---
id: "CVE-2026-99104"
kind: "vulnerability"
aliases: ["CVE-2026-99104"]
title: "Linux kernel: sched_ext bypass dispatch claim leaks, stalling sub-scheduler tasks"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kernel", "linux", "runtime", "sched-ext"]
not_affected_if: []
published_at: "2026-10-28T11:17:29+00:00"
first_seen_at: "2026-10-28T11:32:34+00:00"
updated_at: "2026-10-28T11:37:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99104", "first_seen_at": "2026-10-28T11:32:34+00:00"}]
---

# Linux kernel: sched_ext bypass dispatch claim leaks, stalling sub-scheduler tasks

In the Linux kernel's sched_ext scheduler, a sub-scheduler that is bypassed under an ancestor can keep or never take its bypass dispatch claim, which trips a WARN_ON_ONCE and can leave tasks stuck on bypass queues. The sources describe a reliability and kernel-warning failure rather than a demonstrated way for an attacker to run code.

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

## Timeline

- 2026-10-28T11:32:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99104

## From the sources

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

sched_ext: Fix the bypass dispatch claim for schedulers bypassed by an ancestor

scx_bypass() claims bypass dispatch when the scheduler's depth goes from
zero to one and releases it when the depth returns to zero, but propagates
only the depth to the descendants, not the claim. A descendant that starts
bypassing with its ancestor never claims, and one whose own bypass ends
under the ancestor's keeps its claim, as its depth does not return to zero.

A sub-scheduler enable whose bypass ends under a PM suspend thus leaks its
claim: the parent keeps hosting bypass dispatch and the sub-scheduler's next
bypass trips the WARN_ON_ONCE() on the claim. A sub-scheduler disable that
starts under a PM suspend has no claim, so once the resume lifts the root's
bypass its tasks sit on the parent's bypass DSQs with nobody consuming them.

Claim for every descendant whose depth goes from zero to one in the
propagation and release every scheduler in the subtree whose depth returned
to zero once the tasks have moved out of the bypass DSQs. A parent that is
bypassing itself when a descendant claims consumes only its own bypass DSQs,
empty until it leaves bypass and becomes the host.

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