---
id: "CVE-2026-98820"
kind: "vulnerability"
aliases: ["CVE-2026-98820"]
title: "Linux kernel: block layer request flags can stall the kyber I/O queue"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["block-devices", "infrastructure", "linux-kernel", "self-hosted"]
not_affected_if: ["kyber-not-in-use"]
published_at: "2026-10-18T16:17:36+00:00"
first_seen_at: "2026-10-23T21:57:17+00:00"
updated_at: "2026-10-25T05:14:44+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98820", "first_seen_at": "2026-10-23T21:57:17+00:00"}]
---

# Linux kernel: block layer request flags can stall the kyber I/O queue

In the Linux kernel's block layer, cached requests allocated for passthrough commands can be reused for read or write I/O with the wrong scheduler flags set. For the kyber I/O scheduler this leaks a domain token and stalls the queue; the sources do not say that an attacker can trigger it.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Move to a kernel release that includes the upstream commit titled 'blk-mq: set RQF_USE_SCHED when the operation is known' (the sources do not name a version).

## Timeline

- 2026-10-23T21:57:17+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98820

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

blk-mq: set RQF_USE_SCHED when the operation is known

The cached requests are allocated for one operation but can be handed
out for another. A passthrough command has RQF_USE_SCHED cleared, so
using those flags for a subsequent read/write bio will insert it into
the scheduler without ->prepare_request() and frees it without
->finish_request(). For kyber, this leaks the domain token acquired at
dispatch and stalls the queue.

Don't set RQF_USE_SCHED based on the first operation the batch happened
to be allocated for. Instead, set it after the request is claimed by an
operation. Introduce a helper function, blk_mq_rq_late_init() for this,
and absorb blk_mq_rq_time_init() since the two run together.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_