# CVE-2026-89578: dm-io: clone the source bio instead of copying its biovec

> A local attacker can cause a system hang in the Linux kernel by triggering a loop in dm-io during misaligned direct I/O operations.

- **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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89578, DEBIAN-CVE-2026-89578, GHSA-36gx-2j3f-6gcr, UBUNTU-CVE-2026-89578

## What is CVE-2026-89578?

CVE-2026-89578 is a denial of service 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:

dm-io: clone the source bio instead of copying its biovec

For DM_IO_BIO requests, do_region() built each destination bio by walking
the source bio's biovec and re-adding the pages one at a time, tracking
the remaining transfer in sectors. The vector lengths are byte granular
and need not be sector aligned (e.g. a misaligned O_DIRECT buffer split
across pages), so the sector-based accounting could lose a sub-sector
fragment: to_sector() truncated the remainder and the outer loop spun
forever submitting empty bios, hanging the I/O.

There is no need to rebuild the biovec at all. The destination reads into
(or writes from) exactly the same pages as the source bio, so the bio can
simply clone the source's biovec with bio_alloc_clone() and remap it to
the target device. The clone inherits the source's iterator and alignment,
and the block layer splits it to the target's limits on submission, so the
whole region maps to a single cloned bio with no manual page copying or
sector accounting.

This removes the per-page copy path (and its open-coded bvec dpages
helpers) for bio-backed I/O and fixes the hang on misaligned direct I/O to
a dm-mirror device. Page-list, vma and kmem sources keep the existing copy
path.

## Which versions are affected by CVE-2026-89578?


## How do I fix CVE-2026-89578?

Apply the vendor's patch.

## Is CVE-2026-89578 being exploited?

There is no known exploitation of CVE-2026-89578 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89578 and fix it if it is affected.

What it is: CVE-2026-89578 is a denial of service 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-2026-89578 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-2026-89578/ (Markdown: https://insights.sbomify.com/CVE-2026-89578/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89578
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89578
- OSV: https://osv.dev/vulnerability/CVE-2026-89578

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89578/
Summaries are generated and may contain mistakes; the official description above is the record.