CVE-2024-35784 is a vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically related to the handling of extent locking during the fiemap ioctl operation. The issue arises because the extent lock is held for the entire duration of the fiemap call, which copies file extent information to user space. During this process, a page fault can occur when copying data to user space, and if the file range is memory-mapped and a write operation (mkwrite) is triggered, it can cause a deadlock due to recursive locking attempts. The deadlock is triggered because the extent lock is not released while waiting for the page fault to resolve, leading to a circular wait condition. The vulnerability was discovered through lockdep annotations and reproduced with a test case, confirming that the existing extent locking mechanism can cause deadlocks under normal code paths. The fix involves reducing the scope of the extent lock during the fiemap operation, holding it only when searching for delayed allocation (delalloc) extents to maintain consistency, but otherwise releasing it to avoid deadlocks. This change ensures that if ordered extents update during the fiemap call, the kernel can still emit correct extent information without risking deadlocks. The vulnerability does not appear to have been exploited in the wild and affects specific Linux kernel versions identified by commit hashes. It is a concurrency and locking issue within the kernel's filesystem code rather than a memory corruption or privilege escalation flaw.

For European organizations, the impact of CVE-2024-35784 primarily concerns system stability and availability rather than direct confidentiality or integrity breaches. Systems running vulnerable Linux kernel versions with Btrfs filesystems could experience deadlocks leading to kernel hangs or unresponsive behavior when applications perform fiemap ioctl calls on memory-mapped files. This can disrupt services relying on Btrfs, including file servers, database systems, and container environments that use this filesystem. Organizations using Btrfs for critical storage or in environments with high concurrency file operations may face increased risk of system downtime or degraded performance. Although no direct data leakage or privilege escalation is indicated, the deadlock could be leveraged by an attacker with local access to cause denial of service (DoS) conditions. This is particularly relevant for multi-tenant environments, cloud providers, and enterprises with Linux-based infrastructure. The lack of known exploits reduces immediate risk, but the potential for DoS and operational disruption necessitates timely patching. European organizations with compliance requirements for system availability and reliability should prioritize mitigation to avoid service interruptions.

To mitigate CVE-2024-35784, European organizations should: 1) Apply the official Linux kernel patches that address the extent locking deadlock in Btrfs as soon as they become available from trusted sources or Linux distributions. 2) If patching immediately is not feasible, consider temporarily avoiding or limiting the use of fiemap ioctl calls on memory-mapped files within Btrfs filesystems, especially in high-concurrency scenarios. 3) Monitor system logs and kernel messages for signs of deadlocks or hangs related to Btrfs operations and implement alerting to detect potential triggering of this vulnerability. 4) For environments using containers or virtual machines, ensure that host kernels are updated to prevent propagation of deadlocks affecting containerized workloads. 5) Conduct thorough testing of kernel updates in staging environments to confirm stability and compatibility with existing workloads. 6) Maintain robust backup and recovery procedures to minimize impact in case of system hangs or crashes. 7) Engage with Linux distribution vendors and security advisories to track patch releases and deployment recommendations specific to Btrfs and kernel versions in use.