CVE-2024-56758 is a vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically within the function relocate_one_folio(). The issue arises due to a race condition involving folio locking and mapping validation during concurrent operations. When btrfs_read_folio() is called to update a folio, it unlocks the folio before reacquiring the lock. This unlock allows other threads to modify or invalidate the folio's mapping concurrently. If a thread modifies the mapping (such as removing it via invalidate_inode_pages2()) before the folio_lock() is reacquired, subsequent operations assume the mapping is valid when it is actually NULL. This leads to a NULL pointer dereference and kernel crash, as demonstrated by the provided kernel oops trace. The race condition is particularly triggered when relocating data extents concurrently with aborting a transaction, where cleanup_one_transaction() calls destroy_delalloc_inodes(), which in turn invalidates inode pages and sets the mapping to NULL while holding the folio_lock. The vulnerable code fails to verify the mapping's validity after reacquiring the lock, resulting in a crash in set_page_extent_mapped(). This vulnerability stems from a long-standing race condition introduced in 2009 but only recently causing practical crashes due to code changes. The flaw affects multiple Linux kernel versions identified by specific commit hashes. No known exploits are reported in the wild, and no CVSS score has been assigned yet. The vulnerability impacts system stability and availability by causing kernel panics and crashes during filesystem operations on Btrfs volumes.

For European organizations relying on Linux systems with Btrfs filesystems, this vulnerability poses a risk of system crashes and unplanned downtime. Critical infrastructure, cloud service providers, and enterprises using Btrfs for storage management could experience kernel panics leading to service interruptions. This can affect data availability and operational continuity, especially in environments with high concurrency and frequent filesystem transactions. Although the vulnerability does not directly expose confidentiality or integrity risks, the denial-of-service impact can disrupt business operations and potentially lead to data loss if crashes occur during critical write operations. Organizations with automated transaction aborts or heavy filesystem relocation workloads are at higher risk. The lack of known exploits reduces immediate threat but does not eliminate the risk of future weaponization. European entities with compliance requirements for system availability and reliability must prioritize addressing this issue to maintain operational resilience.

Organizations should promptly apply the official Linux kernel patches that address this race condition in the Btrfs codebase. Since the vulnerability involves kernel-level code, updating to a patched kernel version is the most effective mitigation. For environments where immediate patching is challenging, consider temporarily avoiding heavy concurrent Btrfs relocation and transaction abort operations to reduce exposure. Monitoring kernel logs for signs of NULL pointer dereferences or oops events related to Btrfs can help detect exploitation attempts or crashes. Additionally, implementing robust backup and recovery procedures will mitigate the impact of potential data loss from crashes. System administrators should also audit and limit concurrent filesystem operations that trigger the race condition. Employing kernel live patching solutions where available can reduce downtime during patch deployment. Finally, maintain awareness of updates from Linux kernel maintainers and security advisories to respond swiftly to any emerging exploit reports.