CVE-2021-47420

What it actually does

Memory allocated via kmalloc for ttm->sg in kfd_mem_dmamap_userptr is never released by kfree in kfd_mem_dmaunmap_userptr, causing a kernel memory leak on AMD KFD userptr DMA paths.

Why it matters to the business

Systems running affected Linux kernels with AMD GPUs may experience gradual memory exhaustion during repeated compute or graphics workloads, eventually triggering instability, OOM kills, or kernel panics that disrupt operations.

How an attack unfolds

An attacker with local access triggers repeated userptr DMA mappings through KFD compute workloads; each mapping leaks a small sg structure that accumulates until memory pressure forces denial of service.

How to fix it

Upgrade to a Linux kernel containing the upstream fix for the missing kfree in kfd_mem_dmaunmap_userptr; apply the patch or backport to any custom kernels still shipping the vulnerable amdkfd code.

How to confirm the fix worked

Confirm the presence of kfree(ttm->sg) inside kfd_mem_dmaunmap_userptr in the running kernel source tree or verify the kernel version includes commit resolving the ttm->sg leak.

Typical attack path

1. Obtain local unprivileged access on a Linux system with AMD GPU and KFD enabled
2. Repeatedly issue userptr DMA mapping operations via ROCm or OpenCL workloads
3. Monitor kernel memory counters while mappings accumulate without release
4. Trigger OOM conditions or kernel instability once leak exhausts available memory

How to detect it

Review kernel logs and slab allocator statistics for unusual growth in amdkfd-related allocations; correlate spikes with KFD userptr mapping activity in dmesg or perf traces.

What your security team should do

• Prioritize kernel upgrades on all AMD GPU compute nodes within the next maintenance window
• Monitor kernel memory usage trends on systems exposing KFD to untrusted workloads
• Restrict access to ROCm/KFD interfaces until patches are deployed