CVE-2016-6156 in Linux
Summary
by MITRE
Race condition in the ec_device_ioctl_xcmd function in drivers/platform/chrome/cros_ec_dev.c in the Linux kernel before 4.7 allows local users to cause a denial of service (out-of-bounds array access) by changing a certain size value, aka a "double fetch" vulnerability.
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Analysis
by VulDB Data Team • 09/13/2022
The vulnerability identified as CVE-2016-6156 represents a critical race condition flaw within the Linux kernel's ChromeOS EC device driver implementation. This issue resides in the ec_device_ioctl_xcmd function located in drivers/platform/chrome/cros_ec_dev.c and affects kernel versions prior to 4.7. The vulnerability stems from improper handling of data validation during ioctl command processing, creating a scenario where concurrent operations can lead to inconsistent state conditions. The flaw manifests when local users manipulate specific size parameters during device communication, ultimately enabling them to trigger out-of-bounds array access conditions that can result in system instability and denial of service.
The technical nature of this vulnerability aligns with CWE-362, which describes a race condition error where two or more threads or processes access shared data concurrently, leading to unpredictable behavior. This particular implementation follows a "double fetch" pattern where the same data is retrieved twice from potentially inconsistent sources, with the first fetch value being used for validation while the second fetch value is used for actual processing. The kernel's ChromeOS EC device driver fails to maintain consistent state between these two data fetch operations, creating a window where external manipulation can cause the system to process invalid array indices.
The operational impact of CVE-2016-6156 extends beyond simple denial of service to potentially compromise system stability and availability in environments where ChromeOS devices are deployed. Local attackers with minimal privileges can exploit this vulnerability to cause kernel panics, system crashes, or complete service outages by carefully timing their manipulation of size parameters during ioctl operations. The vulnerability is particularly concerning in enterprise environments where ChromeOS devices serve as primary endpoints, as it can be leveraged to disrupt business operations. Additionally, the out-of-bounds array access condition could potentially be chained with other vulnerabilities to escalate privileges or achieve arbitrary code execution, though the direct exploitation path appears to be primarily focused on denial of service.
Mitigation strategies for this vulnerability primarily involve upgrading to Linux kernel version 4.7 or later, where the race condition has been addressed through proper synchronization mechanisms and data validation. System administrators should prioritize patching affected systems and implementing monitoring to detect potential exploitation attempts. The fix typically involves adding proper locking mechanisms around the critical data access points and ensuring that validation occurs only once with consistent data sources. Organizations should also consider implementing runtime protections such as kernel address space layout randomization and stack canaries to further reduce the attack surface. Security teams should monitor for any potential indirect exploitation vectors that might arise from this vulnerability and maintain updated threat intelligence on related attack patterns in the ChromeOS ecosystem. This vulnerability demonstrates the importance of proper concurrent access control in kernel space operations and highlights the need for comprehensive testing of race condition scenarios in device driver implementations.