CVE-2021-47523

What it actually does

Memory leak of a DMA-coherent buffer (rcvhdrtail_dummy_kvaddr) allocated during loadtime_init that is overwritten without freeing on subsequent reinit paths, causing permanent loss of the allocation.

Why it matters to the business

Repeated device resets on systems using Intel HFI1 InfiniBand adapters can gradually exhaust kernel memory, risking instability or crashes in long-running or high-availability environments.

How an attack unfolds

An attacker with privileges sufficient to trigger driver re-initialization (for example via hardware reset or module reload) repeatedly causes the allocation path to leak the DMA buffer without freeing prior instances, depleting system memory over time.

How to fix it

Upgrade the Linux kernel to a version containing the fix that moves allocation to hfi1_alloc_devdata() and deallocation to hfi1_free_devdata().

How to confirm the fix worked

Inspect kernel source to confirm dummy-tail allocation occurs once in hfi1_alloc_devdata and is freed exactly once in hfi1_free_devdata; run kmemleak or similar after repeated resets to verify no leak remains.

Typical attack path

1. Obtain local or administrative access to a system with HFI1 hardware
2. Trigger multiple device re-initializations or resets
3. Observe progressive kernel memory exhaustion

How to detect it

Enable kernel memory-leak detectors such as kmemleak and examine logs for unreleased dma_alloc_coherent calls associated with rcvhdrtail_dummy after device resets; review dmesg for repeated allocation failures.

What your security team should do

• Apply the kernel patch that relocates the allocation
• Monitor memory usage on HFI1-equipped systems after resets
• Restrict unprivileged access to driver reload or hardware reset operations