CVE-2024-46751 in Linux
Summary
by MITRE • 09/18/2024
In the Linux kernel, the following vulnerability has been resolved:
btrfs: don't BUG_ON() when 0 reference count at btrfs_lookup_extent_info()
Instead of doing a BUG_ON() handle the error by returning -EUCLEAN, aborting the transaction and logging an error message.
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Analysis
by VulDB Data Team • 04/05/2026
The vulnerability identified as CVE-2024-46751 affects the Linux kernel's btrfs file system implementation and represents a critical issue in error handling mechanisms. This flaw exists within the btrfs_lookup_extent_info() function where the kernel previously employed a BUG_ON() macro to terminate execution when encountering a zero reference count condition. The BUG_ON() macro is designed to trigger kernel oops and system crashes when certain assumptions fail, making it inappropriate for recoverable error conditions. This approach fundamentally violates proper error handling principles and creates a potential denial of service scenario where legitimate system operations can cause kernel panics and complete system instability.
The technical flaw stems from an improper error handling strategy within the btrfs file system's extent information lookup mechanism. When btrfs_lookup_extent_info() encounters a zero reference count, which can occur during normal file system operations due to concurrent access patterns or race conditions, the kernel's response should be graceful error recovery rather than immediate system termination. The original implementation used BUG_ON() which is defined in the Linux kernel's kernel.h header file and is intended for unrecoverable programming errors where the kernel's assumptions have been violated. This is a violation of the CWE-754 standard for improper check for unusual conditions, as the condition is not truly exceptional but rather a legitimate state that should be handled gracefully.
From an operational impact perspective, this vulnerability poses significant risks to systems relying on btrfs file systems, particularly in enterprise environments where system stability and uptime are critical. The improper handling of zero reference counts can lead to unexpected system crashes, requiring manual intervention and potentially causing data loss or service disruption. The vulnerability affects any system running a Linux kernel version containing the affected btrfs implementation and can be triggered through normal file system operations involving extent management. This makes it particularly dangerous as it doesn't require special privileges or malicious input to exploit, making it a latent threat that can manifest during routine system operations.
The recommended mitigation strategy involves updating to a patched kernel version that implements proper error handling by returning -EUCLEAN instead of triggering BUG_ON(). This change aligns with the ATT&CK framework's concept of privilege escalation through kernel exploits and represents a fundamental improvement in system resilience. The fix ensures that when a zero reference count is encountered, the system logs an appropriate error message, aborts the current transaction, and allows the file system to remain operational rather than crashing the entire kernel. This approach follows the principle of fail-safe design and aligns with industry standards for robust kernel development practices. Organizations should prioritize applying this patch as it addresses a core kernel stability issue that could be exploited to cause denial of service attacks against systems using btrfs file systems. The solution demonstrates proper error handling methodology by using appropriate return codes and transaction management rather than abrupt system termination, thereby maintaining system integrity and availability.