CVE-2024-57800 - Linux Kernel ALSA DMA Mapping Error Check Vulnerability (Explained With Example)

The Linux Kernel is the core of most Linux-based systems—it’s what makes your computer "tick." So, when a vulnerability is discovered, it’s important to understand what happened, how it was fixed, and how it can impact you or your servers. In this post, we break down CVE-2024-57800, a Linux Kernel vulnerability related to the ALSA sound system memory allocation, focusing on DMA mapping and how it was resolved.

What Is CVE-2024-57800?

CVE-2024-57800 is a vulnerability resolved in the Linux kernel's Advanced Linux Sound Architecture (ALSA) memory allocator. The issue was about how ALSA checked for Direct Memory Access (DMA) mapping errors.

The Vulnerability

When devices (like sound cards) need fast access to system memory, they use DMA. But not every DMA mapping works—sometimes, the mapping fails and must be checked properly. Previously, ALSA was using raw address value checks to see if a DMA mapping failed. However, Linux provides a safer helper function called dma_mapping_error() to make this check reliable across different hardware platforms.

Here’s a warning you could see with faulty code and debug enabled (CONFIG_DMA_API_DEBUG)

DMA-API: snd_hda_intel 000:03:00.1: device driver failed to check map error[device address=x00000000ffff000] [size=20480 bytes] [mapped as single]
WARNING: CPU: 28 PID: 2255 at kernel/dma/debug.c:1036 check_unmap+x1408/x243
CPU: 28 UID: 42 PID: 2255 Comm: wireplumber Tainted: G  W L  6.12.-10-133577cad6bf48e5a7848c4338124081393bfe8a+ #759
debug_dma_unmap_page+xe9/xf
snd_dma_wc_free+x85/x130 [snd_pcm]
snd_pcm_lib_free_pages+x1e3/x440 [snd_pcm]
snd_pcm_common_ioctl+x1c9a/x296 [snd_pcm]
snd_pcm_ioctl+x6a/xc [snd_pcm]
...

The Flawed Code (Before The Fix)

Here’s a simplified example of how drivers might have previously checked for DMA mapping errors, which is NOT always safe:

dma_addr_t addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE);

if (addr == ) {
    // BAD: This might not catch all mapping failures on all platforms
    printk(KERN_ERR "DMA mapping failed!\n");
    return -1;
}

This can break on some systems where is actually a valid DMA address, missing real failures, or misdetecting success as failure.

The Safer Way: Using dma_mapping_error()

Linux recommends using dma_mapping_error() to check if a DMA mapping has failed. It handles the edge cases for you.

The Fixed Code

dma_addr_t addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE);

if (dma_mapping_error(dev, addr)) {
    // GOOD: This is portable and correct
    printk(KERN_ERR "DMA mapping failed!\n");
    return -1;
}

The kernel documentation dma-api.rst says:

> Always use dma_mapping_error() to check for DMA mapping failures.

How Was It Fixed?

The Linux kernel maintainers updated the ALSA memory allocation code to use dma_mapping_error() instead of checking the address directly. This change patch ensures that drivers won’t misdetect failures and will behave correctly across all supported platforms.

You can take a look at the relevant patch in the kernel sources

- Patch: ALSA: memalloc: prefer dma_mapping_error() over explicit address checking

Exploitability

This is technically a potential reliability bug rather than a classic security exploit. However, here’s what could happen:

- Denial of Service: If faulty DMA mapping isn’t properly detected, the driver might attempt to use bad memory addresses, leading to kernel panics or crashes.
- System Instability: Applications using ALSA (like Firefox or audio editors) might behave unpredictably or crash.
- Privilege Escalation: In extreme, contrived scenarios, mishandled DMA could be abused by a malicious driver to manipulate kernel memory, but that’s not the central issue in this CVE.

As of now, no public exploit code is known for this bug. But, any kernel bug raising a warning and accepting tainted memory could, in theory, become a stepping-stone for local attacks if combined with other vulnerabilities.

How To Protect Yourself

- Update Your Kernel: Most modern distributions (Ubuntu, Fedora, Debian, etc.) have already merged the fix in recent kernel versions. Just keep your system up-to-date!
- Check Your Logs: If you see DMA-API warnings mentioning ALSA or snd_hda_intel, you might be running an old kernel.
- For Developers: Always use dma_mapping_error() in your driver code to future-proof quality and safety.

References

- Linux Kernel Patch Discussion: ALSA: memalloc: prefer dma_mapping_error()...
- Linux Documentation - DMA-API
- CVE-2024-57800 entry in MITRE (*pending*)

Summary

CVE-2024-57800 is a kernel bug fixed by using the correct DMA error-checking function in ALSA’s memory allocation. It’s a great example of why following best practices in error handling matters—your system stays stable, and the code works everywhere Linux runs. Always prefer specialized helpers like dma_mapping_error() over manual checks!

Timeline

Published on: 01/11/2025 13:15:30 UTC
Last modified on: 05/04/2025 10:05:01 UTC