Bug 2468235 (CVE-2026-43438)

Summary: CVE-2026-43438 kernel: sched_ext: Remove redundant css_put() in scx_cgroup_init()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's sched_ext component. This vulnerability is caused by a redundant `css_put()` call in the `scx_cgroup_init()` function, leading to a reference count underflow. This can result in a Use-After-Free (UAF) vulnerability, potentially allowing a local attacker to cause a denial of service or achieve privilege escalation.
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Description OSIDB Bzimport 2026-05-08 15:06:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Remove redundant css_put() in scx_cgroup_init()

The iterator css_for_each_descendant_pre() walks the cgroup hierarchy
under cgroup_lock(). It does not increment the reference counts on
yielded css structs.

According to the cgroup documentation, css_put() should only be used
to release a reference obtained via css_get() or css_tryget_online().
Since the iterator does not use either of these to acquire a reference,
calling css_put() in the error path of scx_cgroup_init() causes a
refcount underflow.

Remove the unbalanced css_put() to prevent a potential Use-After-Free
(UAF) vulnerability.
Comment 1 Keith Grant 2026-05-09 00:03:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050853-CVE-2026-43438-f2f2@gregkh/T