[CVE-2026-46182][MODERATE REGULAR] pseries/papr-hvpipe: Prevent kernel stack memory leak to userspace

[CVE-2026-46182][MODERATE REGULAR] pseries/papr-hvpipe: Prevent kernel stack memory leak to userspace

[AL-KERNEL]

CVE: CVE-2026-46182
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: pseries/papr-hvpipe: Prevent kernel stack memory leak to userspace
Commit: 0479b6e9f999cc1cbad7d9f09f574fc387e605d5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0479b6e9f999cc1cbad7d9f09f574fc387e605d5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46182
Analysis date: Thu, 28 May 2026 10:33:26 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
`papr_hvpipe_handle_read()` could copy uninitialized padding bytes from a stack allocated `papr_hvpipe_hdr` to userspace, causing a local kernel stack information disclosure.

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

The original Linux kernel CVE announcement for CVE-2026-46182 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46182

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-2026-46182	MODERATE	CHECK	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:N/A:N';*CWE-457;*CWE-200;CWE-908;CWE-665;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'papr hvpipe read path copied a stack allocated papr_hvpipe_hdr to userspace after only initializing version and flags. Reserved padding bytes could contain uninitialized kernel stack data and be exposed to a local reader of the hvpipe interface. For the CVSS the PR:L is used for the paranoid score because a reduced privilege user or service with read access to the device can trigger the leak without full host administrative privileges. The issue is not network reachable. Impact is information disclosure only, with no supported memory corruption, arbitrary write, or direct privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) 	MAYBE	SIMPLEFIX LEAK HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user or service with read access to the PAPR hvpipe interface can trigger the copy to userspace.
* Confidentiality impact plausible: +1. Reserved padding bytes in a stack allocated header can expose uninitialized kernel stack data.

Paranoid additional signal:

* Repeated stack info leak concern: +1. If the interface is repeatedly readable by a reduced privilege user, leaked stack bytes may include useful kernel pointers or sensitive transient data.

Limiting factors:

* No memory corruption.
* No write primitive.
* No UAF, double free, OOB write, or arbitrary write.
* No network reachability.
* Platform specific to powerpc pseries PAPR hvpipe.

## 3. Reachability analysis

The issue is local and depends on access to the PAPR hvpipe read interface. It is not remotely network reachable.

Namespaces and containers matter only if this platform-specific interface is delegated into a container or exposed to reduced privilege services. In normal deployments, access control around the device or file interface determines whether this is a practical unprivileged leak.

## 4. Severity interpretation

This behaves like a borderline Moderate information disclosure issue. The realistic impact is leakage of a small, fixed amount of uninitialized kernel stack data through `copy_to_user()`.

It does not behave like an Important memory corruption issue. There is no evidence of privilege escalation, arbitrary write, or kernel object lifetime corruption.

## 5. One-sentence report phrase

`papr_hvpipe_handle_read()` could copy uninitialized padding bytes from a stack allocated `papr_hvpipe_hdr` to userspace, causing a local kernel stack information disclosure.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review is recommended to confirm permissions on the hvpipe interface and whether untrusted users can repeatedly read it. If access is strictly privileged, this can likely be treated as low-priority information disclosure.

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

Patch: pseries/papr-hvpipe: Prevent kernel stack memory leak to userspace
Commit: 0479b6e9f999cc1cbad7d9f09f574fc387e605d5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0479b6e9f999cc1cbad7d9f09f574fc387e605d5

Commit description:

The hdr variable is allocated on the stack and only hdr.version and
hdr.flags are initialized explicitly. Because the struct papr_hvpipe_hdr
contains reserved padding bytes (reserved[3] and reserved2[40]), these
could leak the uninitialized bytes to userspace after copy_to_user().

This patch fixes that by initializing the whole struct to 0.

Cc: stable@vger.kernel.org
Fixes: cebdb52 ("powerpc/pseries: Receive payload with ibm,receive-hvpipe-msg RTAS")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/7bfe03b65a282c856ed8182d1871bb973c0b78f2.1777606826.git.ritesh.list@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/powerpc/platforms/pseries/papr-hvpipe.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=0479b6e9f999cc1cbad7d9f09f574fc387e605d5

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

The original Linux kernel CVE announcement for CVE-2026-46182 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46182

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:L/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:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 2
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).