# CVE-2026-93233: drm/nouveau/dmem: fix callocated underflow on large folio split

> A local attacker can trigger an integer underflow in the nouveau driver, causing memory leaks and preventing resource reclamation, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-93233, GHSA-xp29-rgmw-chx9, UBUNTU-CVE-2026-93233

## What is CVE-2026-93233?

CVE-2026-93233 is a vulnerability in Linux, published on 24 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/nouveau/dmem: fix callocated underflow on large folio split

nouveau_dmem_folio_free() drops chunk->callocated once per freed folio,
while a large (compound) device-private folio is only counted once when
it is allocated.  When such a folio is split, the mm core invokes
->folio_split() (nouveau_dmem_folio_split()) once for each new
sub-folio, but the hook only fixes up the sub-folio metadata and leaves
chunk->callocated unchanged.

Each resulting sub-folio is later freed separately, so after a split
the single allocation (+1) is met by N frees (-N), leaving
chunk->callocated short by N-1.  On the first split/free cycle it
underflows: WARN_ON(!chunk->callocated) fires, the unsigned counter
wraps and never returns to zero, so the chunk can no longer be
reclaimed (nouveau_dmem_fini() also warns on the leaked count).

Account for the new sub-folio in the split hook, under the same lock as
nouveau_dmem_folio_free(), so the count stays balanced.

## Which versions are affected by CVE-2026-93233?


## How do I fix CVE-2026-93233?

Apply the vendor's patch.

## Is CVE-2026-93233 being exploited?

There is no known exploitation of CVE-2026-93233 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93233 and fix it if it is affected.

What it is: CVE-2026-93233 is a vulnerability in Linux, published on 24 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-2026-93233 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-2026-93233/ (Markdown: https://insights.sbomify.com/CVE-2026-93233/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93233
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93233
- OSV: https://osv.dev/vulnerability/CVE-2026-93233

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93233/
Summaries are generated and may contain mistakes; the official description above is the record.