CVE-2024-43885 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix double inode unlock for direct IO sync writes
If we do a direct IO sync write, at btrfs_sync_file(), and we need to skip inode logging or we get an error starting a transaction or an error when flushing delalloc, we end up unlocking the inode when we shouldn't under the 'out_release_extents' label, and then unlock it again at btrfs_direct_write().
Fix that by checking if we have to skip inode unlocking under that label.
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified in the linux kernel btrfs filesystem implementation represents a critical double unlock condition that can lead to system instability and potential security implications. This flaw occurs specifically during direct io sync write operations when the btrfs_sync_file() function processes write requests with specific error conditions. The issue manifests when the filesystem needs to skip inode logging, encounters errors during transaction initiation, or experiences failures during delalloc flushing operations. These error scenarios trigger an improper unlocking sequence where the inode gets unlocked once at the 'out_release_extents' label and then again in the btrfs_direct_write() function, creating a double unlock condition that violates fundamental memory safety principles.
The technical nature of this vulnerability stems from inadequate state management within the btrfs filesystem driver's synchronization mechanisms. When direct io sync writes are processed, the kernel maintains complex locking relationships between inode structures and their associated data extents. The flaw occurs because the code path fails to properly track whether an inode unlock operation has already occurred before proceeding to subsequent cleanup routines. This condition directly relates to common software vulnerabilities categorized under CWE-129 and CWE-476 in the Common Weakness Enumeration system, where improper handling of resource release operations leads to undefined behavior and potential memory corruption scenarios.
The operational impact of this vulnerability extends beyond simple system crashes or hangs, as it can potentially enable privilege escalation attacks or data corruption within the filesystem. When an inode is unlocked twice, the kernel's memory management subsystem may attempt to access freed memory locations or manipulate already-released resources, leading to unpredictable behavior that could be exploited by malicious actors. The vulnerability affects systems utilizing btrfs filesystems with direct io sync writes, which are commonly employed in high-performance storage scenarios and database applications where data integrity is paramount. Attackers could potentially leverage this condition to cause denial of service conditions or gain elevated privileges through careful manipulation of concurrent write operations.
Mitigation strategies for this vulnerability should focus on immediate kernel updates from trusted sources as the primary defense mechanism. System administrators should ensure all btrfs filesystem installations receive the patched kernel versions that implement the corrected unlock logic. The fix involves introducing a conditional check before executing inode unlocking operations at the 'out_release_extents' label, ensuring that subsequent unlock operations only occur when necessary. This approach aligns with standard security practices recommended in the ATT&CK framework for operating system kernel hardening and memory safety improvements. Organizations should also implement monitoring solutions to detect anomalous filesystem behavior patterns that might indicate exploitation attempts, while maintaining regular kernel update schedules to address similar vulnerabilities proactively. The vulnerability demonstrates the critical importance of proper resource management in kernel space operations and reinforces the need for comprehensive testing of error handling paths in filesystem drivers.