# CVE-2026-80855: fuse: fix invalidate lock leak on open O_TRUNC DAX failure

> A local attacker can cause a denial of service in the Linux kernel by triggering a lock leak during a failed DAX truncate operation on a FUSE filesystem.

- **Severity:** Not scored
- **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:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-99474, BELL-CVE-2026-80855, DEBIAN-CVE-2026-80855, GHSA-vqph-p58c-7g7w, UBUNTU-CVE-2026-80855

## What is CVE-2026-80855?

CVE-2026-80855 is a denial of service vulnerability in Linux, published on 4 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:

fuse: fix invalidate lock leak on open O_TRUNC DAX failure

fuse_open() takes filemap_invalidate_lock() for a DAX truncate
(dax_truncate = true) and releases it before the out_inode_unlock
label.  But when fuse_dax_break_layouts() fails, the goto
out_inode_unlock skips the unlock and leaks the rwsem, so any later
fault or truncate on the file stalls on the stale lock.

fuse_dax_break_layouts() can fail with -ERESTARTSYS when a signal
interrupts the wait for busy DAX pages to drain:

  open("file", O_RDWR | O_TRUNC)
  └─ fuse_open()
     ├─ filemap_invalidate_lock()        # dax_truncate
     └─ fuse_dax_break_layouts()
        └─ dax_break_layout()
           └─ wait_page_idle()           # TASK_INTERRUPTIBLE
              └─ fuse_wait_dax_page()    # unlock, schedule, re-lock
                 └─ signal → -ERESTARTSYS
     goto out_inode_unlock               # <- lock leaked

Fix this by moving filemap_invalidate_unlock() below the label so
that all error paths release the lock, and rename the label to
out_unlock as it now covers more than just the inode lock.

## Which versions are affected by CVE-2026-80855?


## How do I fix CVE-2026-80855?

Apply the vendor's patch.

## Is CVE-2026-80855 being exploited?

There is no known exploitation of CVE-2026-80855 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80855 and fix it if it is affected.

What it is: CVE-2026-80855 is a denial of service vulnerability in Linux, published on 4 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-2026-80855 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-2026-80855/ (Markdown: https://insights.sbomify.com/CVE-2026-80855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80855
- OSV: https://osv.dev/vulnerability/CVE-2026-80855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80855/
Summaries are generated and may contain mistakes; the official description above is the record.