[CVE-2026-64474][LOW] vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc

[CVE-2026-64474][LOW] vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc

[AL-KERNEL]

CVE: CVE-2026-64474
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc
Commit: 8e872c07e40d51a66dee7b280a23a460a2e1e3fa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e872c07e40d51a66dee7b280a23a460a2e1e3fa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474
Analysis date: Sat, 25 Jul 2026 08:09:06 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local process with VFIO migration control access can trigger an infinite loop in vfio_mig_get_next_state on blocked PRE_COPY transitions, causing a soft lockup or kernel panic, but the issue is not network reachable and does not show memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64474 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474

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-2026-64474	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'vfio_mig_get_next_state can enter an infinite loop when a blocked migration transition resolves to VFIO_DEVICE_STATE_ERROR and the skip loop keeps following the ERROR sentinel back to itself. A local process with access to the VFIO device migration control path can trigger this through transitions such as STOP_COPY to PRE_COPY or STOP_COPY to PRE_COPY_P2P on a precopy capable device. For the CVSS the PR:L is used because the attacker needs local access to a VFIO device or a VM manager context with migration control, but full host root is not necessarily required when VFIO access is delegated. The issue is not network reachable and does not provide a memory corruption primitive. Impact is denial of service through a soft lockup or kernel panic when softlockup_panic is enabled.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	DEADLOCK DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local delegated trigger: +1
  A local process with access to VFIO migration controls can request the problematic state transition. This is not generally remote and not broadly unprivileged, but VFIO access may be delegated to a VM manager or non-root service account.

* Reliable kernel crash / strong DoS: +1
  The blocked transition can cause an infinite loop while holding the driver state mutex, leading to soft lockup and possibly panic when softlockup_panic is enabled.

Not triggered:

* Remote reachable: +0
  No network packet or remote protocol path is involved.

* Memory corruption: +0
  The patch fixes an infinite loop on the VFIO_DEVICE_STATE_ERROR sentinel. There is no UAF, OOB access, double free, refcount misuse, stale pointer reuse, or arbitrary write primitive.

* Privilege escalation plausible: +0
  No LPE primitive is indicated. The issue is DoS-only.

* Confidentiality / Integrity: +0
  No information disclosure or data modification path is shown.

* Rare configuration penalty: 0
  VFIO migration and precopy-capable devices are not universal, but this is still a normal VFIO control path for affected deployments, so I would not strongly penalize it.

## 3. Reachability analysis

The bug can be triggered by a local actor that can operate the VFIO device migration state machine, typically a VM manager such as QEMU or a process with delegated VFIO device access. Full host root is not always required in practical deployments, but generic unprivileged local users usually do not have this access by default.

Namespaces and containers may matter if VFIO device access is delegated into a container or service context, but this does not become a normal unprivileged namespace attack. The path is not network reachable. Realistic exploitation requires an affected VFIO migration-capable device and a transition such as STOP_COPY to PRE_COPY or STOP_COPY to PRE_COPY_P2P on a precopy-capable setup.

## 4. Severity interpretation

This behaves like an ordinary Moderate / Low-like kernel DoS issue, not an Important-class vulnerability. The realistic impact is a local denial of service through soft lockup or panic in configurations where VFIO migration is available and softlockup_panic may convert the lockup into a crash.

There is no demonstrated memory corruption, no security boundary bypass, no sensitive-object access, and no privilege escalation primitive. Theoretical severity should not be raised solely because the affected code is in VFIO or because the loop runs in kernel context.

## 5. One-sentence report phrase

A local process with VFIO migration control access can trigger an infinite loop in vfio_mig_get_next_state on blocked PRE_COPY transitions, causing a soft lockup or kernel panic, but the issue is not network reachable and does not show memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as a DoS-only VFIO state-machine bug unless the evaluated product delegates VFIO migration controls to untrusted tenants or exposes a specific virtualization management path that makes triggering unusually easy.

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

Patch: vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc
Commit: 8e872c07e40d51a66dee7b280a23a460a2e1e3fa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e872c07e40d51a66dee7b280a23a460a2e1e3fa

Commit description:

vfio_mig_get_next_state() walks vfio_from_fsm_table[] one step at a time,
looping to skip optional states the device does not support until
*next_fsm is supported. A blocked transition is encoded as
VFIO_DEVICE_STATE_ERROR, which the trailing return reports as -EINVAL.

The skip loop does not account for the ERROR sentinel.
state_flags_table[ERROR] is ~0U and vfio_from_fsm_table[ERROR][*] is
ERROR, so once *next_fsm becomes ERROR the loop condition stays true and
*next_fsm never changes. The blocked arcs STOP_COPY -> PRE_COPY and
STOP_COPY -> PRE_COPY_P2P map to ERROR yet pass the support check on a
precopy-capable device, causing the loop to spin forever while holding
the driver state mutex. This can result in a soft lockup, and a panic
with softlockup_panic set.

Terminate the skip loop on the ERROR sentinel so a blocked transition
falls through to the existing return and reports -EINVAL.

Fixes: 4db5260 ("vfio: Extend the device migration protocol with PRE_COPY")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/SYBPR01MB7881290BBDE79B61AE6A017FAF122@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/vfio/vfio_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=8e872c07e40d51a66dee7b280a23a460a2e1e3fa

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

The original Linux kernel CVE announcement for CVE-2026-64474 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: unknown
  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).