CVE-2018-5845 in Android
Summary
by MITRE
A race condition in drm_atomic_nonblocking_commit() in the display driver can potentially lead to a Use After Free scenario in all Android releases from CAF (Android for MSM, Firefox OS for MSM, QRD Android) using the Linux Kernel.
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Analysis
by VulDB Data Team • 02/15/2020
The vulnerability identified as CVE-2018-5845 represents a critical race condition within the drm_atomic_nonblocking_commit() function of Android's display driver subsystem. This flaw exists within the Linux kernel implementation used across various Android variants including CAF (Android for MSM), Firefox OS for MSM, and QRD Android platforms. The race condition manifests during atomic commit operations in display subsystems where multiple threads or processes attempt to access shared memory resources simultaneously without proper synchronization mechanisms. The vulnerability specifically affects Android releases that utilize the Linux kernel's display subsystem for managing graphics rendering and display output operations.
The technical exploitation of this vulnerability leads to a Use After Free condition, which occurs when memory that has been deallocated is still accessed by subsequent operations within the display driver's atomic commit path. This race condition typically arises when one thread frees a memory structure while another thread simultaneously attempts to access the same structure, creating a scenario where the freed memory gets reallocated to a different purpose. The drm_atomic_nonblocking_commit() function handles display state transitions in atomic modesetting operations, where display configuration changes are applied atomically to prevent visual artifacts. When concurrent access occurs during this process, the kernel's memory management subsystem fails to properly coordinate the allocation and deallocation of display state structures, resulting in the corrupted memory access pattern that characterizes the use after free vulnerability.
The operational impact of CVE-2018-5845 extends beyond simple system instability, as it can potentially enable arbitrary code execution within the kernel context. Attackers who can trigger the race condition may leverage this vulnerability to escalate privileges from user-space applications to kernel-level operations, effectively gaining complete system control. This represents a severe security risk for mobile devices running affected Android versions, as it could allow malicious applications to bypass security boundaries and execute privileged operations. The vulnerability affects all Android releases using the Linux kernel's display driver subsystem, making it particularly widespread across the mobile ecosystem. The use of the Linux kernel's display subsystem in these platforms creates a common attack surface that impacts numerous device manufacturers and their respective software implementations.
Mitigation strategies for CVE-2018-5845 focus on implementing proper synchronization mechanisms within the drm_atomic_nonblocking_commit() function to prevent concurrent access to shared memory structures. The recommended approach involves adding appropriate locking mechanisms such as mutexes or spinlocks around critical sections where display state modifications occur. Additionally, developers should ensure that all memory management operations within the atomic commit path properly handle reference counting and synchronization between concurrent threads. The fix typically requires modifications to the kernel's display driver code to ensure that memory structures are not freed until all references to them have been properly released. Organizations should prioritize updating their Android implementations to versions that include patches addressing this race condition, as the vulnerability represents a significant risk to device security and stability. The mitigation efforts align with common security practices outlined in CWE-362 (Concurrent Execution using Shared Resource with Unprotected Critical Section) and may involve techniques from ATT&CK framework's privilege escalation tactics. This vulnerability highlights the importance of proper synchronization in kernel-level code and demonstrates how seemingly minor race conditions can result in severe security implications when operating in security-sensitive contexts.