CVE-2021-47033

What it actually does

The vulnerability is a DMA mapping leak in the mt7615 wireless driver where the first pointer in the txp structure is not unmapped after TX skb operations, leaving DMA mapping entries allocated and unreleased.

Why it matters to the business

Systems using mt7615-based wireless hardware may experience gradual resource exhaustion, leading to driver instability, degraded network performance, or system crashes under sustained TX load.

How an attack unfolds

An attacker triggers repeated TX skb transmissions through the mt7615 driver (via local processes or crafted wireless traffic) to cause the driver to allocate DMA mappings without releasing the first txp pointer entry, exhausting available DMA resources over time.

How to fix it

Update the Linux kernel to a version that includes the mt76 mt7615 TX skb DMA unmap fix so the first txp pointer is properly released.

How to confirm the fix worked

Inspect the mt7615 driver source after the update to confirm an unmap operation is performed on the first txp pointer; test TX paths under load and verify no DMA mapping leaks appear in kernel logs.

Typical attack path

1. Gain ability to initiate TX operations on mt7615 hardware
2. Generate high volume of TX skbs that exercise the unmap path
3. Accumulate unmapped DMA entries until resource limits are reached
4. Observe resulting driver or kernel instability

How to detect it

Review kernel logs for mt76 or mt7615 driver messages mentioning DMA mappings, txp unmap failures, or resource exhaustion; correlate with wireless TX activity.

What your security team should do

• Prioritize kernel updates on systems with mt7615 wireless hardware
• Monitor kernel logs for DMA-related warnings on affected devices
• Limit exposure by restricting untrusted local processes from generating high-volume TX traffic until patched