchecked, potentially malformed structure, leading to a slab-out-of-bounds read detected by Kernel Address Sanitizer (KASAN). This can cause kernel crashes or memory corruption. The fix involves modifying the btrfs_qgroup_check_inherit function to only skip source qgroup checks while still performing fundamental validations regardless of qgroup state, ensuring invalid structures are rejected and maintaining kernel stability and security. This vulnerability is rooted in concurrency and validation logic flaws within the Btrfs quota group subsystem and affects Linux kernel versions containing the specified commits.

For European organizations relying on Linux systems with Btrfs filesystems, this vulnerability poses a risk of local privilege escalation or denial of service through kernel crashes or memory corruption. Since Btrfs is commonly used in enterprise Linux distributions and cloud environments, exploitation could disrupt critical services, cause data loss, or enable attackers with local access to destabilize systems. The race condition nature means exploitation requires precise timing or specific workloads, limiting remote exploitation but increasing risk in multi-tenant or shared environments such as cloud providers or data centers prevalent in Europe. Disruption of storage subsystems could impact availability of services, especially for organizations using Btrfs snapshots and quota groups for data management. While no known exploits are reported in the wild, the vulnerability's presence in the Linux kernel—a core component in European infrastructure—means that timely patching is essential to prevent potential attacks that could compromise confidentiality, integrity, or availability of systems.

European organizations should prioritize updating Linux kernels to versions that include the fix for CVE-2024-42111. Specifically, ensure that kernel versions incorporate the patch that modifies btrfs_qgroup_check_inherit to enforce basic validation regardless of qgroup state. For environments where immediate patching is not feasible, consider disabling Btrfs quota groups if not in use, to reduce attack surface. Implement strict access controls to limit local user permissions, as exploitation requires local code execution. Employ kernel hardening techniques such as KASAN or other memory safety tools in development and testing environments to detect similar issues early. Monitor system logs for kernel warnings or crashes related to Btrfs qgroup operations. In cloud or multi-tenant setups, isolate workloads and restrict untrusted users from performing Btrfs snapshot or quota operations. Finally, maintain a robust patch management process to rapidly deploy kernel updates across all Linux systems.