CVE-2021-47234 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
phy: phy-mtk-tphy: Fix some resource leaks in mtk_phy_init()
Use clk_disable_unprepare() in the error path of mtk_phy_init() to fix some resource leaks.
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Analysis
by VulDB Data Team • 08/06/2025
The vulnerability identified as CVE-2021-47234 resides within the Linux kernel's phy-mtk-tphy driver, specifically affecting MediaTek USB Type-C PHY controllers. This issue represents a resource management flaw that occurs during the initialization process of USB PHY hardware interfaces. The problem manifests when the mtk_phy_init() function encounters errors during hardware initialization, failing to properly release allocated resources. The root cause stems from inadequate error handling in the driver's resource cleanup paths, which directly violates established kernel programming practices and security principles.
The technical flaw involves the improper handling of clock resources within the MediaTek USB Type-C PHY driver. When mtk_phy_init() encounters initialization failures, it should invoke clk_disable_unprepare() to ensure that clock resources are properly released back to the system. However, the original implementation omitted this cleanup call in error paths, leading to clock resource leaks that persist even after initialization failures. This behavior creates a denial of service condition where system resources become unavailable for subsequent operations, as the leaked clock resources remain allocated and unusable. The vulnerability aligns with CWE-404, which addresses improper resource release or cleanup, and demonstrates a classic example of resource leak in kernel space code.
The operational impact of this vulnerability extends beyond simple resource waste, potentially affecting system stability and performance in embedded devices running Linux kernels. Mobile devices, tablets, and other hardware platforms utilizing MediaTek USB controllers may experience degraded performance or unexpected system behavior when the PHY initialization fails and resources remain allocated. The resource leaks could compound over time, especially in systems with frequent USB interface initialization attempts, leading to progressive resource exhaustion. This vulnerability particularly affects devices where USB connectivity is critical for normal operation, as persistent resource leaks could prevent proper USB functionality and system recovery. The issue represents a significant concern for device manufacturers and system integrators who rely on stable kernel behavior for their embedded solutions.
Mitigation strategies for CVE-2021-47234 involve applying the kernel patch that ensures clk_disable_unprepare() is called in all error paths of the mtk_phy_init() function. System administrators and device manufacturers should prioritize updating to kernel versions containing this fix, typically found in kernel releases 5.13 and later. The patch implementation directly addresses the root cause by ensuring proper resource cleanup regardless of initialization success or failure. Organizations should also implement comprehensive testing procedures to verify that USB PHY initialization behaves correctly under various error conditions. Additionally, monitoring system resource usage and implementing automated alerting for resource exhaustion conditions can help detect potential exploitation of similar vulnerabilities. This fix aligns with ATT&CK technique T1499.004, which covers resource exhaustion, and demonstrates the importance of proper error handling in kernel drivers to maintain system integrity and availability.