Linux Kernel ASoC FSL_MICFIL Clock Management Flaw

Executive Summary

This vulnerability is in the Linux kernel's ASoC subsystem, specifically in the fsl_micfil driver. It involves improper management of the mclk clock signal. The hw_params() function enables the clock unconditionally, while hw_free() disables it unconditionally. However, the PCM core does not guarantee a 1:1 pairing between these calls, leading to issues where hw_free() might run without hw_params() or hw_params() might be called multiple times. This can trigger a warning about the clock already being disabled and leak an enable reference, making the clock ungateable.

The fix involves using the existing mclk_flag to guard both the enable and disable operations, similar to how it is done in the fsl_sai.c driver.

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Detection Guidance

This vulnerability is specific to the Linux kernel's ASoC subsystem and the fsl_micfil driver. Detection requires checking the kernel version and the presence of the vulnerable code in the driver. Use commands like 'uname -a' to check the kernel version and 'dmesg | grep fsl_micfil' to see if the driver is loaded and if any warnings related to mclk are present.

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Impact Analysis

This vulnerability primarily affects systems using the Linux kernel with the fsl_micfil driver, such as embedded devices with audio capabilities. It could lead to system instability or crashes due to improper clock management. In severe cases, it might cause audio subsystem failures or unexpected behavior in applications relying on audio functionality.

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Mitigation Strategies

Apply the latest kernel update that includes the fix for this vulnerability. If an update is not immediately available, consider disabling the fsl_micfil driver if it is not required for your system. Monitor kernel mailing lists or security advisories for updates.

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