[CVE-2026-64105][LOW] KVM: arm64: vgic: Free private_irqs when init fails after allocation

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

CVE: CVE-2026-64105
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: KVM: arm64: vgic: Free private_irqs when init fails after allocation
Commit: 173fb86e5519dbe7aabed1f5fa7456152a4a2e38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=173fb86e5519dbe7aabed1f5fa7456152a4a2e38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64105
Analysis date: Sun, 19 Jul 2026 17:23:54 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
KVM arm64 VGIC vCPU creation may leak private IRQ resources when initialization fails after allocation, allowing a local KVM-capable user to potentially cause resource exhaustion, but the patch does not indicate memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64105 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64105

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64105	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'KVM arm64 vCPU creation can leak vgic private_irqs when kvm_vgic_vcpu_init fails after allocating them but before the failed vCPU is released. A local attacker with access to KVM vCPU creation may be able to repeat this failure path and gradually consume kernel memory or related resources. For the CVSS the PR:L is used because triggering requires local access to KVM ioctls through /dev/kvm or an equivalent VMM process context, not full host administrator rights in common deployments. The issue is not network reachable and does not provide an apparent read write or UAF primitive. Impact is denial of service through resource exhaustion, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	VIRT SIMPLEFIX HARDWARE LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user or VMM process with access to `/dev/kvm` may be able to exercise vCPU creation paths. This is PR:L, not PR:H, in common KVM deployments where `/dev/kvm` is delegated to non-root users.
* Availability impact realistic: +1 in paranoid scoring only
  The leak could theoretically be accumulated by repeated failed vCPU creation attempts, causing memory or resource exhaustion over time.

Negative or non-triggered signals:

* Hard or unreliable failure condition: -1
  The leak requires `kvm_vgic_vcpu_init()` to fail after private IRQ allocation, specifically around redistributor iodev registration failure. This is an error path, not a normal reliable data path.
* Rare and configuration-specific path: -1 in conservative reasoning
  This affects KVM arm64 VGIC initialization and a narrow failed vCPU creation path.
* No generic memory corruption: +0
  The patch fixes missing cleanup, not UAF, double-free, OOB write, type confusion, or refcount takeover.
* No privilege escalation plausible: +0
  No attacker-controlled reclaim, stale object reuse, write primitive, callback control, or object confusion is shown.
* No confidentiality or integrity impact: +0
  The issue is a resource leak only.
* No remote reachability: +0
  The path is local KVM control-plane usage, not network-triggerable.

Call-site confidence: high. The patch shows the relevant error path in `kvm_arch_vcpu_create()` and the missing cleanup call.

## 3. Reachability analysis

The bug can be triggered only by a local actor able to create KVM vCPUs on arm64. In typical deployments this means a user in the KVM access group, a VMM process, or a container or service account that has been delegated `/dev/kvm`. It does not require full host root if KVM access is delegated, so PR:L is the practical interpretation.

Namespaces or containers matter only if `/dev/kvm` is exposed into them. Without KVM device access, an unprivileged container cannot reach this path. The affected code is not network reachable and is not in a packet-processing or guest-to-host data path. Realistic exploitation also depends on repeatedly hitting a specific VGIC initialization failure after `private_irqs` allocation, which makes the issue less actionable than ordinary local KVM memory corruption.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak, not an Important-class vulnerability. The realistic impact is local denial of service through gradual resource exhaustion if the failure path can be repeatedly triggered.

Theoretical worst case is host resource exhaustion from repeated failed vCPU creation. There is no evidence of memory corruption, UAF, stale pointer reuse, arbitrary write, page-cache corruption, or privilege escalation. Because the primitive is a cleanup omission in an initialization error path, manual exploitability risk is low.

## 5. One-sentence report phrase

KVM arm64 VGIC vCPU creation may leak private IRQ resources when initialization fails after allocation, allowing a local KVM-capable user to potentially cause resource exhaustion, but the patch does not indicate memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as a low-priority resource leak unless the affected product exposes `/dev/kvm` broadly and has evidence that the VGIC init failure path can be triggered reliably at scale.

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

Patch: KVM: arm64: vgic: Free private_irqs when init fails after allocation
Commit: 173fb86e5519dbe7aabed1f5fa7456152a4a2e38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=173fb86e5519dbe7aabed1f5fa7456152a4a2e38

Commit description:

Companion to commit 250f253 ("KVM: arm64: Tear down vGIC on
failed vCPU creation"), which added the missing kvm_vgic_vcpu_destroy()
call to the kvm_share_hyp() failure path in kvm_arch_vcpu_create(). The
kvm_vgic_vcpu_init() failure path immediately above it has the same
shape and still needs the same cleanup.

Call kvm_vgic_vcpu_destroy() when kvm_vgic_vcpu_init() fails so private
IRQs allocated before a redistributor iodev registration failure are
released before the failed vCPU is freed.

Fixes: 03b3d00 ("KVM: arm64: vgic: Allocate private interrupts on demand")
Cc: stable@vger.kernel.org
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://lore.kernel.org/r/20260519135042.2219239-1-michael.bommarito@gmail.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kvm/arm.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=173fb86e5519dbe7aabed1f5fa7456152a4a2e38

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

The original Linux kernel CVE announcement for CVE-2026-64105 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64105

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:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  Paranoid ActionableScore: 2

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).