From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-43392: sched_ext: Fix starvation of scx_enable() under fair-class saturation
Date: Fri, 8 May 2026 16:22:01 +0200 [thread overview]
Message-ID: <2026050837-CVE-2026-43392-00ee@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
sched_ext: Fix starvation of scx_enable() under fair-class saturation
During scx_enable(), the READY -> ENABLED task switching loop changes the
calling thread's sched_class from fair to ext. Since fair has higher
priority than ext, saturating fair-class workloads can indefinitely starve
the enable thread, hanging the system. This was introduced when the enable
path switched from preempt_disable() to scx_bypass() which doesn't protect
against fair-class starvation. Note that the original preempt_disable()
protection wasn't complete either - in partial switch modes, the calling
thread could still be starved after preempt_enable() as it may have been
switched to ext class.
Fix it by offloading the enable body to a dedicated system-wide RT
(SCHED_FIFO) kthread which cannot be starved by either fair or ext class
tasks. scx_enable() lazily creates the kthread on first use and passes the
ops pointer through a struct scx_enable_cmd containing the kthread_work,
then synchronously waits for completion.
The workfn runs on a different kthread from sch->helper (which runs
disable_work), so it can safely flush disable_work on the error path
without deadlock.
The Linux kernel CVE team has assigned CVE-2026-43392 to this issue.
Affected and fixed versions
===========================
Issue introduced in 6.12 with commit 8c2090c504e998c8f34ec870bae71dafcc96a6e0 and fixed in 6.12.78 with commit e0b14bf06393be137d3efb6a3b7cd5b4b9810a6b
Issue introduced in 6.12 with commit 8c2090c504e998c8f34ec870bae71dafcc96a6e0 and fixed in 6.18.20 with commit c44198f25fdfecc0ec0fe366bf8a47fe17d8e229
Issue introduced in 6.12 with commit 8c2090c504e998c8f34ec870bae71dafcc96a6e0 and fixed in 6.19.9 with commit 05ab9ec5dc24f234e0a2fecf3e6ff937c68f7d81
Issue introduced in 6.12 with commit 8c2090c504e998c8f34ec870bae71dafcc96a6e0 and fixed in 7.0 with commit b06ccbabe2506fd70b9167a644978b049150224a
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-2026-43392
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/e0b14bf06393be137d3efb6a3b7cd5b4b9810a6b
https://git.kernel.org/stable/c/c44198f25fdfecc0ec0fe366bf8a47fe17d8e229
https://git.kernel.org/stable/c/05ab9ec5dc24f234e0a2fecf3e6ff937c68f7d81
https://git.kernel.org/stable/c/b06ccbabe2506fd70b9167a644978b049150224a
reply other threads:[~2026-05-08 14:25 UTC|newest]
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