CVE-2026-99104: sched_ext: Fix the bypass dispatch claim for schedulers bypassed by an ancestor

CVE-2026-99104: sched_ext: Fix the bypass dispatch claim for schedulers bypassed by an ancestor

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-99104 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.1 with commit aa2a0a19686c90106ade6a7e848ffbb62d55d733 and fixed in 7.2.13 with commit f0f18075e45d47bef7ff2eb9512ee4f0c7e5f9c7
	Issue introduced in 7.1 with commit aa2a0a19686c90106ade6a7e848ffbb62d55d733 and fixed in 7.3 with commit 5bdeca322a6f8d10acaf67cccab1f69747ee7be3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-99104
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/sched/ext/ext.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f0f18075e45d47bef7ff2eb9512ee4f0c7e5f9c7
	https://git.kernel.org/stable/c/5bdeca322a6f8d10acaf67cccab1f69747ee7be3