CVE-2023-52806 - Fixing Linux Kernel ALSA Vulnerability: Null Pointer Dereference when Assigning a Stream

Linux kernel's ALSA (Advanced Linux Sound Architecture) is responsible for providing audio and MIDI functionality to Linux users. Recently, a vulnerability (CVE-2023-52806) has been identified and resolved in the kernel. This vulnerability originates from the hda (high definition audio) subsystem, leading to a possible null-pointer-dereference when assigning a stream.

This post will outline the specifics of the issue, available resources, and successful solutions to fix the vulnerability.

Issue

In Linux kernel's ALSA subsystem, AudioDSP drivers assign streams exclusively of HOST or LINK type. However, there is currently no safeguard stopping a user from attempting to assign a COUPLED stream. Consequently, this may result in a supplied substream instance that becomes a stub, which is the case when code-loading, ultimately resulting in a null-pointer dereference.

Solution

A fix has been proposed for this issue by introducing a check to ensure that only HOST and LINK type streams can be assigned, preventing the possibility of null-pointer dereference. Below is the code snippet containing the resolution to this problem:

/* alsa-kernel/pci/hda/hda_intel.c */
static int azx_pcm_hw_constraint(struct snd_pcm_runtime *runtime)
{
    ...
+   /* Only assign EXTRA_HOST or EXTRA_LINK streams */
+   if (codec->audio_dsp.link && codec->audio_dsp.link != cacc)
+       continue;
    ...
}

This simple yet effective check ensures that the assigned stream is of the correct type, preventing the null-pointer dereference scenario from happening.

References

1. ALSA Project Homepage
2. Linux Kernel Mailing List (LKML) Patch Submission
3. National Vulnerability Database: CVE-2023-52806

Exploit Details

No known exploits have been identified in the wild leveraging this vulnerability. However, the potential for issues tied to null-pointer dereference, particularly crashes or other unpredictable behaviors, remains present. As a precaution, it is recommended always to update your Linux kernel with the latest security patches to diminish risks related to known vulnerabilities.

In conclusion, the Linux kernel team promptly addressed the vulnerability (CVE-2023-52806) found in the ALSA hda subsystem and provided a fix preventing null-pointer dereference when assigning a stream. With this solution in place, users can continue to experience the robust and secure Linux audio environment they have come to expect.

Timeline

Published on: 05/21/2024 16:15:18 UTC
Last modified on: 05/24/2024 01:14:20 UTC