# CVE-2026-89645: btrfs: drop recovered reloc root refs on recovery failure

> A reference counting error in the Linux kernel's Btrfs filesystem can cause memory leaks and potential instability during relocation recovery failures.

- **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:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100844, BELL-CVE-2026-89645, DEBIAN-CVE-2026-89645, GHSA-m8pq-6746-5gfc, UBUNTU-CVE-2026-89645

## What is CVE-2026-89645?

CVE-2026-89645 is a memory corruption vulnerability in Linux, published on 11 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: drop recovered reloc root refs on recovery failure

During relocation recovery, each fs root gets a reference to its relocation
root. If loading or adding a later root fails, or if the first transaction
commit fails, btrfs_recover_relocation() jumps to out_unset before
merge_reloc_roots() and clean_dirty_subvols().

put_reloc_control() drops the list-owned relocation root references, but it
does not clear fs_root->reloc_root or drop the references owned by those
pointers. Mount cleanup only drops them when BTRFS_FS_ERROR is set, so an
error such as -ENOMEM while processing a later root can leave references
behind.

Keep temporary references to the fs roots associated during recovery. On
failure, clear their reloc_root pointers and drop the corresponding
references. Once the first transaction commit succeeds, drop only the
temporary fs root references and let the normal merge and cleanup paths
handle the relocation roots.

Fault injection on a pending-relocation image confirmed the cleanup gap.
With an injected first-commit failure, 25 fs roots had reloc_root set with
fs_error=0. With this fix, the same failure path drops that count to 0
before mount fails.

## Which versions are affected by CVE-2026-89645?


## How do I fix CVE-2026-89645?

Apply the vendor's patch.

## Is CVE-2026-89645 being exploited?

There is no known exploitation of CVE-2026-89645 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89645 and fix it if it is affected.

What it is: CVE-2026-89645 is a memory corruption vulnerability in Linux, published on 11 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-2026-89645 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-2026-89645/ (Markdown: https://insights.sbomify.com/CVE-2026-89645/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89645
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89645
- OSV: https://osv.dev/vulnerability/CVE-2026-89645

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89645/
Summaries are generated and may contain mistakes; the official description above is the record.