[CVE-2026-74313][MODERATE 7.0] vduse: hold vduse_lock across IDR lookup in open path [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74313
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vduse: hold vduse_lock across IDR lookup in open path [ Upstream
Commit: 35483c5306e09b3190ff937089d404a78012695c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=35483c5306e09b3190ff937089d404a78012695c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74313
Analysis date: Sat, 15 Aug 2026 07:18:49 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local race in the VDUSE open path can allow `struct vduse_dev` to be freed by `VDUSE_DESTROY_DEV` after IDR lookup but before the open path takes `dev->lock`, causing a use-after-free with realistic kernel crash impact and weak privilege-escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-74313 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74313

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-2026-74313	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-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the VDUSE open path can lead to a use-after-free of struct vduse_dev. `vduse_dev_open()` looked up the device in the IDR and then dropped the global vduse_lock before taking the per device lock, leaving a window where VDUSE_DESTROY_DEV could remove and free the same object. A local attacker with access to the VDUSE device interface could race open against destroy and make the kernel operate on freed memory. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local code execution and access to the VDUSE interface, but this access may be delegated to a service account, container root, or reduced capability process rather than full host administrator rights. Impact is at least local denial of service via kernel crash. In the worst case this UAF may allow confidentiality or integrity impact 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	LOCK RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged or low-privileged trigger: +1
  Triggering requires local access to VDUSE device/control interfaces. This is not remote, but access may be delegated to a service account, container root, or reduced-capability process rather than full host root.

* Memory corruption, weak race-UAF primitive: +1
  The patch explicitly fixes a race where `vduse_dev_open()` can keep using `struct vduse_dev` after concurrent `VDUSE_DESTROY_DEV` removes and frees it.

* Real lifetime corruption: +1
  This is a real object lifetime bug involving IDR lookup, object removal, free, and later locking/use of the stale object pointer.

* Reliable kernel crash / strong DoS: +1
  A stale `dev` pointer can be passed to `mutex_lock()` and later used by the open path, making kernel crash/oops a realistic impact.

* Weak LPE concern: +1 paranoid only
  The stale object may survive into `file->private_data` if the race is won in a bad state, so further file operations could dereference freed or reused memory. No controlled reclaim or write primitive is demonstrated, so this remains weak and manual-review oriented.

* Privileged/device-management lifetime path: +1
  VDUSE is a device-management path tied to vDPA/userspace device backends. Corruption occurs in a trusted kernel object lifecycle path.

* Hard or unreliable race: -1
  Exploitation requires racing `open()` against `VDUSE_DESTROY_DEV`.

* Rare or configuration-dependent subsystem: -1
  VDUSE is not a broad default exposure path on ordinary systems and usually requires the subsystem and device nodes to be configured.

## 3. Reachability analysis

This is a local issue. A realistic trigger needs access to the VDUSE device interface and the ability to race device open with device destruction. In many default deployments this likely requires privileged setup or access granted to a virtualization or device-backend service. However, this should not automatically be treated as full PR:H because VDUSE access may be delegated to container root, a service account, or another reduced-privilege actor. There is no evidence of direct network reachability.

Call-site confidence: high. The patch shows the relevant open path, IDR lookup, lock ordering, and stale pointer window directly.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes an explicit kernel UAF in an object lifetime path. The realistic demonstrated impact is local DoS through kernel crash. The theoretical risk is higher because a stale `struct vduse_dev` pointer can be used after free, but the patch does not show attacker-controlled reclaim, callback control, arbitrary write, or reliable object replacement. Therefore the conservative score stays borderline/manual-review, while the paranoid score reaches Actionable Moderate.

## 5. One-sentence report phrase

A local race in the VDUSE open path can allow `struct vduse_dev` to be freed by `VDUSE_DESTROY_DEV` after IDR lookup but before the open path takes `dev->lock`, causing a use-after-free with realistic kernel crash impact and weak privilege-escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: explicit kernel UAF plus local race-controlled object lifetime makes this unsuitable for auto-close, even though no strong LPE primitive is demonstrated.

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

Patch: vduse: hold vduse_lock across IDR lookup in open path [ Upstream
Commit: 35483c5306e09b3190ff937089d404a78012695c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=35483c5306e09b3190ff937089d404a78012695c

Changed files:
  drivers/vdpa/vdpa_user/vduse_dev.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=35483c5306e09b3190ff937089d404a78012695c

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

The original Linux kernel CVE announcement for CVE-2026-74313 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74313

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: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).