[CVE-2026-46161][LOW] md/raid10: fix divide-by-zero in setup_geo() with zero far_copies

[CVE-2026-46161][LOW] md/raid10: fix divide-by-zero in setup_geo() with zero far_copies

[AL-KERNEL]

CVE: CVE-2026-46161
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: md/raid10: fix divide-by-zero in setup_geo() with zero far_copies
Commit: 4af2e558e6fdfb972c61350653fd55d1f62b60a5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4af2e558e6fdfb972c61350653fd55d1f62b60a5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46161
Analysis date: Thu, 28 May 2026 06:03:04 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A crafted MD RAID10 layout with zero `near_copies` or `far_copies` can trigger a divide-by-zero in `setup_geo()`, causing a privileged local denial of service during array setup.

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

The original Linux kernel CVE announcement for CVE-2026-46161 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46161

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: LOW
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-2026-46161	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-369;*CWE-20;CWE-754;BEST CVSS score: '4.4';DESCR 'md raid10 setup_geo did not reject a user supplied layout where near_copies or far_copies is zero, allowing a divide by zero when the improved far set layout computes disk geometry. A local actor who can configure or assemble MD RAID10 arrays with a crafted layout can trigger a kernel fault and cause denial of service. For the CVSS the PR:H is used because reliable triggering normally requires administrative storage management privileges such as root or CAP_SYS_ADMIN through mdadm, sysfs, or ioctl interfaces. The issue is not network reachable and does not show evidence of memory corruption, information disclosure, or privilege escalation. Impact is availability only through a local privileged kernel crash or failed array setup.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DISK UAF LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=1

## 1. ActionableScore

* Conservative score: **1**
* Paranoid score: **1**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* **Reliable kernel crash / strong DoS: +1**
  A crafted RAID10 layout with `far_copies == 0` can trigger a divide-by-zero in `setup_geo()`.

* **Important filesystem/storage path: +1**
  The bug is in MD RAID10 geometry setup, which is a storage configuration path.

* **Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2**
  Reliable triggering normally requires control over MD RAID configuration via `mdadm`, sysfs, ioctl, or array assembly, which is generally restricted to root or equivalent storage-management privileges.

* **Availability impact realistic: +1**
  If triggered, the divide-by-zero can cause a local kernel fault or panic during array setup.

No memory corruption, UAF, OOB write, information disclosure, privilege escalation, or remote/network trigger is supported by the patch.

## 3. Reachability analysis

The issue is reachable by a local actor who can configure or assemble an MD RAID10 array with a crafted layout value. In normal deployments this requires administrative storage privileges. Namespaces or containers generally do not lower this requirement unless a container is given unusually broad block-device and MD management access. The path is not default-triggered by ordinary users and is not network reachable. A possible operational edge case is automatic assembly of untrusted external RAID metadata, but that is environment-specific and still does not imply memory corruption or LPE.

## 4. Severity interpretation

This behaves like a privileged local DoS in a storage configuration path, not an Important-class kernel vulnerability. The realistic impact is availability loss from a divide-by-zero during RAID10 setup. There is no evidence of a corruption primitive, privilege escalation path, or confidentiality/integrity impact.

## 5. One-sentence report phrase

A crafted MD RAID10 layout with zero `near_copies` or `far_copies` can trigger a divide-by-zero in `setup_geo()`, causing a privileged local denial of service during array setup.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

The bug is a straightforward input-validation issue causing privileged local DoS only, with no memory corruption, remote exposure, or privilege escalation evidence.

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

Patch: md/raid10: fix divide-by-zero in setup_geo() with zero far_copies
Commit: 4af2e558e6fdfb972c61350653fd55d1f62b60a5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4af2e558e6fdfb972c61350653fd55d1f62b60a5

Commit description:

setup_geo() extracts near_copies (nc) and far_copies (fc) from the
user-provided layout parameter without checking for zero. When fc=0
with the "improved" far set layout selected, 'geo->far_set_size =
disks / fc' triggers a divide-by-zero.

Validate nc and fc immediately after extraction, returning -1 if
either is zero.

Fixes: 475901a ("MD RAID10: Improve redundancy for 'far' and 'offset' algorithms (part 1)")
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://lore.kernel.org/linux-raid/SYBPR01MB7881A5E2556806CC1D318582AF232@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/raid10.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=4af2e558e6fdfb972c61350653fd55d1f62b60a5

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

The original Linux kernel CVE announcement for CVE-2026-46161 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46161

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  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: 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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).