[CVE-2026-72283][MODERATE 7.0] KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails

[CVE-2026-72283][MODERATE 7.0] KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails

[AL-KERNEL]

CVE: CVE-2026-72283
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails
Commit: d1379888cc4230bac647ec24ab83306afbd03e88
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1379888cc4230bac647ec24ab83306afbd03e88
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72283
Analysis date: Sat, 15 Aug 2026 09:11:10 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A dangling `irqfd->producer` pointer in the KVM x86 IRQ bypass path can survive a failed IRTE update and later reference a separately freed VFIO producer object, creating a host-kernel use-after-free reachable by a local VM or device-management context.

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

The original Linux kernel CVE announcement for CVE-2026-72283 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72283

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 7.0
Manual review required: YES

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-2026-72283	MODERATE	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:H/I:H/A:H';*CWE-416;CWE-825;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A dangling pointer use-after-free can occur in the KVM x86 irqfd bypass path when kvm_pi_update_irte() fails while updating an IRTE for MSI bypass. The irqfd producer pointer can remain set even though the producer object may later be freed independently, for example when a VFIO PCI interrupt vector is disabled. If the irqfd remains reachable through KVM routing, later KVM operations may dereference stale host kernel memory. For the CVSS the PR:L because a local host process with access to KVM irqfd and VFIO device assignment or equivalent VM management control is needed for reliable triggering. The issue is not directly network reachable. Impact is at least local denial of service via host kernel crash and in worst case may allow confidentiality or integrity impact due to the use-after-free condition.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-72283 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 77e1b8332d1d7aa786f7515e9bd4055def6a1e06 YES  NO NO unknown 	MAYBE	DANGER VIRT UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local reduced-privilege trigger: +1**. Triggering appears local through KVM irqfd and VFIO or equivalent VM device-assignment control, not remote network traffic.
* **Generic memory corruption, strong primitive: +2**. The commit explicitly describes a dangling pointer that can result in use-after-free.
* **Real lifetime corruption: +1**. `irqfd->producer` can outlive the separately freed producer object.
* **Reliable kernel crash / strong DoS: +1**. A stale producer pointer reachable through KVM routing can plausibly crash the host kernel.
* **Privileged kernel/device-management memory corruption path: +1**. The bug is in KVM IRQ bypass / VFIO PCI interrupt handling, a trusted host kernel virtualization path.
* **Hard or special conditions required: -1**. The issue depends on failed IRTE bypass update plus producer lifetime changes such as VFIO vector disable while routing remains reachable.

Paranoid additions:

* **Weak LPE concern: +1**. The stale pointer is in host kernel KVM/VFIO state, so privilege escalation cannot be dismissed even though no reclaim or controlled overwrite primitive is shown.
* **Integrity impact plausible: +1**. In paranoid triage, host-kernel UAF in a virtualization/device-management path justifies manual review for possible integrity impact.

Not counted:

* **Remote reachable: +0**. No direct network path is shown.
* **Strong LPE plausibility: +0**. No attacker-controlled reclaim, arbitrary write, callback control, or object replacement is demonstrated.
* **Confidentiality impact in conservative score: +0**. No leak or read primitive is shown.

## 3. Reachability analysis

The likely trigger is a local host process that can create or manage KVM irqfd routing together with VFIO PCI interrupt assignment. This is commonly available to VM management stacks or users granted access to `/dev/kvm` and VFIO device nodes, but not to arbitrary remote attackers. Namespaces and containers may matter if a reduced-capability service account, container root, or delegated VM-management user can operate assigned VFIO devices without full host-root equivalence. The affected path is not default for all systems, but it is relevant on virtualization hosts using KVM with VFIO PCI passthrough and IRQ bypass.

Call-site confidence: **medium**. The patch context and commit message directly identify the dangling `irqfd->producer` lifetime issue, but the full later dereference path is not included in the pasted diff.

## 4. Severity interpretation

This is not an ordinary DoS-only validation bug. The commit explicitly identifies a dangling pointer and use-after-free in a host kernel KVM path. Realistic exploitation evidence is limited because the trigger requires specific KVM/VFIO state and an IRTE update failure, and no controlled reclaim or write primitive is shown. Conservatively it is an **Actionable Moderate** host-kernel UAF with reliable DoS potential. Paranoid triage makes it a **Strong Important candidate** because KVM/VFIO lifetime bugs can cross a strong virtualization boundary and deserve manual review.

## 5. One-sentence report phrase

A dangling `irqfd->producer` pointer in the KVM x86 IRQ bypass path can survive a failed IRTE update and later reference a separately freed VFIO producer object, creating a host-kernel use-after-free reachable by a local VM or device-management context.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

This is an explicit KVM/VFIO use-after-free candidate in host kernel memory. Even though the practical trigger is conditional and no controlled exploitation primitive is shown, it should not be auto-closed because virtualization lifetime bugs can have impact beyond a simple crash.

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

Patch: KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails
Commit: d1379888cc4230bac647ec24ab83306afbd03e88
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1379888cc4230bac647ec24ab83306afbd03e88

Commit description:

Nullify irqfd->producer if updating the IRTE for bypass fails, as leaving a
dangling pointer will result in a use-after-free if the irqfd is reachable
through KVM's routing, but the producer is freed separately.  E.g. for VFIO
PCI, the producer is embedded in struct "vfio_pci_irq_ctx" and freed when
the vector is disabled, which can happen independent of routing updates.

Fixes: 77e1b83 ("KVM: x86: Decouple device assignment from IRQ bypass")
Cc: stable@vger.kernel.org
Signed-off-by: leixiang <leixiang@kylinos.cn>
Link: https://patch.msgid.link/1782119051448443.14545.seg@mailgw.kylinos.cn
[sean: drop PPC change, massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kvm/irq.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=d1379888cc4230bac647ec24ab83306afbd03e88

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

The original Linux kernel CVE announcement for CVE-2026-72283 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72283

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 5
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).