CVE-2021-47071

What it actually does

Memory leak occurs in uio_hv_generic when vmbus_establish_gpadl() fails because recv_gpadl and send_gpadl are not updated, preventing hv_uio_cleanup() from releasing the associated buffers.

Why it matters to the business

Repeated triggering of the error condition can gradually exhaust kernel memory, leading to degraded performance or denial of service in Hyper-V guest environments over time.

How an attack unfolds

An attacker with local access or the ability to influence VMBus operations forces repeated failures in vmbus_establish_gpadl() during device initialization or error paths, causing buffers to be allocated without being freed.

How to fix it

Apply the upstream kernel commit that explicitly frees the buffers in the error handling path of uio_hv_generic; update to a kernel version containing the fix for CVE-2021-47071.

How to confirm the fix worked

Inspect the uio_hv_generic source for the explicit free of recv/send buffers after vmbus_establish_gpadl() failure; confirm the patch is present via kernel build logs or source review.

Typical attack path

1. Obtain local code execution or control over VMBus channel setup in a Hyper-V guest
2. Trigger error paths in vmbus_establish_gpadl() repeatedly
3. Accumulate unfreed GPADL buffers until memory pressure causes system instability

How to detect it

Review kernel logs for repeated vmbus_establish_gpadl failures; monitor slab or kmalloc allocations associated with uio_hv_generic for growth without corresponding frees.

What your security team should do

• Patch affected Linux kernels to the fixed version at the earliest maintenance window
• Monitor memory usage in Hyper-V guests for unexpected growth patterns
• Limit untrusted code execution inside guests where possible