CVE-2021-47502 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
ASoC: codecs: wcd934x: handle channel mappping list correctly
Currently each channel is added as list to dai channel list, however there is danger of adding same channel to multiple dai channel list which endups corrupting the other list where its already added.
This patch ensures that the channel is actually free before adding to the dai channel list and also ensures that the channel is on the list before deleting it.
This check was missing previously, and we did not hit this issue as we were testing very simple usecases with sequence of amixer commands.
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2021-47502 resides within the Linux kernel's Advanced SoC (ASoC) subsystem, specifically affecting the wcd934x codec driver implementation. This issue represents a critical flaw in channel management logic that can lead to memory corruption and system instability. The vulnerability manifests when handling channel mapping lists within the Digital Audio Interface (DAI) channel management system, where improper synchronization and validation mechanisms fail to prevent concurrent access issues. The wcd934x codec driver, commonly used in mobile and embedded audio systems, processes audio channel configurations through a complex list management system that requires careful handling of shared resources.
The technical flaw stems from inadequate validation checks during channel list operations within the ASoC framework, which operates under the broader context of the Linux kernel's sound subsystem. When audio channels are processed, each channel is intended to be added to the DAI channel list, but the absence of proper channel availability verification creates a race condition scenario. The vulnerability occurs because the system does not first confirm whether a channel is already present in any DAI channel list before attempting to add it, potentially resulting in duplicate entries across multiple lists. This condition violates fundamental principles of list management and resource allocation that are critical for maintaining system integrity. The flaw specifically impacts the channel mapping functionality within the codec driver, where audio channels must be properly managed to ensure correct audio routing and processing.
The operational impact of this vulnerability extends beyond simple audio quality degradation to potentially compromise system stability and security. When multiple audio operations occur concurrently or in rapid succession, the corrupted channel lists can cause unpredictable behavior in audio processing pipelines, leading to audio distortion, system crashes, or even privilege escalation opportunities. The vulnerability's exploitation potential increases in environments where audio applications perform complex channel mapping operations, particularly in embedded systems where the kernel's audio subsystem handles critical real-time processing tasks. Attackers could potentially leverage this flaw to disrupt audio services or gain unauthorized access to system resources, as the corrupted list structures may lead to memory access violations or data corruption in adjacent memory regions. This vulnerability affects systems using the wcd934x codec, which are commonly found in smartphones, tablets, and other mobile devices that rely on Linux-based operating systems for audio processing capabilities.
The mitigation strategy for CVE-2021-47502 involves implementing proper channel availability checks before list modifications and ensuring that channel removal operations verify list membership before execution. The patch addresses this issue by introducing validation mechanisms that check whether a channel is already present in any DAI channel list before adding it, and confirms channel existence before attempting deletion operations. This approach aligns with established security practices for resource management and prevents the type of list corruption that could lead to system instability. The fix demonstrates adherence to secure coding principles that are essential for kernel-level components, particularly those handling real-time audio processing. Organizations should prioritize updating their Linux kernel versions to include this patch, especially in embedded systems and mobile devices where audio functionality is critical. The vulnerability's resolution also highlights the importance of comprehensive testing scenarios that include complex channel mapping operations rather than simple command sequences, as indicated by the original testing limitations that allowed the issue to remain undetected. This fix contributes to the broader security posture of Linux-based systems by strengthening the kernel's audio subsystem against resource management vulnerabilities that could be exploited in various attack scenarios. The mitigation approach follows industry best practices for preventing list corruption and maintaining data integrity in concurrent access scenarios, aligning with security frameworks that emphasize proper resource validation and access control mechanisms.