# CVE-2025-40288: drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices

> A local attacker can trigger a kernel crash on AMD APU systems by accessing uninitialized VRAM manager structures, causing a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40288, DEBIAN-CVE-2025-40288, GHSA-5ppv-prh8-hj77, ROOT-OS-DEBIAN-11-CVE-2025-40288, ROOT-OS-DEBIAN-12-CVE-2025-40288, ROOT-OS-DEBIAN-13-CVE-2025-40288, ROOT-OS-UBUNTU-2204-CVE-2025-40288, ROOT-OS-UBUNTU-2404-CVE-2025-40288, UBUNTU-CVE-2025-40288

## What is CVE-2025-40288?

CVE-2025-40288 is a vulnerability in Linux, published on 6 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices

Previously, APU platforms (and other scenarios with uninitialized VRAM managers)
triggered a NULL pointer dereference in `ttm_resource_manager_usage()`. The root
cause is not that the `struct ttm_resource_manager *man` pointer itself is NULL,
but that `man->bdev` (the backing device pointer within the manager) remains
uninitialized (NULL) on APUs—since APUs lack dedicated VRAM and do not fully
set up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to
acquire `man->bdev->lru_lock`, it dereferences the NULL `man->bdev`, leading to
a kernel OOPS.

1. **amdgpu_cs.c**: Extend the existing bandwidth control check in
   `amdgpu_cs_get_threshold_for_moves()` to include a check for
   `ttm_resource_manager_used()`. If the manager is not used (uninitialized
   `bdev`), return 0 for migration thresholds immediately—skipping VRAM-specific
   logic that would trigger the NULL dereference.

2. **amdgpu_kms.c**: Update the `AMDGPU_INFO_VRAM_USAGE` ioctl and memory info
   reporting to use a conditional: if the manager is used, return the real VRAM
   usage; otherwise, return 0. This avoids accessing `man->bdev` when it is
   NULL.

3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function)
   data write path. Use `ttm_resource_manager_used()` to check validity: if the
   manager is usable, calculate `fb_usage` from VRAM usage; otherwise, set
   `fb_usage` to 0 (APUs have no discrete framebuffer to report).

This approach is more robust than APU-specific checks because it:
- Works for all scenarios where the VRAM manager is uninitialized (not just APUs),
- Aligns with TTM's design by using its native helper function,
- Preserves correct behavior for discrete GPUs (which have fully initialized
  `man->bdev` and pass the `ttm_resource_manager_used()` check).

v4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian)

## Which versions are affected by CVE-2025-40288?


## How do I fix CVE-2025-40288?

Apply the vendor's patch.

## Is CVE-2025-40288 being exploited?

There is no known exploitation of CVE-2025-40288 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40288 and fix it if it is affected.

What it is: CVE-2025-40288 is a vulnerability in Linux, published on 6 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40288 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40288/ (Markdown: https://insights.sbomify.com/CVE-2025-40288/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40288
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40288
- OSV: https://osv.dev/vulnerability/CVE-2025-40288

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-40288/
Summaries are generated and may contain mistakes; the official description above is the record.