# CVE-2026-89809: drm/amdkfd: fix scope of mqd_mgr dereference in pqm_debugfs_mqds

> A local attacker can cause a kernel crash by reading a debugfs file while a KFD queue is active, leading to 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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101625, DEBIAN-CVE-2026-89809, GHSA-634r-724x-3g6w, UBUNTU-CVE-2026-89809

## What is CVE-2026-89809?

CVE-2026-89809 is a vulnerability in Linux, published on 16 Sep 2026. 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/amdkfd: fix scope of mqd_mgr dereference in pqm_debugfs_mqds

Reading /sys/kernel/debug/kfd/mqds while a process holds an active KFD
queue triggers a NULL pointer dereference because the for loop that
calls mqd_mgr->debugfs_show_mqd() is incorrectly placed outside the
if (pqn->q) block that initializes mqd_mgr.

The queue list can contain entries where pqn->q is NULL (kernel queues
where only pqn->kq is valid). In the original code:

  if (pqn->q) {
      ...
      mqd_mgr = q->device->dqm->mqd_mgrs[mqd_type];
      size = mqd_mgr->mqd_stride(...);
  }

  for (xcc = 0; xcc < num_xccs; xcc++) {  // WRONG: outside if block
      mqd = q->mqd + size * xcc;
      r = mqd_mgr->debugfs_show_mqd(m, mqd);
  }

When iterating over a queue node where pqn->q is NULL:
1. The if (pqn->q) block is skipped
2. mqd_mgr remains uninitialized (NULL from declaration)
3. The for loop executes anyway
4. mqd_mgr->debugfs_show_mqd(m, mqd) dereferences NULL

The crash manifests as:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  #PF: supervisor instruction fetch in kernel mode
  RIP: 0010:0x0
  Call Trace:
   pqm_debugfs_mqds+0x10c/0x1d0 [amdgpu]
   kfd_debugfs_mqds_by_process+0x9b/0x110 [amdgpu]
   seq_read_iter+0x132/0x4b0
   ...

Fix by moving the for loop inside the if (pqn->q) block, so mqd_mgr
and related variables are only used when properly initialized.

(cherry picked from commit 8bfe29d5c798940f797aa24135d2734c3ffce9de)

## Which versions are affected by CVE-2026-89809?


## How do I fix CVE-2026-89809?

Apply the vendor's patch.

## Is CVE-2026-89809 being exploited?

There is no known exploitation of CVE-2026-89809 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89809 and fix it if it is affected.

What it is: CVE-2026-89809 is a vulnerability in Linux, published on 16 Sep 2026. 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-2026-89809 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-2026-89809/ (Markdown: https://insights.sbomify.com/CVE-2026-89809/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89809
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89809
- OSV: https://osv.dev/vulnerability/CVE-2026-89809

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89809/
Summaries are generated and may contain mistakes; the official description above is the record.