CVE-2016-9120 in Linux
Summary
by MITRE • 01/25/2023
Race condition in the ion_ioctl function in drivers/staging/android/ion/ion.c in the Linux kernel before 4.6 allows local users to gain privileges or cause a denial of service (use-after-free) by calling ION_IOC_FREE on two CPUs at the same time.
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Analysis
by VulDB Data Team • 08/10/2025
The vulnerability described in CVE-2016-9120 represents a critical race condition within the Linux kernel's Android ION memory management subsystem. This flaw exists in the ion_ioctl function located in drivers/staging/android/ion/ion.c and affects kernel versions prior to 4.6. The ION subsystem provides an interface for managing memory allocations in Android devices, particularly for graphics and multimedia applications. The race condition occurs when multiple CPU cores attempt to execute the ION_IOC_FREE ioctl command simultaneously, creating a scenario where memory management operations can interfere with each other during concurrent execution.
The technical implementation of this vulnerability stems from insufficient synchronization mechanisms within the ion_ioctl function. When two processes or threads invoke ION_IOC_FREE on the same memory handle concurrently, the kernel fails to properly serialize these operations. This lack of proper locking allows one thread to free a memory buffer while another thread is still accessing it, resulting in a use-after-free condition. The race condition specifically manifests when the kernel attempts to manage reference counting and memory deallocation without adequate atomic operations or mutex locks to prevent concurrent access to shared data structures. This flaw falls under the CWE-362 category of "Concurrent Execution using Shared Resource with Improper Synchronization" and aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation" through kernel-level vulnerabilities.
The operational impact of this vulnerability is significant and multifaceted. Local attackers can exploit this race condition to achieve privilege escalation, potentially gaining root access to the system, or to cause a denial of service through system crashes. The use-after-free condition can lead to memory corruption that may be leveraged to execute arbitrary code with elevated privileges. Additionally, the concurrent nature of the vulnerability means that legitimate system operations could be disrupted, causing instability and potential system hangs. The vulnerability affects Android devices and Linux systems that utilize the ION memory management subsystem, making it particularly relevant for mobile platforms and embedded systems.
Mitigation strategies for this vulnerability involve applying the kernel patch released with version 4.6, which implements proper synchronization mechanisms to prevent concurrent access to memory management operations. System administrators should prioritize updating to kernel versions that contain the fix, as the vulnerability can be exploited by any local user with access to the system. Organizations should also implement monitoring for unusual system behavior that might indicate exploitation attempts, such as unexpected kernel crashes or memory allocation failures. The fix typically involves adding appropriate mutex locks or other synchronization primitives around the critical sections of code where memory deallocation occurs. Security teams should also consider implementing additional controls such as kernel hardening measures and access controls to limit the potential impact of any exploitation attempts, while the vulnerability itself demonstrates the importance of proper concurrent programming practices in kernel space operations.