Recently identified and resolved, CVE-2024-42089 is a critical issue in the Linux kernel’s sound subsystem, specifically within the fsl-asoc-card driver. This vulnerability could lead to a NULL pointer dereference, which can cause system crashes, unexpected behavior, or potential denial-of-service (DoS) attacks if exploited under the right circumstances.

In plain language: This bug happens because the driver code tries to use a part of memory (priv->pdev) *before* it has been set up properly. If something goes wrong at just the right time, it can cause the audio driver—and sometimes the entire system—to fail.

Let's break down the details, see what went wrong, how it was fixed, and what you can do about it.

Where Did It Happen? (Technical Background)

The problem lives inside the driver for Freescale (NXP) audio cards in the ASoC (ALSA System on Chip) subsystem, part of the Linux kernel source. This specific driver (fsl-asoc-card.c) is often found in embedded devices, IoT, ARM development boards, and custom SoCs.

The vulnerable function is involved with initializing hardware audio multiplexers—specifically, the code below:

static int fsl_asoc_card_probe(struct platform_device *pdev)
{
    struct fsl_asoc_card_priv *priv;

    priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
    if (!priv)
        return -ENOMEM;

    // The bug: priv->pdev is assigned *after* functions that use it are called!
    ...
    ret = fsl_asoc_card_audmux_init(priv);
    ...
    priv->pdev = pdev; // <-- too late! Already used above
}

In the function fsl_asoc_card_audmux_init(), code tries to use priv->pdev to log errors. But at that moment, pdev hasn't been set, so its value is NULL.

Why Is This a Problem?

If an error occurs in fsl_asoc_card_audmux_init(), and the driver tries to print a log message with something like:

dev_err(&priv->pdev->dev, "error occurred\n");


But priv->pdev is NULL, so the kernel will attempt to access memory at address , causing a crash—normally a kernel panic or driver crash.

- Risk: Anyone able to trigger the buggy code path (for example, by configuring the sound hardware incorrectly or sending malformed hardware events) could crash the whole system.
- Impact: Potential for *local DoS* on devices using this driver, especially in custom hardware or embedded setups.

Who Is Affected?

- Any Linux system with the fsl-asoc-card driver loaded—with affected kernel versions prior to the fix.
- Most likely impact on embedded/IoT devices based on NXP/Freescale SoCs using the standard kernel driver.

How Was It Fixed?

The fix is simple, but important: move the line that assigns priv->pdev = pdev; to before any function that uses it is called.

Old code (vulnerable)

ret = fsl_asoc_card_audmux_init(priv);
priv->pdev = pdev; // Too late!

New code (fixed)

priv->pdev = pdev; // Set early
ret = fsl_asoc_card_audmux_init(priv);

This guarantees that, if any sub-function tries to use priv->pdev, it will not be a NULL pointer.

Patch reference:
- Linux kernel mailing list commit


## Proof-of-Concept / Exploit Details

While this bug needs hardware or a custom device-tree to trigger in practice, here’s how an exploit might look in theory:

Load the vulnerable driver on supported ARM hardware (like i.MX SoC boards).

2. Provide a bad or incomplete configuration for the sound card, forcing fsl_asoc_card_audmux_init() to fail.

The failure path in this function will trigger a logging macro using priv->pdev->dev.

4. Since priv->pdev == NULL, kernel panics—system crash / DoS.

Exploit test (pseudocode)

# Assume you have root and can control device-tree overlays on the system

# Replace the audio card configuration with one missing required properties
dtc -I dts -O dtb bad_audio_card.dts -o /boot/dtbs/bad_audio_card.dtbo

# Reboot, let the kernel load the driver with the bad config

# Result: Crash during boot/init, traced to NULL pointer dereference in fsl-asoc-card.c

References

- CVE-2024-42089 MITRE entry (awaiting publication)
- Linux kernel commit for the fix
- Linux ASoC subsystem documentation

Update your kernel!

If you use embedded boards or custom hardware with this driver, make sure you apply the latest kernel update or backport the patch.

Monitor device stability.

If you see unexplained audio driver failures or kernel panics during audio setup, check your kernel version.

Summary

CVE-2024-42089 wasn’t a “sexy” bug, but it’s a classic, dangerous C programming error: using a pointer before initializing it. In embedded or SoC Linux systems, these bugs matter—because they can bring down entire devices or critical systems. The fix is trivial, so upgrade now and stay safe.

If you want more details or want to dig into the code, follow the references above or reach out on the Linux kernel mailing list!

Timeline

Published on: 07/29/2024 17:15:11 UTC
Last modified on: 02/03/2025 15:23:12 UTC