CVE-2021-47332

What it actually does

Missing NULL pointer check before calling free_pages_exact() in ALSA usx2y driver allows the function to receive an invalid address, resulting in a kernel oops or panic.

Why it matters to the business

Systems using affected USB audio hardware may experience unexpected kernel crashes, leading to downtime, loss of audio functionality, and potential data corruption in memory-sensitive workloads.

How an attack unfolds

An attacker with local access triggers the usx2y audio path that passes a NULL address to free_pages_exact(), causing the kernel to dereference invalid memory and crash the system.

How to fix it

Apply the upstream kernel patch that adds the NULL check before free_pages_exact() or upgrade to a Linux kernel version containing commit resolving CVE-2021-47332.

How to confirm the fix worked

Verify the presence of the NULL check in sound/usb/usx2y/usbusx2y.c or confirm the running kernel is newer than the vulnerable release containing the fix.

Typical attack path

1. Obtain local access to a Linux system with the usx2y ALSA driver loaded
2. Perform operations that exercise the audio buffer release code path
3. Supply input that results in a NULL address being passed to free_pages_exact()
4. Trigger kernel oops and system instability or reboot

How to detect it

Review kernel logs for oops or panic entries referencing usx2y or free_pages_exact with NULL address; correlate with audio device attach events.

• usx2y
• free_pages_exact
• ALSA: usx2y

What your security team should do

• Prioritize kernel updates on any systems exposing ALSA USB audio drivers
• Monitor for kernel oops reports involving usx2y
• Restrict untrusted local access until patches are applied