# CVE-2026-89841: f2fs: only redirty pinned folios in redirty_blocks

> A reference counting error in the f2fs filesystem can cause a use-after-free condition, leading to kernel crashes and denial of service.

- **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:** BELL-CVE-2026-89841, DEBIAN-CVE-2026-89841, GHSA-9c6f-r39g-mhg4, UBUNTU-CVE-2026-89841

## What is CVE-2026-89841?

CVE-2026-89841 is a high-severity use after free 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:

f2fs: only redirty pinned folios in redirty_blocks

redirty_blocks() pins folios with read_cache_folio() and then walks the
same range again with filemap_lock_folio() to redirty them and drop the
references it took.

Commit 5951fee46bef ("f2fs: Use a folio in redirty_blocks()") changed
the second pass to a do/while loop. If read_cache_folio() fails before
anything is pinned, page_idx does not advance but the cleanup loop still
runs once.

If readahead has already populated the failed folio in page cache, that
extra iteration finds it and folio_put_refs(folio, 2) drops one
reference too many. Later drop_caches or reclaim can then report
"BUG: Bad page state".

Only redirty the range that was pinned successfully.

## Which versions are affected by CVE-2026-89841?


## How do I fix CVE-2026-89841?

Apply the vendor's patch.

## Is CVE-2026-89841 being exploited?

There is no known exploitation of CVE-2026-89841 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89841 and fix it if it is affected.

What it is: CVE-2026-89841 is a high-severity use after free 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-2026-89841 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-2026-89841/ (Markdown: https://insights.sbomify.com/CVE-2026-89841/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89841
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89841
- OSV: https://osv.dev/vulnerability/CVE-2026-89841

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89841/
Summaries are generated and may contain mistakes; the official description above is the record.