# CVE-2024-26696: nilfs2: fix hang in nilfs_lookup_dirty_data_buffers()

> A race condition in the nilfs2 filesystem can cause a system hang, leading to denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 3 Apr 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-26696, DEBIAN-CVE-2024-26696, GHSA-cwr2-26gq-v2xr, UBUNTU-CVE-2024-26696

## What is CVE-2024-26696?

CVE-2024-26696 is a medium-severity vulnerability in Debian Debian Linux, published on 3 Apr 2024. 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:

nilfs2: fix hang in nilfs_lookup_dirty_data_buffers()

Syzbot reported a hang issue in migrate_pages_batch() called by mbind()
and nilfs_lookup_dirty_data_buffers() called in the log writer of nilfs2.

While migrate_pages_batch() locks a folio and waits for the writeback to
complete, the log writer thread that should bring the writeback to
completion picks up the folio being written back in
nilfs_lookup_dirty_data_buffers() that it calls for subsequent log
creation and was trying to lock the folio.  Thus causing a deadlock.

In the first place, it is unexpected that folios/pages in the middle of
writeback will be updated and become dirty.  Nilfs2 adds a checksum to
verify the validity of the log being written and uses it for recovery at
mount, so data changes during writeback are suppressed.  Since this is
broken, an unclean shutdown could potentially cause recovery to fail.

Investigation revealed that the root cause is that the wait for writeback
completion in nilfs_page_mkwrite() is conditional, and if the backing
device does not require stable writes, data may be modified without
waiting.

Fix these issues by making nilfs_page_mkwrite() wait for writeback to
finish regardless of the stable write requirement of the backing device.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2024-26696?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2024-26696?

Apply the vendor's patch.

## Is CVE-2024-26696 being exploited?

There is no known exploitation of CVE-2024-26696 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-26696 and fix it if it is affected.

What it is: CVE-2024-26696 is a medium-severity vulnerability in Debian Debian Linux, published on 3 Apr 2024. 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-2024-26696 in the wild and no public exploit code.

Affected product: Debian Debian 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-2024-26696/ (Markdown: https://insights.sbomify.com/CVE-2024-26696/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26696
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26696
- OSV: https://osv.dev/vulnerability/CVE-2024-26696

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26696/
Summaries are generated and may contain mistakes; the official description above is the record.