CVE-2021-47502

What it actually does

Improper handling of channel mapping lists in the wcd934x ASoC codec driver allows the same channel to be added to multiple DAI lists, corrupting list structures and violating memory integrity.

Why it matters to the business

May trigger kernel crashes or audio subsystem instability on affected Linux systems during complex sound configuration sequences, increasing downtime risk for audio-enabled devices.

How an attack unfolds

An attacker with local access issues a crafted sequence of amixer commands that reuse channels across DAI lists; the missing free-channel check then corrupts list pointers, potentially leading to memory corruption or denial of service.

How to fix it

Apply the upstream patch that adds checks ensuring a channel is free before insertion and present before deletion; rebuild and deploy updated kernel packages containing the fix.

How to confirm the fix worked

Review kernel git history for the commit titled 'ASoC: codecs: wcd934x: handle channel mapping list correctly', confirm the added list-membership checks are present, and retest with complex amixer sequences.

Typical attack path

1. Obtain local shell or process execution on target system
2. Load or trigger wcd934x codec driver paths
3. Execute sequence of ALSA mixer commands that reuse channel mappings
4. Trigger list corruption via simultaneous DAI operations

How to detect it

Search kernel logs for list corruption warnings or oops involving wcd934x or dai channel lists; inspect recent ALSA mixer command history on affected hosts.

What your security team should do

• Prioritize kernel updates on systems using wcd934x or similar ASoC codecs
• Monitor for audio-related oops or list corruption panics in kernel logs
• Restrict unprivileged access to ALSA mixer controls where feasible