[CVE-2026-43097][LOW] PCI: hv: Fix double ida_free in hv_pci_probe error path [ Upstream

[CVE-2026-43097][LOW] PCI: hv: Fix double ida_free in hv_pci_probe error path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-43097
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: PCI: hv: Fix double ida_free in hv_pci_probe error path [ Upstream
Commit: 21bc8e0ba5c2a081b0a2808c976d4c9dbddf1e48
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21bc8e0ba5c2a081b0a2808c976d4c9dbddf1e48
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43097
Analysis date: Mon, 27 Jul 2026 22:15:10 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A Hyper-V PCI probe error path can release the same emulated PCI domain ID twice, causing an IDA warning and possible DoS only on panic_on_warn systems, with no demonstrated memory corruption or privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-43097 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43097

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-2026-43097	LOW	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:H/UI:N/S:U/C:N/I:N/A:H';*CWE-672;CWE-763;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'A double release of an emulated PCI domain ID can occur in the Hyper-V PCI probe error path because the driver explicitly frees bridge domain_nr and PCI core later frees the same ID during host bridge release. This is an ID allocator double free warning rather than a clear memory double free, and the patch context does not show a UAF, OOB access, or arbitrary write primitive. For the CVSS the PR:H is used because reliable triggering typically requires administrative control over Hyper-V PCI probing, device hotplug, module handling, or an induced probe failure in the guest. The issue is not network reachable and the realistic impact is limited to availability, mainly a warning or a kernel panic when panic_on_warn is enabled.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	WARNONLY ERRORPATH HARDWARE 	-	-	guess

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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

Conservative signals:

* Requires admin/root/host-level control in typical deployments: -2. Reliable triggering requires Hyper-V PCI probe manipulation, device hotplug, module/probe failure control, or host-side conditions.
* Rare/configuration-dependent path: -1. The bug is specific to the Hyper-V PCI controller probe error path.
* No strong memory corruption signal: +0. This is an ID allocator double release warning, not a demonstrated heap double-free, UAF, OOB write, stale callback, or arbitrary write.
* WARN only: +0. The commit shows `ida_free called for id which is not allocated` and a WARN trace, but not a normal panic or exploitable corruption path.

Paranoid additional signal:

* Availability concern under `panic_on_warn`: +1. If the target enables `panic_on_warn`, the WARN can become a kernel panic and local/host-triggered DoS.

Call-site confidence: high. The patch shows both the bad explicit `pci_bus_release_emul_domain_nr()` path and the PCI core release callback path.

## 3. Reachability analysis

The bug is reachable only when `hv_pci_probe()` fails after `hbus->bridge->domain_nr` has been stored and before normal initialization completes. In typical deployments, a guest-local unprivileged user cannot reliably force this exact probe error path. Practical triggering generally requires administrative guest control, Hyper-V device hotplug/probe control, or host/hypervisor influence.

Namespaces and containers do not materially lower privileges because this is not a normal namespaced syscall, netlink, or unprivileged device API path. The affected code is not network reachable. The subsystem is relevant mainly for Hyper-V guests with PCI pass-through or synthetic PCI support.

## 4. Severity interpretation

This behaves like a Low or ordinary Moderate reliability issue, not an Important-class vulnerability. The theoretical concern is a double release of an IDA-managed identifier, but the patch context does not show memory object reuse, UAF, OOB access, arbitrary write, type confusion, or privilege escalation potential. Realistic impact is a warning, or DoS only on systems where warnings are fatal.

## 5. One-sentence report phrase

A Hyper-V PCI probe error path can release the same emulated PCI domain ID twice, causing an IDA warning and possible DoS only on panic_on_warn systems, with no demonstrated memory corruption or privilege escalation primitive.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: no network exposure, no unprivileged trigger in typical deployments, no concrete memory corruption primitive, and realistic impact is limited to warning or configuration-dependent panic.

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

Patch: PCI: hv: Fix double ida_free in hv_pci_probe error path [ Upstream
Commit: 21bc8e0ba5c2a081b0a2808c976d4c9dbddf1e48
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21bc8e0ba5c2a081b0a2808c976d4c9dbddf1e48

Changed files:
  lib/idr.c
  drivers/pci/controller/pci-hyperv.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=21bc8e0ba5c2a081b0a2808c976d4c9dbddf1e48

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

The original Linux kernel CVE announcement for CVE-2026-43097 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43097

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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).