CVE-2021-47384

What it actually does

The vulnerability allows a NULL pointer dereference in the w83793 hwmon driver when a crafted sensor register value satisfying specific bit conditions is read from the device, triggered after changes to subclient device handling.

Why it matters to the business

Systems using the affected hardware monitoring driver may experience kernel crashes leading to denial of service, requiring reboots and potential loss of monitoring on servers with w83793 chips; low exploitability limits widespread impact but affects stability in embedded or server environments.

How an attack unfolds

An attacker with the ability to influence or emulate sensor device responses supplies a register value matching the pattern that bypasses null checks, causing the driver to dereference an invalid pointer during value processing after the switch to managed I2C dummy devices.

How to fix it

Update to a Linux kernel version containing the fix that removes the unnecessary lm75[] structure field and associated checks in the w83793 driver; rebuild and deploy the patched kernel across affected distributions.

How to confirm the fix worked

Confirm the patch is applied by inspecting the w83793 driver source for removal of lm75[] and related conditional logic, then test hardware sensor reads on w83793-equipped systems to ensure no dereference occurs.

Typical attack path

1. Identify systems exposing the w83793 hwmon driver via loaded kernel modules or hardware presence
2. Craft or inject a sensor register read response matching the bit pattern 0b0xyz1xyz
3. Trigger the driver's read path through normal monitoring queries or direct hardware access
4. Cause NULL dereference leading to kernel oops or panic

How to detect it

Review kernel logs and dmesg output for null pointer dereference oops involving w83793 or hwmon code paths; correlate with hardware sensor query events.

What your security team should do

• Prioritize kernel updates on systems with w83793 or related hwmon drivers
• Monitor kernel logs for null pointer oops in hwmon paths
• Disable unnecessary hwmon drivers if hardware is not present