CVE-2016-6130 in Linux
Summary
by MITRE
Race condition in the sclp_ctl_ioctl_sccb function in drivers/s390/char/sclp_ctl.c in the Linux kernel before 4.6 allows local users to obtain sensitive information from kernel memory by changing a certain length value, aka a "double fetch" vulnerability.
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Analysis
by VulDB Data Team • 08/26/2022
The CVE-2016-6130 vulnerability represents a critical race condition flaw within the Linux kernel's s390 architecture subsystem, specifically affecting the sclp_ctl_ioctl_sccb function in the drivers/s390/char/sclp_ctl.c file. This vulnerability exists in kernel versions prior to 4.6 and constitutes a classic double fetch vulnerability that enables local attackers to extract sensitive kernel memory information. The flaw manifests when an attacker manipulates a specific length value during ioctl operations, creating a temporal window where the system's memory state can be exploited to disclose confidential data. The s390 architecture, which is primarily used in IBM mainframe systems, employs the Service Call Logical Processor (SCLP) for communication between the operating system and hardware, making this vulnerability particularly concerning for enterprise environments relying on these systems.
The technical implementation of this vulnerability stems from improper input validation and synchronization mechanisms within the ioctl handling code. During the execution of the sclp_ctl_ioctl_sccb function, the kernel performs a fetch operation to determine buffer size, then later fetches the same data again for processing. However, between these two fetch operations, an attacker can modify the length parameter, causing the second fetch to reference different memory locations than the first. This temporal inconsistency creates a window where kernel memory contents can be inadvertently exposed through the ioctl interface. The vulnerability falls under the CWE-362 category of Race Conditions, specifically manifesting as a double fetch scenario where the same data is accessed twice with potentially different values. This type of vulnerability is particularly dangerous because it can be exploited to reveal kernel pointers, stack contents, or other sensitive information that could aid in further exploitation attempts.
The operational impact of CVE-2016-6130 extends beyond simple information disclosure, as it provides attackers with potential leverage for more sophisticated attacks within the kernel space. Local users who can access the affected ioctl interface can use this vulnerability to gain insights into kernel memory layout, which is invaluable for developing exploits targeting other vulnerabilities. The exposure of kernel memory contents can reveal stack canaries, kernel pointers, and other security-sensitive data that would otherwise remain protected. This information disclosure can be particularly damaging in enterprise environments where IBM mainframe systems are deployed, as it provides attackers with the knowledge necessary to bypass kernel security mechanisms. The vulnerability also aligns with ATT&CK technique T1059.001 for executing malicious code through kernel interfaces and T1068 for local privilege escalation by leveraging kernel memory exposure to craft more effective attacks.
Mitigation strategies for CVE-2016-6130 primarily focus on kernel version updates, as the vulnerability was addressed in kernel version 4.6 through proper synchronization mechanisms and input validation. Organizations should prioritize immediate deployment of kernel updates to patch this vulnerability, especially in environments where IBM mainframe systems operate with Linux kernel components. Additionally, implementing proper access controls and limiting local user privileges can reduce the attack surface, though this does not eliminate the vulnerability entirely. System administrators should also monitor for unusual ioctl activity patterns that might indicate exploitation attempts, as the vulnerability requires specific conditions to be met for successful exploitation. The fix implemented in kernel 4.6 involved strengthening the synchronization mechanisms within the ioctl handling code and ensuring that buffer size parameters are validated consistently throughout the execution flow, preventing the temporal inconsistencies that enabled the double fetch attack pattern.