CVE-2021-47253

What it actually does

Repeated kzalloc allocation for the DC wrapper to DMUB during dm_dmub_hw_init on every resume without corresponding free on suspend creates an unbounded kernel memory leak in the AMD display driver.

Why it matters to the business

Linux systems with AMD GPUs can slowly exhaust kernel memory after many suspend/resume cycles, leading to degraded performance, application failures, or eventual system instability; low exploitability and long public availability reduce immediate operational urgency.

How an attack unfolds

An attacker with local access repeatedly triggers suspend/resume cycles (via power management commands or scripts) to force repeated allocations in dm_resume o dm_dmub_hw_init o dc_dmub_srv_create, gradually consuming kernel memory until the system becomes unusable.

How to fix it

Apply the upstream kernel fix that guards the kzalloc with a check for prior allocation so memory is created only once; update to a kernel version containing commit resolving the DMUB hw_init leak and reboot affected systems.

How to confirm the fix worked

Confirm the patch is present by inspecting the dmub_hw_init or dc_dmub_srv_create code for an allocation guard; monitor kernel memory usage across multiple suspend/resume cycles to verify no repeated growth in the affected structures.

Typical attack path

1. Obtain local user access on a Linux system with AMD display hardware
2. Repeatedly invoke suspend and resume operations through power management interfaces or automation
3. Trigger dm_resume path which unconditionally allocates new DMUB wrapper memory
4. Accumulate leaked kernel memory across cycles until resource exhaustion

How to detect it

Review kernel logs for repeated kzalloc calls or growing allocations tied to dmub or dc_dmub_srv_create structures during suspend/resume events; correlate with high slab memory usage in /proc/meminfo or slabinfo over time.

What your security team should do

• Prioritize patching on systems that frequently use suspend/resume (laptops, mobile workstations)
• Verify kernel version against the fix commit for the AMD DMUB memory allocation guard
• Include AMD display driver memory usage in routine kernel leak monitoring