CVE-2021-47070

What it actually does

Memory allocated by vmbus_alloc_ring() during uio_hv_generic probe is not released via vmbus_free_ring() on subsequent error paths, causing a leak.

Why it matters to the business

Repeated device probe failures can slowly exhaust kernel memory, leading to performance degradation or crashes in Hyper-V virtualized environments with high device churn.

How an attack unfolds

An attacker with the ability to repeatedly attach or reconfigure Hyper-V VMBus devices triggers the probe error path after successful ring allocation to accumulate leaked memory and induce resource pressure.

How to fix it

Apply the upstream kernel patch that adds the missing vmbus_free_ring() call in error paths; rebuild and deploy the fixed kernel image.

How to confirm the fix worked

Inspect the uio_hv_generic.c probe function for the presence of vmbus_free_ring() in all error exits after vmbus_alloc_ring(); confirm via kernel version or source diff.

Typical attack path

1. Gain access to attach or manipulate Hyper-V VMBus devices
2. Force repeated probe invocations that succeed on ring allocation but fail later
3. Accumulate unreleased memory across many attempts
4. Trigger system-wide memory pressure or OOM conditions

How to detect it

Review kernel logs for repeated uio_hv_generic probe failures; correlate with memory usage metrics and VMBus device attach events.

What your security team should do

• Prioritize patching kernel packages on all Hyper-V guest systems
• Monitor memory usage trends on hosts with frequent VMBus device events
• Test the fixed kernel in staging before broad rollout