[CVE-2026-80687][LOW] iommufd/viommu: Release the igroup lock on the vdevice_size error path

[CVE-2026-80687][LOW] iommufd/viommu: Release the igroup lock on the vdevice_size error path

[AL-KERNEL]

CVE: CVE-2026-80687
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommufd/viommu: Release the igroup lock on the vdevice_size error path
Commit: 294b464b2be7e57872864cb6936e1d9c7294f89d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=294b464b2be7e57872864cb6936e1d9c7294f89d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80687
Analysis date: Fri, 28 Aug 2026 04:10:41 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80687 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80687

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-2026-80687	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:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-703;CWE-755;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'iommufd_vdevice_alloc_ioctl() can leave the idev igroup lock held when the driver vdevice_size validation fails, because the error path jumps below the mutex unlock. A local process that can issue the vDEVICE allocation ioctl can trigger a persistent lock state for that iommufd group when the affected driver configuration reaches this guard. For the CVSS the PR:L is used because triggering requires local access to the iommufd ioctl interface, but not necessarily full host root in deployments where device access is delegated to a VM manager or service account. The issue is not network reachable and affects the control plane rather than DMA or packet processing. Impact is denial of service only through a deadlock of later vDEVICE operations on the same group, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	LOCK DEADLOCK SIMPLEFIX ERRORPATH 	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local low-privilege or delegated trigger: +1. A local process that can issue the iommufd vDEVICE allocation ioctl can reach the path, but this usually requires delegated device access or a VM management context.
* Reliable limited DoS: +1. The missed mutex_unlock() can leave the igroup lock held and deadlock later vDEVICE operations for the same group.
* Availability impact beyond a single failed ioctl: +1 in the paranoid score only. The deadlock can persist for later operations on that group, but it is not clearly host-wide.
* Hard or configuration-dependent trigger: -1. The failing branch depends on an invalid or unsupported driver vdevice_size or missing vdevice_init condition, not arbitrary normal operation.
* No memory corruption: +0. The patch fixes an error-path jump target and lock release. It does not show UAF, OOB, double free, refcount misuse, object confusion, or attacker-controlled overwrite.
* No C/I impact: +0. There is no supported confidentiality or integrity primitive.

3. Reachability analysis
The bug is locally reachable through the iommufd viommu vDEVICE allocation ioctl when the caller already has access to the relevant iommufd/device-management interface. In typical deployments this is not a remote path and is usually exercised by a VMM, management service, or delegated virtualization process rather than an arbitrary remote attacker. Namespaces or container delegation could reduce the practical privilege level to a service account or container root with device access, but the issue still does not provide a memory corruption or privilege escalation primitive. The affected feature is specific to iommufd/viommu driver-defined vDEVICE support, so exposure is narrower than common kernel syscalls or networking paths.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like local DoS issue. The realistic impact is a persistent lock state causing deadlock of later vDEVICE operations on the same group. Theoretical escalation is not supported by the patch because the primitive is a missed unlock on an error path, not memory lifetime corruption or data corruption. Conservative handling can be deferred unless the product heavily relies on delegated iommufd/viommu access from less trusted VM management components.

5. One-sentence report phrase
A missed mutex unlock in the iommufd viommu vDEVICE allocation error path can deadlock later vDEVICE operations for the same group, causing a local control-plane DoS without evidence of memory corruption or privilege escalation.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a missed-unlock error-path DoS with no UAF, OOB access, arbitrary write, sensitive-object access, network reachability, or privilege escalation evidence.

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

Patch: iommufd/viommu: Release the igroup lock on the vdevice_size error path
Commit: 294b464b2be7e57872864cb6936e1d9c7294f89d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=294b464b2be7e57872864cb6936e1d9c7294f89d

Commit description:

iommufd_vdevice_alloc_ioctl() takes idev->igroup->lock, then validates the
driver's vdevice_size against the core structure size with a WARN_ON_ONCE.
On failure that guard jumps to out_put_idev, below out_unlock_igroup, so it
skips the mutex_unlock(), leaving the igroup lock held and deadlocking the
next vDEVICE operation on that group.

Jump to out_unlock_igroup instead.

Fixes: ed42eee ("iommufd/viommu: Add driver-defined vDEVICE support")
Link: https://patch.msgid.link/r/e903f775d491296a525097e2a90b3eb6a47cf2ef.1783311134.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/iommufd/viommu.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=294b464b2be7e57872864cb6936e1d9c7294f89d

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

The original Linux kernel CVE announcement for CVE-2026-80687 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80687

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  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).