CVE-2017-14340 in Linux
Summary
by MITRE
The XFS_IS_REALTIME_INODE macro in fs/xfs/xfs_linux.h in the Linux kernel before 4.13.2 does not verify that a filesystem has a realtime device, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) via vectors related to setting an RHINHERIT flag on a directory.
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Analysis
by VulDB Data Team • 12/29/2022
The vulnerability described in CVE-2017-14340 represents a critical flaw in the Linux kernel's XFS filesystem implementation that enables local privilege escalation and system instability. This issue affects Linux kernel versions prior to 4.13.2 and stems from a fundamental design oversight in the XFS_IS_REALTIME_INODE macro located within the fs/xfs/xfs_linux.h file. The flaw specifically manifests when the kernel fails to properly validate whether a filesystem actually possesses a realtime device before attempting operations on it, creating a dangerous condition that can be exploited by local users to trigger system crashes.
The technical nature of this vulnerability resides in the improper validation mechanism within the XFS subsystem where the XFS_IS_REALTIME_INODE macro does not perform adequate checks to confirm that a filesystem has an associated realtime device. When local users manipulate filesystem attributes by setting the RHINHERIT flag on directories, the kernel attempts to access memory locations that may not be properly initialized or allocated. This leads to a NULL pointer dereference condition that results in an OOPS message and subsequent system crash, effectively causing a denial of service condition that can bring the entire system to a halt.
The operational impact of this vulnerability extends beyond simple system instability, as it provides a pathway for local attackers to disrupt system operations and potentially exploit other related weaknesses in the kernel's memory management subsystem. The flaw is particularly concerning because it can be triggered through legitimate filesystem operations that users might perform during normal system usage, making detection difficult and increasing the attack surface. From an attacker's perspective, this vulnerability allows for reliable denial of service attacks that can be executed with minimal privileges, making it an attractive target for malicious actors seeking to disrupt system availability.
The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and it maps to several ATT&CK techniques including privilege escalation and denial of service through kernel exploitation. This weakness specifically enables an attacker to leverage local filesystem operations to achieve system instability, potentially leading to more severe consequences when combined with other kernel vulnerabilities. The flaw demonstrates poor input validation and insufficient boundary checking within the kernel's XFS implementation, representing a classic example of how inadequate defensive programming can create exploitable conditions in critical system components.
Mitigation strategies for this vulnerability require immediate kernel updates to version 4.13.2 or later, where the XFS_IS_REALTIME_INODE macro has been properly enhanced to validate filesystem configurations before proceeding with operations. System administrators should also implement monitoring solutions to detect unusual filesystem attribute changes that might indicate exploitation attempts, particularly around directory operations and RHINHERIT flag manipulations. Additionally, organizations should consider implementing kernel lockdown mechanisms and restricting local user privileges where possible to minimize the potential impact of such vulnerabilities. The fix implemented in the updated kernel versions ensures proper validation of filesystem device configurations before any operations are performed, preventing the NULL pointer dereference condition that previously enabled this denial of service attack vector.