[CVE-2026-93112][IMPORTANT] bpf: Require a BPF cpumask for bpf_cpumask_populate() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-93112
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Require a BPF cpumask for bpf_cpumask_populate() [ Upstream
Commit: 0cfc9348a045da64955af2dd6902e66dfc7d6469
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cfc9348a045da64955af2dd6902e66dfc7d6469
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93112
Analysis date: Thu, 17 Sep 2026 17:45:57 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-93112 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93112

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: IMPORTANT
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-2026-93112	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-93112 CHECK WITH IMPACT FROM ORIG NN 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:H/I:H/A:H';CWE-284;CWE-863;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '7.8';DESCR 'bpf_cpumask_populate accepted a generic struct cpumask destination even though it writes to that destination with bitmap_copy. This allowed the BPF verifier to treat borrowed read-only cpumask pointers returned by query kfuncs such as scx_bpf_get_online_cpumask as valid writable destinations. A local attacker able to load and run a relevant BPF or sched_ext program could corrupt kernel owned cpumask state and potentially crash the system or affect scheduler and CPU mask integrity. For the CVSS the PR:L is used in the paranoid score because reduced BPF capable users, service accounts, container root, or delegated CAP_BPF/CAP_SYS_ADMIN contexts may be enough in some deployments. The issue is not network reachable. Impact is at least local denial of service or kernel state corruption and in worst case may allow confidentiality or integrity impact due to a write into kernel owned state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)  SKIP CVE-2026-93112 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	BPF SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor applied. BPF privileged control-plane cap does not reduce it below 5.
* Raw paranoid score: 6
* Paranoid score: 6. No floor applied. BPF privileged control-plane cap is consistent with 6.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2: Concrete BPF verifier ownership and mutability boundary bypass. The kfunc accepted `struct cpumask *` even though it mutates the destination, allowing borrowed read-only cpumask pointers from query kfuncs to be accepted as writable.
* +2: Controlled kernel-state overwrite primitive. `bitmap_copy()` copies attacker-provided BPF memory into the destination cpumask bits, and the destination may be a kernel-owned borrowed cpumask rather than an owned `struct bpf_cpumask`.
* +1: Integrity impact is plausible. The primitive can modify protected scheduler or cpumask state that should not be writable by that BPF program path.
* Paranoid additional +1: Availability impact is plausible because corruption of active cpumask or scheduler-related masks may destabilize scheduling or CPU selection, even though a specific crash trace is not supplied.

Negative or non-awarded signals:

* 0: RealUAF is not established.
* 0: No repeated release/refcount operation exists.
* 0: Controlled reclaim, arbitrary kernel read/write, callback control, credential overwrite, or demonstrated LPE is not established.
* 0: Remote reachability is not established.
* 0: Local ordinary unprivileged trigger is not awarded because BPF and sched_ext loading/attachment privilege is unresolved and usually privilege-gated.
* 0: Host-admin penalty is not applied because full host-admin-equivalent privilege is not positively established from the supplied input.
* 0: Namespace-scoped privilege is not awarded because the complete BPF load, attach, and trigger chain is not shown to be namespace-scoped.
* 0: Reliable kernel crash is not awarded conservatively because the patch establishes writable kernel-state corruption, not a concrete panic trace.
* 0: Confidentiality is not awarded conservatively because no disclosure path is shown.

Repeated release/refcount checklist:

* First release can end lifetime: not applicable.
* Exact same reference survives: not applicable.
* Second operation mutates lifetime/refcount: not applicable.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied for repeated release: no.

3. Reachability analysis

The attacker needs the ability to load and run a relevant BPF or sched_ext program that can call `bpf_cpumask_populate()` and obtain a borrowed cpumask from a read-only query kfunc such as `scx_bpf_get_online_cpumask()`.

BPF and sched_ext operations are commonly privilege-gated by CAP_BPF, CAP_SYS_ADMIN, or other administrative setup, but the supplied input does not fully establish whether the complete trigger requires host-admin-equivalent privilege in the evaluated product. Therefore HostAdminRequired is UNKNOWN rather than YES.

NamespaceScopedPrivilege is UNKNOWN. The patch does not establish that all required stages, including BPF program load, kfunc availability, sched_ext use, and attachment, can be completed with only attacker-obtainable namespace-scoped capabilities.

Prior host setup may be required if sched_ext or BPF policy is restricted, but the exact deployment dependency is not fully resolved from the input. No network trigger, special hardware, or race timing is involved. The issue is deterministic once the relevant BPF program can call the kfunc with a borrowed read-only cpumask destination.

4. Primitive and severity interpretation

The exact primitive is a verifier-enforced ownership and mutability failure: a mutating cpumask kfunc accepted a generic `struct cpumask *` destination, so read-only borrowed cpumask objects could be passed to a function that writes through `bitmap_copy()`.

This is not UAF and not fixed stale storage. It is an active kernel-state corruption primitive because the object being modified is an active cpumask used by scheduler or CPU mask logic. The patch changes the destination type to `struct bpf_cpumask *`, restoring the intended rule that mutating cpumask kfuncs require an owned BPF cpumask.

PrimitiveClass is CLASS_A because the patch establishes a controlled write into kernel-owned state through a verifier permission and ownership bypass. The demonstrated consequence is unauthorized modification of protected cpumask state. The speculative consequence is broader scheduler disruption or possible privilege-relevant kernel state manipulation, but no full LPE chain is supplied.

ImportantCandidate is YES because this is not a simple crash-only bug. It is a concrete BPF verifier boundary failure with a writable kernel-state primitive. AutoDowngradeAllowed is NO because automatically treating this as ordinary Moderate would lose a meaningful kernel ownership and mutability bypass that requires manual review.

Likely operational severity is at least Actionable Moderate. It may be an Important candidate depending on the exact BPF privilege model and which borrowed cpumask objects are reachable in the affected kernel configuration.

5. One-sentence report phrase

`bpf_cpumask_populate()` allowed a mutating `bitmap_copy()` operation on borrowed read-only cpumask objects, enabling a privileged or delegated BPF attacker to corrupt kernel-owned cpumask state and requiring manual review of scheduler and BPF boundary impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete BPF verifier ownership and mutability bypass with a controlled write into kernel-owned cpumask state, while the complete privilege boundary and downstream impact are not fully resolved.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: bpf: Require a BPF cpumask for bpf_cpumask_populate() [ Upstream
Commit: 0cfc9348a045da64955af2dd6902e66dfc7d6469
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cfc9348a045da64955af2dd6902e66dfc7d6469

Changed files:
  kernel/bpf/cpumask.c
  tools/sched_ext/include/scx/compat.bpf.h

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=0cfc9348a045da64955af2dd6902e66dfc7d6469

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-93112 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93112

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:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 6

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).