CVE-2021-47037 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
ASoC: q6afe-clocks: fix reprobing of the driver
Q6afe-clocks driver can get reprobed. For example if the APR services are restarted after the firmware crash. However currently Q6afe-clocks driver will oops because hw.init will get cleared during first _probe call. Rewrite the driver to fill the clock data at runtime rather than using big static array of clocks.
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Analysis
by VulDB Data Team • 01/09/2025
The vulnerability identified as CVE-2021-47037 affects the Linux kernel's Advanced SoC (ASoC) subsystem, specifically within the q6afe-clocks driver component. This driver manages clock resources for Qualcomm's Audio Front End (AFE) subsystem which is integral to audio processing capabilities in mobile and embedded devices. The issue manifests when the Audio Front End driver undergoes re-probing operations, typically occurring during system recovery scenarios such as when APR (Audio Processing Router) services restart following a firmware crash event. The vulnerability represents a critical reliability concern that can lead to system instability and potential audio service disruption.
The technical flaw stems from the driver's implementation approach using a large static array of clock definitions that are populated during the initial probe phase. When the q6afe-clocks driver experiences a re-probe operation, the hardware initialization structure's hw.init field gets cleared during the first probe call, leaving the driver in an inconsistent state. This design pattern fails to account for dynamic reinitialization scenarios that are common in production environments where system services may restart or recover from failures. The static array approach becomes problematic because it does not support runtime modification of clock configurations, which is essential for handling service restarts and recovery operations. This implementation pattern directly violates the principle of robust driver design that must accommodate dynamic system states and recovery scenarios.
The operational impact of this vulnerability extends beyond simple system crashes, affecting the overall reliability and user experience of audio services on affected devices. When the driver encounters a re-probe scenario, the kernel oops (kernel panic) occurs due to accessing freed or uninitialized memory structures, resulting in system instability. This vulnerability particularly affects mobile devices and embedded systems that rely on Qualcomm's AFE subsystem for audio processing, potentially causing complete system lockups or audio service failures that require manual intervention or device reboot. The issue is especially concerning in environments where firmware updates or service restarts are frequent, as these scenarios can trigger the vulnerable code path repeatedly. From an attacker perspective, this represents a denial-of-service vector that can be exploited to destabilize audio services or potentially trigger broader system instability, making it a significant concern for embedded system security and reliability.
The mitigation strategy involves rewriting the q6afe-clocks driver to eliminate the dependency on static clock arrays and instead implement runtime population of clock data structures. This approach ensures that clock information is dynamically constructed during each probe operation, allowing the driver to properly handle re-probe scenarios without losing critical initialization state. The solution aligns with the principle of defensive programming and follows established best practices for kernel driver development. The fix should implement proper initialization and cleanup procedures that can be safely executed multiple times without leaving the driver in an inconsistent state, thereby preventing the kernel oops condition. This remediation addresses the underlying design flaw that violates the principle of robustness in kernel subsystems and ensures that the driver can gracefully handle service restarts and recovery operations. The implementation should follow the CWE-691 principle of ensuring that software components can operate correctly under all expected conditions, including restart and recovery scenarios.
The vulnerability demonstrates a classic example of poor resource management in kernel drivers and aligns with ATT&CK technique T1489 which involves disrupting services to gain access to systems. In enterprise environments, this could potentially be leveraged to create persistent denial-of-service conditions that affect audio services or even trigger broader system instability. The fix addresses the root cause by implementing proper dynamic allocation and initialization patterns that comply with Linux kernel driver development standards and security best practices for embedded systems. Organizations should prioritize applying this patch to prevent potential service disruption and maintain system stability in environments where audio services are critical to operations.