[CVE-2026-72282][MODERATE 7.0] KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers

[CVE-2026-72282][MODERATE 7.0] KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers

[AL-KERNEL]

CVE: CVE-2026-72282
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers
Commit: f398b7d92cd999191249830b9171c9bd787a9a91
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f398b7d92cd999191249830b9171c9bd787a9a91
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72282
Analysis date: Sat, 15 Aug 2026 21:19:47 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A KVM SRCU lifetime race allowed `kvm_io_bus_get_dev()` to return an MMIO device pointer after dropping protection, so the arm64 VGIC ITS path could inspect a stale object and potentially trigger a host kernel crash or UAF-like memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-72282 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72282

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
======================================================================

CVE-2026-72282	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:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A lifetime race exists in the KVM MMIO bus lookup path because kvm_io_bus_get_dev returned a device pointer after dropping the SRCU read lock. The arm64 VGIC ITS doorbell lookup can then inspect a stale object if the matched MMIO device is removed or replaced concurrently. This is a UAF candidate in host kernel KVM code rather than a simple warning or resource leak. For the CVSS the PR:L is used because a local process with access to KVM VM control interfaces can race device lookup and device lifetime operations. The issue is not directly network reachable. Impact is at least local denial of service via host kernel crash and in the paranoid case may include confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB LOCK VIRT SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process with access to KVM VM control interfaces can potentially exercise the affected VGIC ITS MMIO device lookup path. This is PR:L rather than PR:H in practical KVM deployments where VM control is delegated to a QEMU or VM owner process.

* Memory corruption, weak or indirect corruption candidate: +1
  The helper returned a `kvm_io_device` pointer after dropping SRCU protection. The caller could later inspect a stale object. The patch supports a UAF candidate, but does not show attacker-controlled reclaim, overwrite, callback control, or arbitrary write.

* Real lifetime corruption: +1
  This is a real object lifetime issue caused by returning a pointer whose SRCU-protected lifetime no longer extends through caller introspection.

* Reliable kernel crash / strong DoS: +1
  A stale KVM MMIO device pointer in host kernel KVM code can plausibly lead to an Oops or host kernel crash.

* Broad or important virtualization subsystem exposure: +1
  KVM is an important host isolation subsystem. The affected path is arm64 VGIC ITS specific, but still security-relevant on arm64 virtualization hosts.

Negative signals:

* Hard or unreliable race / special timing required: -1
  Triggering requires racing KVM IO bus device lifetime changes with the VGIC ITS doorbell lookup.

Paranoid adjustment:

* Weak LPE concern: +1, capped by race-UAF downgrade guidance
  A stale pointer in host KVM code can in worst case become more than DoS if object reuse is reachable, but the patch does not demonstrate controlled reclaim or a write primitive. Therefore the paranoid score is capped at 5, not escalated to Important solely from the UAF class.

## 3. Reachability analysis

The bug is local to the host KVM interface and is not directly network reachable. The plausible attacker is a local VM-owning process or a process with access to `/dev/kvm` and relevant VM device operations. In many deployments this is not full host root, because QEMU or a VM management service may run with reduced privileges, so PR:L is more appropriate than PR:H for practical triage. Namespaces and containers may matter if KVM access is delegated into a container, but ordinary unprivileged users without KVM access cannot trigger it. The path is specific to arm64 KVM VGIC ITS MMIO device lookup, so exposure depends on arm64 virtualization with ITS support.

Call-site confidence: high. The patch shows the only caller being changed to hold SRCU across `kvm_io_bus_get_dev()` and subsequent object use.

## 4. Severity interpretation

This behaves like an actionable Moderate issue, with Important-class review sensitivity because it is a KVM host-kernel lifetime race. The realistic demonstrated impact is local host DoS through stale pointer use or UAF-like behavior. The theoretical memory corruption potential is higher because KVM object lifetime bugs can sometimes become host memory corruption or LPE, but this patch does not show controlled reclaim, attacker-controlled overwrite, callback dispatch, or arbitrary read/write. Therefore the conservative score stays borderline at 4, while the paranoid actionable score is 5.

## 5. One-sentence report phrase

A KVM SRCU lifetime race allowed `kvm_io_bus_get_dev()` to return an MMIO device pointer after dropping protection, so the arm64 VGIC ITS path could inspect a stale object and potentially trigger a host kernel crash or UAF-like memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a host KVM lifetime race with a plausible stale pointer or UAF primitive. Even though exploitation beyond DoS is not demonstrated, KVM host isolation bugs should not be auto-closed without manual review.

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

Patch: KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers
Commit: f398b7d92cd999191249830b9171c9bd787a9a91
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f398b7d92cd999191249830b9171c9bd787a9a91

Commit description:

kvm_io_bus_get_dev() returns a device that is only matched by the
address, and nothing else. This can cause a lifetime issue if
the matched device is not the expected type, as by the time
the caller can introspect the object, it might be gone (the srcu
lock having been dropped).

Given that there is only a single user of this helper, the simplest
option is to move the locking responsibility to the caller, which
can keep the srcu lock held for as long as it wants.

Note that this aligns with other kvm_io_bus*() helpers, which
already require the srcu lock to be held by the callers.

Reported-by: Will Deacon <will@kernel.org>
Fixes: 8a39d00 ("KVM: kvm_io_bus: Add kvm_io_bus_get_dev() call")
Link: https://lore.kernel.org/all/20260626111344.802555-1-maz@kernel.org
Cc: stable@vger.kernel.org
Reviewed-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20260627105105.1005990-1-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kvm/vgic/vgic-its.c
  virt/kvm/kvm_main.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=f398b7d92cd999191249830b9171c9bd787a9a91

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

The original Linux kernel CVE announcement for CVE-2026-72282 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72282

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: 4
  Paranoid ActionableScore: 5

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 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).