# CVE-2026-98079: btrfs: zstd: fix lost wakeup when waiting for a workspace

> A race condition in the Linux kernel's btrfs zstd compression can cause writers to hang indefinitely, leading to a local 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:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-104858, BELL-CVE-2026-98079, DEBIAN-CVE-2026-98079, GHSA-4xrv-jf38-655f, UBUNTU-CVE-2026-98079

## What is CVE-2026-98079?

CVE-2026-98079 is a vulnerability in Linux, published on 25 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: zstd: fix lost wakeup when waiting for a workspace

A writer can sleep forever in zstd_get_workspace() even though a workspace
is free.  When zstd_alloc_workspace() fails, the task is queued on
zwsm->wait and schedules unconditionally, never re-testing the pool.
zstd_put_workspace() publishes the workspace and then calls cond_wake_up(),
which only wakes when a sleeper is already visible, so a workspace returned
between the failed allocation and prepare_to_wait() wakes nobody.  The
window is wide: zstd_alloc_workspace() goes through kvmalloc() and may
enter reclaim.

Only a max level workspace triggers the wakeup and one is deliberately kept
allocated as the fallback every waiter waits for, so once its wakeup is
lost the writer stays in TASK_UNINTERRUPTIBLE until some other task happens
to return one.  Re-check the pool after prepare_to_wait() has published the
waiter, and use the workspace if one turned up.

## Which versions are affected by CVE-2026-98079?


## How do I fix CVE-2026-98079?

Apply the vendor's patch.

## Is CVE-2026-98079 being exploited?

There is no known exploitation of CVE-2026-98079 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98079 and fix it if it is affected.

What it is: CVE-2026-98079 is a vulnerability in Linux, published on 25 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-2026-98079 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-2026-98079/ (Markdown: https://insights.sbomify.com/CVE-2026-98079/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98079
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98079
- OSV: https://osv.dev/vulnerability/CVE-2026-98079

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98079/
Summaries are generated and may contain mistakes; the official description above is the record.