* [CVE-2026-98542][MODERATE REGULAR] cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict [ Upstream
@ 2026-10-24 7:01 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 7:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98542
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict [ Upstream
Commit: 241e67b60308cdce25bba66616a109759edd1d40
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=241e67b60308cdce25bba66616a109759edd1d40
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98542
Analysis date: Sat, 24 Oct 2026 03:01:33 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Important candidate requiring manual review
Manual review required: YES
Summary:
A missing cpuset conflict rejection permits two active root partitions to claim the same exclusive CPU, leaving kernel scheduling state inconsistent across an unresolved delegation boundary.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98542 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98542
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: MODERATE REGULAR
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98542 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98542 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';*CWE-20;CWE-703;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '4.4';DESCR 'A cpuset state validation regression lets remote_partition_enable accept a remote partition whose CPUs overlap subpartitions_cpus already owned by an ancestor local partition. This breaks exclusive CPU ownership and leaves two active root partitions claiming the same CPU. The demonstrated primitive is a WARN and inconsistent cpuset partition state. There is no evidence of UAF, OOB access, or other memory corruption. For the CVSS the PR:H base case reflects host level cpuset administration. For the CVSS the PR:L worst case reflects delegated cgroup administration where a less privileged container or service can create the shown hierarchy. The issue is local and may cause limited integrity and availability impact through broken CPU isolation or workload interference, but a kernel panic or host wide denial of service is not established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 3 with recommendation Actionable Moderate / Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage LOW to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 2.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';NO MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Important candidate requiring manual review (with actual score 3) MAYBE WARNONLY HARDWARE LINUS TEST INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; unknown delegated reachability was not converted into a bonus.
* Final recommended bucket: **Actionable Moderate / Important candidate requiring manual review**::
2. Signal breakdown
* +1 — Active structured-state corruption: a failed `subpartitions_cpus` conflict check was reduced to `WARN_ON_ONCE()`, after which the remote partition was enabled with CPUs already exclusively owned by an ancestor partition.
* +1 — Integrity impact: the demonstrated result is two active root partitions claiming exclusive ownership of CPU 1.
* +1 — Privileged downstream consumption: the conflicting cpuset partition and CPU-ownership state remains active for later cpuset/scheduler enforcement rather than being rejected or merely diagnosed.
* No negative privilege point: host-admin-only triggering is not positively established.
* No crash/availability point: only a warning and inconsistent ownership state are demonstrated.
* No UAF, OOB access, arbitrary write, disclosure, authorization bypass, or privilege escalation is shown.
* B5-R and B3-PENDING do not apply: there is no heap OOB write or shared-backing write.
* B4-PENDING does not apply: this is an invariant-validation failure, not a mandatory authorization guard changing DENY to ALLOW.
3. Reachability analysis
The reproducer mounts cgroup2 and configures cpuset partition hierarchy files, operations commonly associated with privileged cgroup administration. The supplied evidence does not establish whether the complete sequence requires host administration or works through delegated cgroup/cpuset control below host admin. Consequently, both host-admin and namespace-scoped privilege remain unknown.
No race, special hardware, boot mode, or retry sequence is required. The hierarchy and conflict are deliberately constructed, but any required prior delegation is unresolved.
4. Primitive and severity reading
The exact primitive is attacker-influenced corruption of active cpuset ownership state: `remote_partition_enable()` proceeds after detecting an overlap and installs a second active partition claim. This is CLASS_B structured-state corruption, not kernel memory corruption.
The later consumer is normal kernel cpuset/scheduling enforcement operating on the conflicting active ownership state. A credible delegated-cgroup or container/service-to-host resource-isolation boundary exists, but the patch does not prove that a below-host-admin actor can perform the complete trigger. Thus cross-boundary workload interference remains unresolved rather than demonstrated.
ImportantCandidate is YES under the active-state/trust-boundary review rule. Auto-downgrade is disallowed because the write to active ownership state, its privileged consumer, and the unresolved delegation boundary form a concrete integrity-review chain. This is not proof of panic, LPE, or Important severity.
5. One-sentence report phrase
A missing cpuset conflict rejection permits two active root partitions to claim the same exclusive CPU, leaving kernel scheduling state inconsistent across an unresolved delegation boundary.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm cgroup delegation and namespace capability requirements, and determine whether conflicting ownership permits cross-tenant CPU-isolation or workload interference.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict [ Upstream
Commit: 241e67b60308cdce25bba66616a109759edd1d40
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=241e67b60308cdce25bba66616a109759edd1d40
Changed files:
tools/testing/selftests/cgroup/test_cpuset_prs.sh.
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=241e67b60308cdce25bba66616a109759edd1d40
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98542 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98542
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS score: 4.4
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 3
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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