CVE-2017-18204 in Linux
Summary
by MITRE
The ocfs2_setattr function in fs/ocfs2/file.c in the Linux kernel before 4.14.2 allows local users to cause a denial of service (deadlock) via DIO requests.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2017-18204 resides within the Oracle Cluster File System 2 (OCFS2) implementation in the Linux kernel, specifically within the ocfs2_setattr function located in fs/ocfs2/file.c. This flaw represents a critical denial of service condition that can be exploited by local attackers to induce system-wide deadlock situations. The vulnerability affects Linux kernel versions prior to 4.14.2, making it a significant concern for systems running older kernel releases. The issue manifests when the kernel processes Direct I/O (DIO) requests, which are designed to bypass the kernel's page cache and provide direct access to storage devices. The flaw occurs during attribute modification operations on OCFS2 filesystem files, where the function fails to properly handle concurrent access patterns, leading to a circular wait condition that results in system deadlock.
The technical implementation of this vulnerability stems from improper locking mechanisms within the ocfs2_setattr function. When DIO requests are processed, the function attempts to acquire multiple locks in a specific order while simultaneously handling attribute changes. The flaw arises from a scenario where two or more processes attempt to acquire these locks in different orders, creating a deadlock condition. This type of vulnerability falls under the category of improper locking as classified by CWE-661, where the system fails to properly manage concurrent access to shared resources. The deadlock occurs because the function does not implement proper lock ordering or deadlock detection mechanisms, allowing the system to reach a state where processes are indefinitely waiting for resources held by other processes in the cycle. The vulnerability is particularly dangerous because it can be triggered through normal filesystem operations, making it difficult to prevent through simple access controls or monitoring.
The operational impact of CVE-2017-18204 extends beyond simple denial of service to potentially compromise entire system availability and stability. Local attackers who can execute code on the target system can exploit this vulnerability to cause system-wide lockups, requiring manual intervention or system reboot to restore normal operation. The nature of the deadlock means that the system may become unresponsive to all I/O operations, including critical system functions, effectively rendering the system unusable until the deadlock is resolved. This vulnerability is particularly concerning in enterprise environments where OCFS2 is commonly used for shared storage solutions, as it could affect database servers, file servers, and other mission-critical applications that rely on cluster filesystems. The exploitability of this vulnerability is relatively low compared to remote attacks, as it requires local access, but the potential for system compromise remains high given that local users may have elevated privileges in many environments. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation and denial of service tactics, as it allows local users to cause system instability and potentially gain unauthorized access to system resources through the resulting system state.
Mitigation strategies for CVE-2017-18204 primarily focus on kernel version updates and system hardening measures. The most effective approach involves upgrading to Linux kernel version 4.14.2 or later, where the vulnerability has been addressed through proper lock management and deadlock prevention mechanisms. System administrators should implement regular patch management procedures to ensure all systems are running patched kernel versions. Additionally, monitoring for unusual I/O patterns and system lockup conditions can help detect potential exploitation attempts. The vulnerability highlights the importance of proper lock ordering in kernel space programming and demonstrates the need for comprehensive testing of concurrent access scenarios. Organizations should also consider implementing application-level monitoring to detect filesystem access patterns that might indicate exploitation attempts, particularly in environments where OCFS2 is actively used. Security teams should review their incident response procedures to account for potential deadlock scenarios and ensure appropriate recovery mechanisms are in place for systems running vulnerable kernel versions.