CVE-2017-18224 in Linux
Summary
by MITRE
In the Linux kernel before 4.15, fs/ocfs2/aops.c omits use of a semaphore and consequently has a race condition for access to the extent tree during read operations in DIRECT mode, which allows local users to cause a denial of service (BUG) by modifying a certain e_cpos field.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2017-18224 represents a critical race condition flaw within the Linux kernel's OCFS2 (Oracle Cluster File System 2) implementation that affects versions prior to 4.15. This issue specifically resides in the fs/ocfs2/aops.c file where the kernel fails to properly utilize a semaphore mechanism during direct mode read operations. The omission of proper synchronization creates a scenario where multiple concurrent processes can simultaneously access and modify the extent tree data structure without adequate protection, leading to unpredictable system behavior and potential system crashes.
The technical root cause of this vulnerability stems from the absence of proper locking mechanisms when handling extent tree modifications during direct I/O operations in the OCFS2 filesystem. When a file is accessed in direct mode, the kernel must maintain consistency of the extent tree structure that maps logical file blocks to physical storage locations. The missing semaphore protection allows concurrent threads to interfere with each other's operations on the e_cpos field, which represents the starting position of an extent within the file. This race condition can result in corrupted data structures and ultimately trigger kernel BUG messages that force system instability and require manual intervention.
From an operational perspective, this vulnerability poses significant risks to systems utilizing OCFS2 filesystems, particularly in clustered environments where multiple nodes access shared storage. Local users with appropriate privileges can exploit this flaw to induce denial of service conditions by carefully manipulating the extent tree structure during read operations. The impact extends beyond simple service disruption as the kernel BUG messages indicate deeper structural corruption that may require system rebooting and data recovery procedures. The vulnerability is particularly concerning in enterprise environments where OCFS2 is commonly deployed for high-availability applications and database storage solutions.
The vulnerability aligns with CWE-362, which specifically addresses race conditions in concurrent programming, and demonstrates how improper synchronization mechanisms can lead to system instability. From an ATT&CK framework perspective, this represents a privilege escalation vector through local code execution that can result in system compromise and denial of service. Organizations should prioritize applying the kernel patch released with version 4.15 to address this vulnerability, as the fix implements proper semaphore usage to protect access to the extent tree during concurrent read operations. Additionally, system administrators should monitor for unusual kernel BUG messages and implement proper access controls to limit local user privileges that could exploit this condition. The remediation process requires careful consideration of system downtime and backup procedures, particularly in clustered environments where coordinated updates across multiple nodes may be necessary to ensure complete protection against this race condition vulnerability.