CVE-2015-7891 in Android
Summary
by MITRE
Race condition in the ioctl implementation in the Samsung Graphics 2D driver (aka /dev/fimg2d) in Samsung devices with Android L(5.0/5.1) allows local users to trigger memory errors by leveraging definition of g2d_lock and g2d_unlock lock macros as no-ops, aka SVE-2015-4598.
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Analysis
by VulDB Data Team • 06/09/2024
The vulnerability CVE-2015-7891 represents a critical race condition within the Samsung Graphics 2D driver implementation, specifically affecting Android Lollipop versions 5.0 and 5.1. This flaw exists in the /dev/fimg2d device driver which handles 2D graphics operations on Samsung mobile devices. The vulnerability stems from improper synchronization mechanisms within the ioctl interface, creating a window where concurrent operations can lead to unpredictable memory states and potential system instability. The issue is particularly concerning as it affects the core graphics subsystem that handles numerous user-facing operations including UI rendering, image processing, and multimedia applications. The race condition manifests when multiple processes or threads attempt to access the graphics hardware simultaneously without proper locking mechanisms, leading to potential memory corruption and system crashes.
The technical root cause of this vulnerability lies in the definition of g2d_lock and g2d_unlock macros which are implemented as no-ops, meaning they perform no actual locking operations. This design flaw creates a scenario where the intended synchronization between concurrent graphics operations fails completely, allowing multiple threads to access shared resources simultaneously. When the graphics driver processes multiple ioctl calls in rapid succession, the absence of proper locking means that memory regions can be accessed and modified concurrently, leading to data races and memory corruption. The vulnerability specifically impacts the Samsung Graphics 2D driver's handling of hardware resource allocation and deallocation, where the lack of atomic operations during critical sections enables malicious or accidental interference with ongoing graphics processing operations. This weakness aligns with CWE-362, which describes a race condition vulnerability where two or more threads access shared data concurrently and at least one of the threads is writing to the data, causing unpredictable behavior.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation and arbitrary code execution within the graphics processing context. Local attackers can exploit this race condition to trigger memory errors that may result in system crashes, application hangs, or more severe consequences including the ability to execute code with elevated privileges. The vulnerability affects the integrity of the graphics subsystem and can compromise the overall security posture of the device by providing an attack surface that operates at a low privilege level but can influence critical system operations. Attackers can leverage this flaw to cause denial of service conditions, potentially leading to persistent system instability that affects user experience and device functionality. The nature of the race condition also makes it particularly challenging to detect and exploit consistently, as the timing and specific conditions required for successful exploitation may vary between different device configurations and usage patterns.
Mitigation strategies for CVE-2015-7891 should focus on implementing proper locking mechanisms within the graphics driver's ioctl implementation, specifically addressing the no-op nature of the g2d_lock and g2d_unlock macros. Device manufacturers should ensure that all shared resources accessed through the graphics driver interface are properly synchronized using appropriate mutex or semaphore operations. The fix should involve replacing the current no-op macros with actual locking implementations that prevent concurrent access to critical graphics hardware resources. Additionally, system administrators and device manufacturers should implement proper input validation and bounds checking for ioctl calls to prevent malicious exploitation attempts. The vulnerability demonstrates the importance of proper concurrent programming practices in kernel-level drivers and highlights the need for thorough security testing of device drivers, particularly those handling hardware resources with direct memory access capabilities. This issue also relates to ATT&CK technique T1068, which involves exploiting legitimate credentials and privileges to gain access to system resources, as the race condition could potentially be leveraged to escalate privileges within the graphics processing subsystem.