[CVE-2026-64473][MODERATE 7.0] vfio: Remove device debugfs before releasing devres

[CVE-2026-64473][MODERATE 7.0] vfio: Remove device debugfs before releasing devres

[AL-KERNEL]

CVE: CVE-2026-64473
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vfio: Remove device debugfs before releasing devres
Commit: 6cc60b41d61657dc469893d14e8e55d160056ff1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cc60b41d61657dc469893d14e8e55d160056ff1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64473
Analysis date: Sat, 25 Jul 2026 10:26:18 -0400
ActionableScore: 7
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
VFIO debugfs entries could remain visible after devres-backed seqfile private data was released during device unregister, creating a local stale pointer UAF risk with likely DoS impact and possible higher impact if the freed object is reused.

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

The original Linux kernel CVE announcement for CVE-2026-64473 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64473

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-2026-64473	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-672;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7';DESCR 'VFIO per-device debugfs files created with debugfs_create_devm_seqfile can keep inode private data that is backed by devres. During device unregister the old order called device_del before removing the debugfs tree, so devres could be released while debugfs entries were still visible and readable. A local attacker with access to the affected VFIO debugfs files could race device unregister and trigger a stale private data dereference, which is a use-after-free risk. For the CVSS the PR:L is used in the paranoid score because a local process with delegated VFIO or debugfs access may be able to interact with the stale entries without full host administration. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to UAF memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	INIT SIMPLEFIX HARDWARE DEBUGFS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Real lifetime corruption: +1. `debugfs_create_devm_seqfile()` stores devres-backed inode private data, and `device_del()` can release devres while debugfs entries remain visible.
* Memory corruption, weak or indirect corruption candidate: +1. The stale inode private data is a credible UAF pattern, but the patch does not demonstrate attacker-controlled reclaim or overwrite.
* Reliable kernel crash / strong DoS: +1. Reading a debugfs seqfile backed by freed private data can plausibly crash the kernel.
* Hard or unreliable race / teardown timing required: -1. The issue requires interaction with device unregister while debugfs entries are still accessible.
* Requires admin/root/CAP privileges in typical deployments: -2. VFIO device unregister and debugfs access are usually administrator-controlled.

Paranoid additional signals:

* Local trigger with delegated access: +1. In some deployments, VFIO/debugfs access may be delegated to a service account, VM manager, container root, or reduced-capability root rather than full host root.
* Privilege escalation plausible: +2. `debugfs_create_devm_seqfile()` style objects commonly carry callback/read context through inode private data, so stale private data can become more serious than a plain NULL dereference if freed memory is reused.
* Generic memory corruption, strong UAF candidate: +2. The bug is a stale pointer after free in a debugfs seqfile path, not just a validation or bookkeeping issue.
* Real lifetime corruption: +1.
* Reliable kernel crash / strong DoS: +1.
* Privileged kernel/device-management lifetime path: +1. The corruption occurs in VFIO device teardown/devres lifetime management, a trusted device-management context.
* Hard teardown race: -1.

Call-site confidence: high. The unregister ordering is shown directly, and the commit explicitly identifies devres-backed inode private data surviving after `device_del()`.

## 3. Reachability analysis

The issue is local, not network reachable. A practical trigger requires access to the affected VFIO per-device debugfs files and a concurrent VFIO device unregister path. In normal host deployments this is usually root or an administrator-level service, so the conservative score is low. In virtualization environments, VFIO device management may be performed by reduced-privilege service accounts or delegated management components, so the paranoid interpretation treats this as PR:L rather than full PR:H.

The affected debugfs view is diagnostic and may not be mounted or exposed in hardened systems. However, if it is exposed, the stale private-data window is a real lifetime bug during teardown.

## 4. Severity interpretation

This is not an ordinary Moderate correctness fix. Conservatively, it behaves like a local privileged teardown UAF with likely DoS impact. Paranoid handling is justified because the stale object is used as debugfs seqfile private data, which can involve callback/context dereference after devres release. There is no evidence of remote reachability or a demonstrated exploit chain, but the lifetime/callback pattern is risky enough to avoid auto-closure.

## 5. One-sentence report phrase

VFIO debugfs entries could remain visible after devres-backed seqfile private data was released during device unregister, creating a local stale pointer UAF risk with likely DoS impact and possible higher impact if the freed object is reused.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real lifetime/UAF pattern in a VFIO debugfs seqfile teardown path, and the risk depends heavily on actual debugfs permissions, VFIO delegation model, and whether the stale private data can reach callback or controlled-object reuse.

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

Patch: vfio: Remove device debugfs before releasing devres
Commit: 6cc60b41d61657dc469893d14e8e55d160056ff1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cc60b41d61657dc469893d14e8e55d160056ff1

Commit description:

VFIO device debugfs files created with debugfs_create_devm_seqfile()
store a devres allocated debugfs_devm_entry as inode private data.
vfio_unregister_group_dev() currently calls vfio_device_del() before
vfio_device_debugfs_exit(), but device_del() releases devres.  This can
leave debugfs entries visible with stale inode private data while
unregister waits for userspace references to drain.

Remove the per-device debugfs tree before vfio_device_del().  The debugfs
view is diagnostic only, so losing it at the start of unregister is
preferable to preserving entries whose backing storage may already have
been released.

Complete the teardown by clearing the per-device debugfs root after
removal.  This matches the global debugfs root cleanup and prevents
future users from mistaking a removed dentry for a live debugfs tree
during the remainder of unregister.

Fixes: 2202844 ("vfio/migration: Add debugfs to live migration driver")
Reported-by: Sashiko AI Review <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/r/20260615192725.6A2221F000E9@smtp.kernel.org
Cc: stable@vger.kernel.org
Cc: Longfang Liu <liulongfang@huawei.com>
Assisted-by: OpenAI Codex:gpt-5
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20260615204717.735302-1-alex.williamson@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/vfio/debugfs.c
  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=6cc60b41d61657dc469893d14e8e55d160056ff1

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

The original Linux kernel CVE announcement for CVE-2026-64473 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64473

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:L/I:N/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: 3
  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).