CVE-2024-56533

What it actually does

The vulnerability replaces snd_card_free() with snd_card_free_when_closed() in the ALSA usx2y USB audio driver disconnect callback to prevent blocking on file descriptor release, which could trigger a soft lockup by stalling upper-layer USB ioctls.

Why it matters to the business

Systems using specific USB audio hardware may experience temporary unresponsiveness or watchdog-induced reboots during device disconnection, disrupting audio-dependent operations with low overall prevalence in standard deployments.

How an attack unfolds

An attacker with local or physical access triggers USB disconnection of a usx2y device, invoking the flawed callback that waits indefinitely on open file descriptors and blocks kernel USB handling, resulting in a soft lockup DoS condition.

How to fix it

Update the Linux kernel to a version incorporating commit 24fe9f7ca83ec9acf765339054951f5cd9ae5c5d which switches the usx2y driver to snd_card_free_when_closed().

How to confirm the fix worked

Verify the presence of snd_card_free_when_closed() in the usx2y disconnect path via kernel source inspection or confirm the fixed commit is included in the running kernel build.

Typical attack path

1. Identify a system with usx2y USB audio device attached
2. Initiate device disconnection via physical removal or software eject
3. Trigger the USB disconnect callback in the kernel driver
4. Observe blocking behavior leading to soft lockup or system stall

How to detect it

Review kernel logs for soft lockup or watchdog messages referencing USB disconnect or ALSA card free operations during device removal events.

• soft lockup.*usx2y
• snd_card_free.*disconnect
• ALSA.*USB.*blocked

What your security team should do

• Apply the kernel update containing the referenced commit at the earliest maintenance window
• Monitor for soft lockup reports involving USB or ALSA subsystems
• Limit untrusted USB device connections on affected systems until patched