A vulnerability was discovered in the Linux kernel, specifically in the ALSA (Advanced Linux Sound Architecture) subsystem related to the usx2y driver. This vulnerability has the potential to cause a soft lockup in the kernel, affecting system stability and performance. This post provides an overview of the vulnerability, its impact, remediation, and related links.

Vulnerability Details

In the Linux kernel's ALSA subsystem, the USB disconnection callback is expected to be short and not too long waiting. However, the current implementation uses snd_card_free() at disconnection, which waits for the close of all used file descriptors, causing potential delays. These delays can, in turn, block upper layer USB ioctls and may trigger a soft lockup in the kernel.

The vulnerability is assigned CVE-2024-56533 and classified as a medium severity issue.

The following is an example of the vulnerable code in the ALSA usx2y driver

static void snd_usx2y_card_disconnect(struct usb_device *device, void *ptr)
{
    struct usx2ydev *usx2y = ptr;
    struct snd_card *card;

    if (!usx2y)
        return;
    card = usx2y->card;
    if (card)
        snd_card_free(card);
}

For resolving this issue, you should replace the snd_card_free() function with the snd_card_free_when_closed() function. This will ensure that the function returns immediately while the release of resources is carried out asynchronously by the card device release at the last close.

Here is the modified, secure version of the code

static void snd_usx2y_card_disconnect(struct usb_device *device, void *ptr)
{
    struct usx2ydev *usx2y = ptr;
    struct snd_card *card;

    if (!usx2y)
        return;
    card = usx2y->card;
    if (card)
        snd_card_free_when_closed(card);
}

Remediation

To address this issue, developers and system administrators should apply the patch and update their Linux kernel installations. The patch, which implements the suggested fix, is available at Linux Kernel Patch.

Original References

- [Linux Kernel Mailing List] (https://lore.kernel.org/patchwork/patch/790885/)
- ALSA Project
- [CVE Details] (https://www.cvedetails.com/cve/CVE-2024-56533/)

Conclusion

The Linux kernel vulnerability in ALSA: usx2y driver has been resolved by using snd_card_free_when_closed() at disconnection. Developers and system administrators should take note of this issue and apply the necessary updates to their systems to ensure stability and security. Remember to always keep your kernel updated and to monitor for new vulnerabilities and patches as they become available in the constantly evolving world of cyber security.

Timeline

Published on: 12/27/2024 14:15:32 UTC
Last modified on: 01/20/2025 06:22:23 UTC