# CVE-2026-89961: powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population

> Incorrect PFN tracking in PowerPC memory management can lead to improper head/tail page mapping decisions, potentially causing memory corruption or instability.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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-101217, BELL-CVE-2026-89961, DEBIAN-CVE-2026-89961, GHSA-25fw-r826-pmc4, UBUNTU-CVE-2026-89961

## What is CVE-2026-89961?

CVE-2026-89961 is a high-severity 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:

powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population

vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN
offset within a compound page and to decide whether the current vmemmap
slot should be populated as a head page mapping or should reuse a tail
page mapping.

However, addr_pfn is advanced manually in parallel with addr.  The loop
itself progresses in vmemmap address space, so each PAGE_SIZE step in addr
covers PAGE_SIZE / sizeof(struct page) struct page slots.  Since addr_pfn
is compared against nr_pages in data-PFN units, it should advance by the
same number of PFNs.  The existing manual increments do not match that and
therefore do not reliably track the PFN corresponding to the current addr.

As a result, pfn_offset can be computed from the wrong PFN and the code
can make the head/tail decision for the wrong compound-page position.

Fix this by deriving addr_pfn directly from the current vmemmap address
instead of carrying it as loop state.

## Which versions are affected by CVE-2026-89961?


## How do I fix CVE-2026-89961?

Apply the vendor's patch.

## Is CVE-2026-89961 being exploited?

There is no known exploitation of CVE-2026-89961 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89961 and fix it if it is affected.

What it is: CVE-2026-89961 is a high-severity 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-2026-89961 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-2026-89961/ (Markdown: https://insights.sbomify.com/CVE-2026-89961/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89961
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89961
- OSV: https://osv.dev/vulnerability/CVE-2026-89961

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89961/
Summaries are generated and may contain mistakes; the official description above is the record.