# CVE-2026-93798: btrfs: fix reloc root cleanup in merge_reloc_roots()

> A race condition in the Linux kernel's Btrfs filesystem could lead to inconsistent state during relocation root cleanup, potentially causing stability issues.

- **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:** 24 Sep 2026
- **Updated:** 3 Oct 2026
- **Also known as:** AZL-103637, BELL-CVE-2026-93798, DEBIAN-CVE-2026-93798, GHSA-9c2v-whhq-6g24, UBUNTU-CVE-2026-93798

## What is CVE-2026-93798?

CVE-2026-93798 is a high-severity vulnerability in Linux, published on 24 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:

btrfs: fix reloc root cleanup in merge_reloc_roots()

If the root we got has zero root refs in its root item, we are resetting
the root's ->reloc_root without using barriers like we do everywhere else.
Sashiko complained about this while reviewing another patch, and it's
correct (see the Link tag below).

Also, we should not clear BTRFS_ROOT_DEAD_RELOC_TREE from the root unless
the root points to the reloc root we have.

Fix this by using clear_reloc_root(), which issues the memory barrier
after setting the root's ->reloc_root to NULL and before clearing the bit
BTRFS_ROOT_DEAD_RELOC_TREE from the root.

## Which versions are affected by CVE-2026-93798?


## How do I fix CVE-2026-93798?

Apply the vendor's patch.

## Is CVE-2026-93798 being exploited?

There is no known exploitation of CVE-2026-93798 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93798 and fix it if it is affected.

What it is: CVE-2026-93798 is a high-severity vulnerability in Linux, published on 24 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-2026-93798 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-2026-93798/ (Markdown: https://insights.sbomify.com/CVE-2026-93798/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93798
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93798
- OSV: https://osv.dev/vulnerability/CVE-2026-93798

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93798/
Summaries are generated and may contain mistakes; the official description above is the record.