[CVE-2026-80552][MODERATE 7.0] s390/vfio_ccw: Ensure index for read/write regions are within range

[CVE-2026-80552][MODERATE 7.0] s390/vfio_ccw: Ensure index for read/write regions are within range

[AL-KERNEL]

CVE: CVE-2026-80552
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/vfio_ccw: Ensure index for read/write regions are within range
Commit: d3b1e38404b22df5a1f93019f2bb656feaad5ae3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d3b1e38404b22df5a1f93019f2bb656feaad5ae3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80552
Analysis date: Wed, 26 Aug 2026 13:14:37 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
`s390 vfio_ccw failed to validate read and write region indexes against num_regions, allowing a local process with VFIO device access to reach out of bounds region entries and potentially trigger a kernel crash, information exposure, or constrained kernel memory corruption.`

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

The original Linux kernel CVE announcement for CVE-2026-80552 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80552

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 7.0
Manual review required: YES

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

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80552	MODERATE	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-129;CWE-125;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 's390 vfio_ccw did not fully enforce bounds checks for existing read and write region indexes. A local process with access to the vfio_ccw device interface could select an out of range region index and reach private region array access outside the valid num_regions range. This can cause invalid reads, invalid writes, NULL pointer dereference, or use of an unintended region ops pointer depending on adjacent memory layout. For the CVSS the PR:L is used in the paranoid score because reliable triggering requires local code execution with access to the VFIO device fd, but that access may be delegated to a reduced capability VM process or service account rather than full host root. The issue is not network reachable and is not directly triggered by packet traffic. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to out of bounds region access and possible memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	SIMPLEFIX LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Weak/indirect corruption candidate: +1**. The region index can be outside `private->num_regions`, leading to out-of-bounds access to `private->region[index]`.
* **Weak LPE concern: +1**. The bug can select an unintended `region` entry and then use its `ops` or `data` fields. This is not a demonstrated arbitrary write, but it is more than a pure NULL dereference.
* **Reliable kernel crash / strong DoS: +1**. Invalid `region[index].ops`, `region[index].data`, or bogus handler dispatch can realistically crash the kernel.
* **Confidentiality impact plausible: +1**. The read paths use `copy_to_user()` from `region->data`; if the out-of-bounds entry resolves to a valid unintended pointer, limited kernel or adjacent object data exposure is plausible.
* **Integrity impact plausible: +1**. The write paths use `copy_from_user()` into `region->data`; if the out-of-bounds entry resolves to a valid unintended pointer, constrained kernel memory corruption is plausible.
* **Privileged kernel/device-management memory corruption path: +1**. This is in the VFIO mediated device path, a trusted kernel device-management interface.
* **Requires admin/root/CAP-level setup in typical deployments: -2**. Creating and assigning `vfio_ccw` mediated devices is usually administrator-controlled.
* **Rare AND difficult-to-reach subsystem/configuration: -1**. This is s390-specific and requires `vfio_ccw` mediated-device usage.

Paranoid additions/interpretation:

* **Local reduced-privilege trigger: +1**. In realistic virtualization deployments, the triggering process may be QEMU or a service account with a delegated VFIO fd, not full host root.
* **Availability impact realistic: +1**. A host-wide crash from a delegated VFIO device fd is operationally significant and potentially repeatable.

## 3. Reachability analysis

The bug is locally reachable through the `vfio_ccw` mediated-device read/write/ioctl interface on s390 systems. A fully unprivileged local user normally cannot create or access this device path, but a reduced-privilege VM process or service account may receive an already-open VFIO device fd after administrator setup. Containers and namespaces do not usually make this broadly unprivileged, but delegated device access can reduce the practical privilege requirement from full host root to a confined local process.

This is not network reachable and is not triggered by guest packet traffic. Exploitation requires an s390 host using `vfio_ccw` mediated devices and access to the affected VFIO interface.

Call-site confidence: **high**, because the patch shows both the top-level `vfio_ccw_mdev_read/write()` dispatch and the affected region handlers.

## 4. Severity interpretation

This is stronger than an ordinary Moderate validation bug because the unchecked index can affect object selection, handler dispatch, and user copy source or destination pointers. The realistic evidence supports local DoS and plausible limited OOB read/write effects. A full privilege-escalation primitive is not demonstrated, but the VFIO object context and write path justify manual review.

Conservatively this is a borderline manual-review issue. Paranoid triage should treat it as an Important candidate because delegated VFIO fd access plus out-of-bounds region selection can plausibly cross from crash into kernel memory corruption.

## 5. One-sentence report phrase

`s390 vfio_ccw failed to validate read and write region indexes against num_regions, allowing a local process with VFIO device access to reach out of bounds region entries and potentially trigger a kernel crash, information exposure, or constrained kernel memory corruption.`

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the patch fixes an unchecked array index in a VFIO userspace interface, with both read and write paths reaching out-of-bounds region metadata and possible unintended `ops` or `data` pointer use.

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

Patch: s390/vfio_ccw: Ensure index for read/write regions are within range
Commit: d3b1e38404b22df5a1f93019f2bb656feaad5ae3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d3b1e38404b22df5a1f93019f2bb656feaad5ae3

Commit description:

The introduction of the capability chain rightly clamped the
region indexes to the range of the capabilities itself, but
neglected to do so for the existing read/write regions which
should also be enforced.

Fixes: db8e5d1 ("vfio-ccw: add capabilities chain")
Cc: stable@vger.kernel.org
Cc: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/cio/vfio_ccw_async.c
  drivers/s390/cio/vfio_ccw_chp.c
  drivers/s390/cio/vfio_ccw_ops.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=d3b1e38404b22df5a1f93019f2bb656feaad5ae3

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

The original Linux kernel CVE announcement for CVE-2026-80552 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80552

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:L/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: 4
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).