CVE-2021-47530 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
drm/msm: Fix wait_fence submitqueue leak
We weren't dropping the submitqueue reference in all paths. In particular, when the fence has already been signalled. Split out a helper to simplify handling this in the various different return paths.
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2021-47530 resides within the Linux kernel's graphics subsystem, specifically affecting the display subsystem's msm driver component. This issue represents a memory leak scenario that occurs during the processing of graphics command submissions through the drm/msm framework. The vulnerability manifests when the kernel fails to properly release reference counts on submitqueue objects, creating a resource management inconsistency that can lead to gradual memory exhaustion over time. The msm driver is responsible for managing graphics processing units in Qualcomm-based systems, making this a critical issue for mobile and embedded devices that rely on these graphics implementations. The flaw specifically impacts the handling of fence objects which are used to synchronize graphics command execution between different hardware components and software layers.
The technical implementation of this vulnerability stems from improper reference counting within the graphics command submission pipeline. When a fence object has already been signaled, indicating that a graphics command has completed execution, the kernel should release its reference to the associated submitqueue object. However, the code path fails to execute this cleanup operation in all possible execution scenarios, particularly when the fence is already in a signaled state. This creates a situation where the submitqueue reference count remains elevated indefinitely, preventing the kernel from properly reclaiming the associated memory resources. The vulnerability is classified as a resource leak under CWE-404, which specifically addresses improper resource management and memory leaks in software systems. The reference counting mechanism that should automatically clean up unused resources becomes corrupted due to the missing reference drop in certain code paths.
The operational impact of this vulnerability extends beyond simple memory consumption issues, potentially affecting system stability and performance over extended periods of graphics usage. As the memory leak accumulates, system resources become increasingly constrained, which can lead to application crashes, system slowdowns, or in extreme cases, complete system instability. The vulnerability is particularly concerning in mobile environments where system resources are already constrained and where graphics-intensive applications are common. Attackers could potentially exploit this memory leak to cause denial of service conditions by repeatedly submitting graphics commands that trigger the faulty code path, leading to progressive system degradation. The vulnerability affects all systems running Linux kernels with the drm/msm driver enabled, particularly those using Qualcomm Snapdragon processors or similar graphics architectures. This aligns with ATT&CK technique T1499.001 for resource exhaustion attacks, where adversaries leverage memory leaks to consume system resources and cause service disruption.
Mitigation strategies for CVE-2021-47530 primarily involve updating to kernel versions that contain the patched implementation. The fix implemented by the Linux kernel developers involves creating a dedicated helper function to ensure consistent reference dropping across all execution paths, particularly when dealing with already-signaled fence objects. This approach addresses the root cause by centralizing the reference management logic and ensuring that all code paths properly handle the cleanup operations. System administrators should prioritize applying kernel updates that include this fix, especially in production environments where graphics-intensive workloads are common. Additionally, monitoring systems for unusual memory consumption patterns can help detect potential exploitation attempts. The fix demonstrates proper defensive programming practices by ensuring that resource cleanup occurs regardless of execution flow, which aligns with secure coding guidelines and helps prevent similar issues in other kernel subsystems. Organizations should also implement automated patch management processes to ensure timely deployment of security fixes across all affected systems.