# GSD-2021-1002438: net: vlan: fix underflow for the real_dev refcnt

> An integer underflow in the Linux Kernel VLAN driver can lead to a reference count error, potentially causing a 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:** No
- **Published:** 19 Dec 2021

## What is GSD-2021-1002438?

GSD-2021-1002438 is a vulnerability in Kernel, published on 19 Dec 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

net: vlan: fix underflow for the real_dev refcnt

This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven.
This ID is fixed in Linux Kernel version v5.4.163 by commit 5e44178864b38dd70b877985abd7d86fdb95f27d, it was introduced in version v5.4.160 by commit 700602b662d7eaa816b1a3cb0abe7a85de358fd4. For more details please see the references link.

## Which versions are affected by GSD-2021-1002438?

1 open source package ship an affected version, including Kernel.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Kernel` | Linux | All versions | None |

## How do I fix GSD-2021-1002438?

No fix has been published for GSD-2021-1002438 yet. Limit exposure of the affected software until one is available.

## Is GSD-2021-1002438 being exploited?

There is no known exploitation of GSD-2021-1002438 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GSD-2021-1002438 and fix it if it is affected.

What it is: GSD-2021-1002438 is a vulnerability in Kernel, published on 19 Dec 2021. 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 GSD-2021-1002438 in the wild and no public exploit code.

Affected packages and fixed versions:
- Kernel (Linux): affected all versions; no fix listed

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/GSD-2021-1002438/ (Markdown: https://insights.sbomify.com/GSD-2021-1002438/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GSD-2021-1002438

---
From sbomify Insights: https://insights.sbomify.com/GSD-2021-1002438/
Summaries are generated and may contain mistakes; the official description above is the record.