[CVE-2026-72290][LOW] KVM: s390: pci: Fix GISC refcount leak on AIF enable failure

[CVE-2026-72290][LOW] KVM: s390: pci: Fix GISC refcount leak on AIF enable failure

[AL-KERNEL]

CVE: CVE-2026-72290
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: KVM: s390: pci: Fix GISC refcount leak on AIF enable failure
Commit: 3882224b0e714f34de91e5f28307c5d3fccfe8f8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3882224b0e714f34de91e5f28307c5d3fccfe8f8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72290
Analysis date: Sat, 15 Aug 2026 03:27:09 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72290 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72290

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-2026-72290	LOW	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:H/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'KVM s390 PCI AIF enable can leak a GISC reference when kvm_s390_gisc_register() succeeds but a later setup step fails before interrupt forwarding is fully enabled. Repeated failed enable attempts may leave stale GISC references and can degrade or exhaust resources related to guest interrupt forwarding. For the CVSS the PR:H is selected because reliable triggering normally requires host side control of KVM VM setup and s390 PCI passthrough configuration. The issue is not network reachable and is triggered through local virtualization control paths. Impact is denial of service through resource leakage, with no concrete UAF, OOB access, information disclosure, or privilege escalation primitive visible from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	VIRT INIT SIMPLEFIX LEAK HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Real lifetime/refcount bug: +1. `kvm_s390_gisc_register()` succeeds, but the error unwind path missed `kvm_s390_gisc_unregister()`, leaving a leaked GISC reference.
* Availability impact realistic in paranoid interpretation: +1. Repeated failed AIF enable attempts could accumulate leaked references and degrade or exhaust interrupt-forwarding resources.
* Requires admin/root/CAP-level control: -2. Reliable triggering normally requires host-side KVM VM management and s390 PCI interrupt forwarding or passthrough configuration.
* Rare and difficult-to-reach subsystem/configuration: -1. This is limited to KVM on s390 with PCI AIF paths, not a broad default kernel interface.
* No remote reachability, no local unprivileged trigger, no UAF, no OOB access, no arbitrary write, no demonstrated LPE primitive.

3. Reachability analysis
The bug is reachable through local host virtualization control paths, not through guest packet/data input or the network. A normal unprivileged local user should not be able to trigger it unless they are delegated unusually broad KVM and PCI device-management access. Containers or namespaces do not normally lower this to PR:L unless the environment intentionally exposes host KVM device-management capabilities.

Call-site confidence: medium. The commit message clearly describes the failed unwind path and missing unregister, but the full caller context is not included in the provided diff.

4. Severity interpretation
This behaves like a low-end resource lifetime leak rather than an Important-class kernel vulnerability. The theoretical impact is DoS through resource exhaustion after repeated failures. There is no evidence of memory corruption, privilege escalation, information disclosure, guest-to-host escape, or attacker-controlled object reuse.

5. One-sentence report phrase
A missing `kvm_s390_gisc_unregister()` in the KVM s390 PCI AIF enable error path can leak GISC references after setup failures, potentially causing resource-exhaustion DoS in privileged host-side virtualization configurations.

6. Manual review recommendation
NO MANUAL CHECK NEEDED.
This is a privileged, rare-configuration refcount leak with no concrete memory corruption or security-boundary bypass primitive, so it can be handled as low-priority/autoclose unless product-specific s390 KVM PCI exposure is unusually broad.

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

Patch: KVM: s390: pci: Fix GISC refcount leak on AIF enable failure
Commit: 3882224b0e714f34de91e5f28307c5d3fccfe8f8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3882224b0e714f34de91e5f28307c5d3fccfe8f8

Commit description:

kvm_s390_gisc_register() registers the guest ISC before pinning
the guest interrupt forwarding pages and allocating the AISB bit.
If any of the later setup steps fails, the function unwinds the
pinned pages and other local state, but does not unregister the
GISC reference. Add the missing kvm_s390_gisc_unregister() to the
error unwind path.

Fixes: 3c5a1b6 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
Cc: stable@vger.kernel.org
Signed-off-by: Haoxiang Li <haoxiang_li2024@163.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260624061910.2794734-1-haoxiang_li2024@163.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/s390/kvm/pci.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=3882224b0e714f34de91e5f28307c5d3fccfe8f8

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

The original Linux kernel CVE announcement for CVE-2026-72290 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72290

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:N/I:N/A:L
  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: 0
  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).