# CVE-2026-89836: f2fs: fix folio_nr_pages() race after put in large folio invalidate

> A race condition in the Linux kernel's f2fs filesystem can cause livelocks and system instability during large folio invalidation.

- **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:** DEBIAN-CVE-2026-89836, GHSA-xprx-r7x7-gvjr, UBUNTU-CVE-2026-89836

## What is CVE-2026-89836?

CVE-2026-89836 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:

f2fs: fix folio_nr_pages() race after put in large folio invalidate

Our v6.18 based Android system is continuely suffering livelock and bad
page stat as shown in[1] which related to broken xarray slot status. By
investigating big folio operations within f2fs, we find below races and
fix it by get the nr_pages before drop the refcount and folio_lock.

f2fs_get_read_data_folio() calls f2fs_folio_put() before
folio_nr_pages() when invalidating a large folio from the page cache.
That unlocks the folio and drops the caller reference, leaving a window
where a concurrent truncate or folio split can shrink the compound folio
or free it before the invalidate range is computed. An undersized range
then leaves split sub-folios in mapping->i_pages, which can later
interact badly with truncate and reclaim (stale xarray entries and bad
page state when folio->mapping no longer matches the mapping being
truncated).

[1]
PID: 2594     TASK: ffffff8169b81580  CPU: 7    COMMAND: "Thread-3"
 #0 [ffffffc08ef2b8a0] xas_load at ffffffe52d1f42a4
 #1 [ffffffc08ef2b900] find_get_entries at ffffffe52c185798
 #2 [ffffffc08ef2bb60] truncate_inode_pages_range at ffffffe52c19e83c
 #3 [ffffffc08ef2bbc0] truncate_inode_pages_final at ffffffe52c19ec2c
 #4 [ffffffc08ef2bc20] f2fs_evict_inode at ffffffe52c4c8400
 #5 [ffffffc08ef2bcc0] evict at ffffffe52c2de9f4
 #6 [ffffffc08ef2bd00] iput at ffffffe52c2db1b4
 #7 [ffffffc08ef2bd30] dentry_unlink_inode at ffffffe52c2d7204
 #8 [ffffffc08ef2bd50] __dentry_kill at ffffffe52c2d3dcc
 #9 [ffffffc08ef2bd80] dput at ffffffe52c2d3c3c
 #10 [ffffffc08ef2bda0] __fput at ffffffe52c2b0a7c
 #11 [ffffffc08ef2bde0] ____fput at ffffffe52c2b1034
 #12 [ffffffc08ef2bdf0] task_work_run at ffffffe52beea200
 #13 [ffffffc08ef2be20] exit_to_user_mode_loop at ffffffe52bfbc17c
 #14 [ffffffc08ef2be80] el0_svc at ffffffe52d1f8e54
 #15 [ffffffc08ef2beb0] el0t_64_sync_handler at ffffffe52d1f8d10

## Which versions are affected by CVE-2026-89836?


## How do I fix CVE-2026-89836?

Apply the vendor's patch.

## Is CVE-2026-89836 being exploited?

There is no known exploitation of CVE-2026-89836 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89836 and fix it if it is affected.

What it is: CVE-2026-89836 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-2026-89836 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-2026-89836/ (Markdown: https://insights.sbomify.com/CVE-2026-89836/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89836
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89836
- OSV: https://osv.dev/vulnerability/CVE-2026-89836

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89836/
Summaries are generated and may contain mistakes; the official description above is the record.