CVE-2021-47585 is a memory leak vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically within the __add_inode_ref() function. The vulnerability arises due to improper memory management where allocated memory for the variable victim_name is not freed under certain error conditions. The function allocates memory twice for victim_name using kmalloc(), but in the second allocation scenario (around line 1169), if the call to backref_in_log() returns a negative value (indicating an error), the function returns immediately without freeing the allocated memory. This results in a memory leak. The first allocation scenario correctly frees the memory upon error, but the second does not, leading to inconsistent handling. The memory leak could cause the kernel's memory usage to grow unnecessarily over time, potentially leading to resource exhaustion. Although this vulnerability does not directly allow code execution or privilege escalation, the leak could degrade system stability and availability, especially on systems with heavy Btrfs usage or under repeated error conditions triggering this code path. The vulnerability affects Linux kernel versions identified by the commit hash d3316c8233bb05e0dd855d30aac347bb8ad76ee4 and was publicly disclosed in June 2024. No known exploits are reported in the wild, and no CVSS score has been assigned yet. The fix involves adding a kfree() call to properly release victim_name memory before returning on error in the second allocation path.

For European organizations, the impact of CVE-2021-47585 primarily concerns system stability and availability. Organizations relying on Linux servers with Btrfs filesystems—commonly used for advanced storage features like snapshots and checksumming—may experience gradual memory leaks leading to increased memory consumption. Over time, this can cause system slowdowns, crashes, or forced reboots, disrupting critical services. This is particularly relevant for data centers, cloud providers, and enterprises using Btrfs for storage management. While the vulnerability does not directly compromise confidentiality or integrity, the availability impact can affect business continuity and service reliability. Systems under heavy load or with frequent filesystem operations invoking __add_inode_ref() are at higher risk. Since no authentication or user interaction is required to trigger this leak, any process or kernel operation that encounters the error path can cause the leak, increasing the attack surface. European organizations with large-scale Linux deployments should be aware of this risk, especially in sectors like finance, telecommunications, and government where uptime is critical.

To mitigate CVE-2021-47585, European organizations should prioritize updating their Linux kernel to a version that includes the patch fixing the memory leak in __add_inode_ref(). If immediate patching is not feasible, monitoring system memory usage closely on Btrfs-enabled systems is recommended to detect abnormal growth indicative of leaks. Administrators should audit and limit the use of Btrfs where possible or consider alternative filesystems if stability is paramount and patching is delayed. Additionally, implementing kernel memory leak detection tools and enabling kernel debugging features can help identify and diagnose leaks early. For environments using automated configuration management, integrating kernel updates into regular maintenance cycles will reduce exposure. Finally, organizations should review logs for repeated errors from backref_in_log() calls, as these may signal conditions triggering the leak, allowing proactive intervention.