# CVE-2026-89830: f2fs: fix valid block count leak on data block allocation failure

> A local attacker can cause a permanent block count leak in the f2fs filesystem, leading to resource exhaustion and denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **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-2026-89830, DEBIAN-CVE-2026-89830, GHSA-c5cf-c6gm-hv9c, UBUNTU-CVE-2026-89830

## What is CVE-2026-89830?

CVE-2026-89830 is a denial of service 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 valid block count leak on data block allocation failure

In __allocate_data_block(), when allocating a new data block
(dn->data_blkaddr == NULL_ADDR), inc_valid_block_count() is
called first to increment total_valid_block_count and i_blocks.
If the subsequent f2fs_allocate_data_block() fails, the function
returns the error directly without rolling back the
already-incremented block counts, causing a permanent leak.

Fix this by calling dec_valid_block_count() to undo the
increment before returning the error. The condition
old_blkaddr == NULL_ADDR precisely identifies the case where
inc_valid_block_count() was called.

## Which versions are affected by CVE-2026-89830?


## How do I fix CVE-2026-89830?

Apply the vendor's patch.

## Is CVE-2026-89830 being exploited?

There is no known exploitation of CVE-2026-89830 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89830 and fix it if it is affected.

What it is: CVE-2026-89830 is a denial of service 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-2026-89830 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-2026-89830/ (Markdown: https://insights.sbomify.com/CVE-2026-89830/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89830
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89830
- OSV: https://osv.dev/vulnerability/CVE-2026-89830

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89830/
Summaries are generated and may contain mistakes; the official description above is the record.