# CVE-2021-46942: io_uring: fix shared sqpoll cancellation hangs

> A flaw in the Linux kernel's io_uring subsystem causes shared sqpoll cancellation hangs, leading to a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** No
- **Published:** 27 Feb 2024
- **Updated:** 11 May 2026
- **Also known as:** GHSA-rhmj-w54j-qcf6, UBUNTU-CVE-2021-46942

## What is CVE-2021-46942?

CVE-2021-46942 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 2024. 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:

io_uring: fix shared sqpoll cancellation hangs

[  736.982891] INFO: task iou-sqp-4294:4295 blocked for more than 122 seconds.
[  736.982897] Call Trace:
[  736.982901]  schedule+0x68/0xe0
[  736.982903]  io_uring_cancel_sqpoll+0xdb/0x110
[  736.982908]  io_sqpoll_cancel_cb+0x24/0x30
[  736.982911]  io_run_task_work_head+0x28/0x50
[  736.982913]  io_sq_thread+0x4e3/0x720

We call io_uring_cancel_sqpoll() one by one for each ctx either in
sq_thread() itself or via task works, and it's intended to cancel all
requests of a specified context. However the function uses per-task
counters to track the number of inflight requests, so it counts more
requests than available via currect io_uring ctx and goes to sleep for
them to appear (e.g. from IRQ), that will never happen.

Cancel a bit more than before, i.e. all ctxs that share sqpoll
and continue to use shared counters. Don't forget that we should not
remove ctx from the list before running that task_work sqpoll-cancel,
otherwise the function wouldn't be able to find the context and will
hang.

## Which versions are affected by CVE-2021-46942?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46942?

No fix has been published for CVE-2021-46942 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-46942 being exploited?

There is no known exploitation of CVE-2021-46942 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-46942 and fix it if it is affected.

What it is: CVE-2021-46942 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 2024. 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-2021-46942 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2021-46942/ (Markdown: https://insights.sbomify.com/CVE-2021-46942/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46942
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46942
- OSV: https://osv.dev/vulnerability/CVE-2021-46942

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46942/
Summaries are generated and may contain mistakes; the official description above is the record.