# CVE-2025-68807: block: fix race between wbt_enable_default and IO submission

> A race condition in the Linux kernel block layer can cause hung tasks and denial of service during IO submission.

- **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:** 13 Jan 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-68807, DEBIAN-CVE-2025-68807, GHSA-89m4-pmw6-jxqj, UBUNTU-CVE-2025-68807

## What is CVE-2025-68807?

CVE-2025-68807 is a vulnerability in Linux, published on 13 Jan 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:

block: fix race between wbt_enable_default and IO submission

When wbt_enable_default() is moved out of queue freezing in elevator_change(),
it can cause the wbt inflight counter to become negative (-1), leading to hung
tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter
is in an inconsistent state.

The issue occurs because wbt_enable_default() could race with IO submission,
allowing the counter to be decremented before proper initialization. This manifests
as:

  rq_wait[0]:
    inflight:             -1
    has_waiters:        True

rwb_enabled() checks the state, which can be updated exactly between wbt_wait()
(rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter
will become negative.

And results in hung task warnings like:
  task:kworker/u24:39 state:D stack:0 pid:14767
  Call Trace:
    rq_qos_wait+0xb4/0x150
    wbt_wait+0xa9/0x100
    __rq_qos_throttle+0x24/0x40
    blk_mq_submit_bio+0x672/0x7b0
    ...

Fix this by:

1. Splitting wbt_enable_default() into:
   - __wbt_enable_default(): Returns true if wbt_init() should be called
   - wbt_enable_default(): Wrapper for existing callers (no init)
   - wbt_init_enable_default(): New function that checks and inits WBT

2. Using wbt_init_enable_default() in blk_register_queue() to ensure
   proper initialization during queue registration

3. Move wbt_init() out of wbt_enable_default() which is only for enabling
   disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the
   original lock warning can be avoided.

4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling
   code since it's no longer needed

This ensures WBT is properly initialized before any IO can be submitted,
preventing the counter from going negative.

## Which versions are affected by CVE-2025-68807?


## How do I fix CVE-2025-68807?

Apply the vendor's patch.

## Is CVE-2025-68807 being exploited?

There is no known exploitation of CVE-2025-68807 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68807 and fix it if it is affected.

What it is: CVE-2025-68807 is a vulnerability in Linux, published on 13 Jan 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-2025-68807 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-2025-68807/ (Markdown: https://insights.sbomify.com/CVE-2025-68807/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68807
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68807
- OSV: https://osv.dev/vulnerability/CVE-2025-68807

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68807/
Summaries are generated and may contain mistakes; the official description above is the record.