CVE-2026-43482: sched_ext: Disable preemption between scx_claim_exit() and kicking helper work

CVE-2026-43482: sched_ext: Disable preemption between scx_claim_exit() and kicking helper work

[Greg Kroah-Hartman]

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

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

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

sched_ext: Disable preemption between scx_claim_exit() and kicking helper work

scx_claim_exit() atomically sets exit_kind, which prevents scx_error() from
triggering further error handling. After claiming exit, the caller must kick
the helper kthread work which initiates bypass mode and teardown.

If the calling task gets preempted between claiming exit and kicking the
helper work, and the BPF scheduler fails to schedule it back (since error
handling is now disabled), the helper work is never queued, bypass mode
never activates, tasks stop being dispatched, and the system wedges.

Disable preemption across scx_claim_exit() and the subsequent work kicking
in all callers - scx_disable() and scx_vexit(). Add
lockdep_assert_preemption_disabled() to scx_claim_exit() to enforce the
requirement.

The Linux kernel CVE team has assigned CVE-2026-43482 to this issue.


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

	Issue introduced in 6.12 with commit f0e1a0643a59bf1f922fa209cec86a170b784f3f and fixed in 6.12.78 with commit 41423912f7ac7494ccd6eef411227b4efce740e0
	Issue introduced in 6.12 with commit f0e1a0643a59bf1f922fa209cec86a170b784f3f and fixed in 6.18.20 with commit 522acaae34aa7e05859260056b39c7c030592a0c
	Issue introduced in 6.12 with commit f0e1a0643a59bf1f922fa209cec86a170b784f3f and fixed in 6.19.9 with commit 5131dbec2c10961b34f844bc30b400c3fa0bcc72
	Issue introduced in 6.12 with commit f0e1a0643a59bf1f922fa209cec86a170b784f3f and fixed in 7.0 with commit 83236b2e43dba00bee5b82eb5758816b1a674f6a

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-2026-43482
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.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/41423912f7ac7494ccd6eef411227b4efce740e0
	https://git.kernel.org/stable/c/522acaae34aa7e05859260056b39c7c030592a0c
	https://git.kernel.org/stable/c/5131dbec2c10961b34f844bc30b400c3fa0bcc72
	https://git.kernel.org/stable/c/83236b2e43dba00bee5b82eb5758816b1a674f6a