CVE-2021-47021

What it actually does

Memory leak in mt7915 wireless driver during device unregister because mt7915_tx_token_put is not invoked before mt76_free_pending_txwi, leaving allocated TX tokens unreleased.

Why it matters to the business

Gradual memory exhaustion on affected wireless systems can degrade performance or cause instability during repeated device registration cycles, increasing operational overhead for hardware maintenance.

How an attack unfolds

An attacker with local privileges or physical access repeatedly triggers device unregister/register sequences to accumulate unreleased memory allocations until system resources are depleted.

How to fix it

Apply a Linux kernel update that ensures mt7915_tx_token_put is called before mt76_free_pending_txwi inside mt7915_unregister_device.

How to confirm the fix worked

Inspect kernel source for the corrected call order in mt7915_unregister_device and confirm the patch is present after upgrade.

Typical attack path

1. Obtain local access or hardware control on target system
2. Trigger mt7915 device unregister operations
3. Repeat registration cycles to accelerate memory consumption
4. Observe system degradation from exhausted memory

How to detect it

Review kernel logs and memory profiling for unreleased allocations tied to mt76 driver unregister paths; correlate with device hotplug events.

What your security team should do

• Prioritize kernel updates for systems using mt7915 hardware
• Monitor memory usage trends on wireless-enabled hosts
• Audit device driver initialization logs for repeated register/unregister events