[CVE-2026-99124][MODERATE REGULAR] s390/pci: Fix leak of uninitialized kernel data in SCLP report

[CVE-2026-99124][MODERATE REGULAR] s390/pci: Fix leak of uninitialized kernel data in SCLP report

[AL-KERNEL]

CVE: CVE-2026-99124
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/pci: Fix leak of uninitialized kernel data in SCLP report
Commit: ba5001db9bb23ff7d2ea328c405c287ffb07786f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba5001db9bb23ff7d2ea328c405c287ffb07786f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99124
Analysis date: Fri, 30 Oct 2026 10:46:32 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An insufficient length check allowed a privileged sysfs writer to make the s390 SCLP report path read adjacent heap data, without a demonstrated lower-authority disclosure or corruption effect.

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

The original Linux kernel CVE announcement for CVE-2026-99124 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99124

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-99124	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99124 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-125;CWE-130;*CWE-20;*CWE-200;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'The s390 PCI report_error sysfs handler validated only that the input contained the report header. It did not verify that the supplied buffer also contained the payload size claimed by report length. This allowed sclp_pci_report to read beyond the kmalloc buffer and include up to around 4 KB of adjacent kernel data in a malformed SCLP report. For the CVSS the PR:H value reflects that direct writes to this sysfs control are normally restricted to root or an equivalent privileged management process. The paranoid PR:L interpretation applies only where this operation is delegated to a reduced capability service account. The SCLP processing entity is privileged and can already access at least the page containing the report, while the writer does not receive the copied data. Therefore the concrete primitive is an out of bounds read but attacker usable disclosure, memory corruption, privilege escalation, and availability impact are not established. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 3.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC 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 LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 2.8 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	WRITE OOB SIMPLEFIX LEAK HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1; delegation and attacker-visible disclosure are not proven.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* **+1 — Limited heap out-of-bounds read:** attacker-supplied `report->length` can exceed the actual sysfs write buffer, causing `sclp_pci_report()` to read up to roughly 4 KiB beyond the `kmalloc(len + 1)` allocation.
* **+0 — Confidentiality:** the bytes go to the privileged SCLP-processing entity, which the commit says can already access at least the containing page. No read-back to the writer or lower-authority recipient is shown.
* **+0 — Availability/integrity:** no write, panic, persistent corruption, or malformed-report consequence beyond rejection-worthy input is established.
* No UAF, authorization bypass, controlled write, B5-R retry accumulation, B3 shared-backing write, or protected-resource access is shown.

3. Reachability analysis

The trigger is a write to the s390 PCI `report_error` sysfs attribute with a valid header but an inflated payload length. The supplied hints say this interface is normally restricted to root or an equivalent management process, but the visible patch does not establish exact mode bits, capability checks, delegation, or the complete credential boundary. Therefore host-admin, UID 0, and namespace scope remain unknown rather than assumed. No race or retry sequence is required.

4. Primitive and severity reading

The exact primitive is a bounded heap OOB read passed into an SCLP report. It is read-only and does not expose data back to the writer; the documented recipient already has access to the relevant memory. This supports CLASS_C rather than an exploitable corruption primitive. Stronger disclosure, LPE, kernel write, or crash effects are unproven. ImportantCandidate is NO and automatic Moderate downgrade remains permissible.

5. One-sentence report phrase

An insufficient length check allowed a privileged sysfs writer to make the s390 SCLP report path read adjacent heap data, without a demonstrated lower-authority disclosure or corruption effect.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm the sysfs permissions and whether any deployment delegates this attribute to an entity lacking equivalent SCLP memory access.

7. Call-site confidence

Call-site confidence: high

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

Patch: s390/pci: Fix leak of uninitialized kernel data in SCLP report
Commit: ba5001db9bb23ff7d2ea328c405c287ffb07786f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba5001db9bb23ff7d2ea328c405c287ffb07786f

Commit description:

While report_error_write() checks that the provided buffer is at least
as large as the header struct, but not that it is large enough to
contain the report with the length claimed by report->length. If
user-space provides a short buffer, meaning a larger report->length than
the actually written payload, up to around 4K of kernel data from past
the kmalloc(len + 1) sized buffer allocated in kernfs_fop_write_iter()
will leak into the SCLP report.

However, as the entity processing the SCLP is privileged and able to
access at least the page including the report, this does not leak data
that entity could not access but it is still an out of bounds read and
a malformed error report that should be rejected.

Fixes: 368704a ("s390/pci: add report_error attribute")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/s390/pci/pci_sysfs.c

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=ba5001db9bb23ff7d2ea328c405c287ffb07786f

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

The original Linux kernel CVE announcement for CVE-2026-99124 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99124

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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: 1

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