[CVE-2026-80555][MODERATE REGULAR] s390/vfio_ccw: Free all memory if cp_init() fails

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

CVE: CVE-2026-80555
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/vfio_ccw: Free all memory if cp_init() fails
Commit: 6a917199aaf97904f5619afe3dfdacb155b03e8c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6a917199aaf97904f5619afe3dfdacb155b03e8c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80555
Analysis date: Wed, 26 Aug 2026 11:38:55 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like for generic environments. Borderline only when s390 vfio_ccw passthrough is in production scope
Manual review required: NO

Summary:
`s390 vfio_ccw may leak ccwchain memory when cp_init() fails after TIC based channel program expansion, allowing a guest or local vfio_ccw user to cause host memory exhaustion DoS in affected s390 passthrough deployments.`

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

The original Linux kernel CVE announcement for CVE-2026-80555 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80555

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80555	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:L';BEST CVSS score: '5.6';DESCR 's390/vfio_ccw can leak ccwchain allocations when cp_init() fails after building multiple channel program segments through Transfer in Channel processing. A guest or local process with access to an assigned vfio_ccw device may be able to repeat failing I/O setup and gradually consume host kernel memory, causing denial of service. For the CVSS the PR:L is used for the paranoid score because triggering requires control of a guest or a process that can submit I/O through an already assigned vfio_ccw device, but does not require full host administrator privileges. The issue is not network reachable and is limited to s390 systems using vfio_ccw passthrough. Impact is resource exhaustion and host availability loss. No concrete memory corruption primitive is indicated, so confidentiality and integrity are not raised.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like for generic environments. Borderline only when s390 vfio_ccw passthrough is in production scope (with actual score 3)	YES	OOB INIT SIMPLEFIX LEAK LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like for generic environments. Borderline only when s390 vfio_ccw passthrough is in production scope**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A guest or local process with access to an already assigned vfio_ccw device may be able to submit channel programs that reach `cp_init()` failure paths.

* Reliable kernel crash / strong DoS: +1
  The issue is a memory leak of allocated `ccwchain` segments. Repeated failures may gradually exhaust host kernel memory.

* Cross-boundary isolation/resource concern: +1 in paranoid score only
  If triggered from a guest, the leak consumes host kernel memory, so it can behave as a guest-to-host resource exhaustion issue.

Subtract signals:

* Rare AND difficult-to-reach subsystem/configuration: -1
  This is limited to s390 systems using `vfio_ccw` passthrough and channel programs involving TIC-created chains.

Not triggered:

* Generic memory corruption: +0
  The patch shows a memory leak cleanup bug, not UAF, double-free, OOB write, refcount takeover, or type confusion.

* Privilege escalation plausible: +0
  No concrete LPE primitive is indicated.

* Confidentiality impact plausible: +0
  No leak of sensitive data or read primitive is shown.

* Integrity impact plausible: +0
  No write primitive or cross-object corruption is shown.

## 3. Reachability analysis

The bug can be triggered only where s390 `vfio_ccw` is used and a guest or process can issue I/O through an assigned channel device. It is not network reachable. It is not a default broad Linux attack surface. Host administrator action is normally required to configure passthrough, but once the device is assigned, the triggering actor may be a guest-controlled workload rather than full host root. Containers and namespaces do not materially broaden reachability unless they are also given access to the relevant vfio device.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak for most environments. It becomes a borderline actionable Moderate only for deployments that actually use s390 `vfio_ccw` passthrough with untrusted guests. The theoretical impact is host memory exhaustion, but the patch does not support memory corruption, privilege escalation, confidentiality impact, or integrity impact.

## 5. One-sentence report phrase

`s390 vfio_ccw may leak ccwchain memory when cp_init() fails after TIC based channel program expansion, allowing a guest or local vfio_ccw user to cause host memory exhaustion DoS in affected s390 passthrough deployments.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

For generic product triage this can be auto-closed or deprioritized unless s390 `vfio_ccw` passthrough is in supported production scope. If that environment is in scope, a targeted manual check is reasonable, but the bug class remains resource exhaustion without demonstrated memory corruption.

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

Patch: s390/vfio_ccw: Free all memory if cp_init() fails
Commit: 6a917199aaf97904f5619afe3dfdacb155b03e8c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6a917199aaf97904f5619afe3dfdacb155b03e8c

Commit description:

The routine cp_free() is called to unpin/free any memory once an I/O
is completed successfully, or if cp_prefetch() fails. But if cp_init()
fails, and cp->initialized is not enabled, the same routine cannot be
used to free all the memory.

An attempt to address this exists in ccwchain_handle_ccw(), where a
single call to ccwchain_free() is made for the currently-processed
CCW segment. But this will leak other segments (created as a result
of a Transfer in Channel) that had been allocated as part of the same
channel program.

Address this by performing the cleanup outside of the recursive
ccwchain_handle_ccw()/ccwchain_loop_tic() logic.

Fixes: 8b515be ("vfio-ccw: Fix memory leak and don't call cp_free in cp_init")
Cc: stable@vger.kernel.org
Reviewed-by: Farhan Ali <alifm@linux.ibm.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_cp.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=6a917199aaf97904f5619afe3dfdacb155b03e8c

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

The original Linux kernel CVE announcement for CVE-2026-80555 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80555

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:H/PR:L/UI:N/S:C/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.6

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).