# CVE-2026-93781: scsi: core: Do not block on tag allocation in scsi_eh_lock_door()

> A deadlock in the Linux kernel SCSI error handler can cause a denial of service by blocking I/O operations when tags are exhausted.

- **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:** 24 Sep 2026
- **Updated:** 3 Oct 2026
- **Also known as:** AZL-103550, BELL-CVE-2026-93781, DEBIAN-CVE-2026-93781, GHSA-3mhv-m8g9-8q53, UBUNTU-CVE-2026-93781

## What is CVE-2026-93781?

CVE-2026-93781 is a denial of service vulnerability in Linux, published on 24 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:

scsi: core: Do not block on tag allocation in scsi_eh_lock_door()

scsi_eh_lock_door() is called from scsi_restart_operations() while the
host is still in the SHOST_RECOVERY state, i.e. before the host is
switched back to SHOST_RUNNING and scsi_run_host_queues() restarts the
queues. It allocates a request via scsi_alloc_request() with no flags,
so blk_mq_get_tag() may block waiting for a free sched tag when all tags
are already in use.

Those tags can be held by commands that were just requeued by
scsi_eh_flush_done_q() during error handling. Such commands cannot be
dispatched until the host leaves SHOST_RECOVERY and
scsi_run_host_queues() is called - which only happens *after*
scsi_eh_lock_door() returns.

This forms a circular dependency:

  - scsi_eh_lock_door(), running in the SCSI error handler thread, waits
    for a sched tag held by a requeued command;

  - the requeued command cannot complete and release its sched tag until
    the error handler thread leaves scsi_restart_operations() and restart
    the queues.

For devices with a single driver tag (e.g. USB storage) it is a
guaranteed deadlock and I/O that can never be submitted. This problem
has also been reproduced in our environment.

Locking the door is a best-effort operation, and scsi_eh_lock_door()
already returns silently when the request allocation fails. Pass
BLK_MQ_REQ_NOWAIT to scsi_alloc_request() so the allocation fails
instead of blocking when no tag is available. This breaks the circular
dependency and allows the error handler to finish restarting the queues,
after which the pending commands are dispatched normally.

## Which versions are affected by CVE-2026-93781?


## How do I fix CVE-2026-93781?

Apply the vendor's patch.

## Is CVE-2026-93781 being exploited?

There is no known exploitation of CVE-2026-93781 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93781 and fix it if it is affected.

What it is: CVE-2026-93781 is a denial of service vulnerability in Linux, published on 24 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-2026-93781 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-2026-93781/ (Markdown: https://insights.sbomify.com/CVE-2026-93781/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93781
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93781
- OSV: https://osv.dev/vulnerability/CVE-2026-93781

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93781/
Summaries are generated and may contain mistakes; the official description above is the record.