[CVE-2026-89447][LOW] iommufd: Avoid locking internal accesses during unmap

[CVE-2026-89447][LOW] iommufd: Avoid locking internal accesses during unmap

[AL-KERNEL]

CVE: CVE-2026-89447
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommufd: Avoid locking internal accesses during unmap
Commit: 436189ee4bb2c7c993b945d68570dd38c3e4349e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=436189ee4bb2c7c993b945d68570dd38c3e4349e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89447
Analysis date: Fri, 11 Sep 2026 18:23:45 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89447 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89447

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-2026-89447	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89447 CHECK WITH IMPACT FROM ORIG NN LOW	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-772;CWE-911;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'iommufd_access_notify_unmap() could leak an object reference because internal access entries were locked before the code checked whether they should be skipped. When iommufd_lock_obj() succeeded for an internal access, the loop continued without the matching object put used by the normal unmap path, leaving the reference held. For the CVSS the PR:L is used because reliable triggering requires a local process with access to the iommufd or device assignment control path, but this may be delegated to a service account or virtualization user rather than full host root. The issue is not network reachable and does not provide a demonstrated memory corruption primitive. Impact is resource exhaustion and local denial of service, with the paranoid score raising availability to high only for sustained abuse.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	LOCK SIMPLEFIX LEAK HARDWARE TEST  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. `iommufd_lock_obj()` can take an object reference for an internal access, then the loop skips it without the matching `iommufd_put_object()`.
* Paranoid only: +1 Sustained resource exhaustion concern. Repeated unmap notification activity could accumulate leaked references and keep objects alive, potentially causing resource pressure or cleanup failure over time.

Negative or non-awarded signals:

* RealUAF not awarded. The bug leaks a reference and prevents normal release, but does not establish use of an object after its lifetime ended.
* Concrete repeated release/refcount not awarded. This is a missing put after get/lock, not a second put on a potentially dangling reference.
* Reliable kernel crash not awarded. The patch establishes a reference leak, not an immediate panic, Oops, or fatal stale dereference.
* C/I impact not awarded. No information disclosure, unauthorized modification, arbitrary write, controlled reclaim, or security-boundary bypass is shown.
* Remote reachability not awarded. The path is local iommufd/IOMMU device-management related, not network reachable.
* Host-admin penalty not applied. Host-admin-equivalent privilege is not positively established from the supplied evidence.
* Strong resource-exhaustion escalation not awarded conservatively. A single or few operations are not shown to cause host-wide failure.

3. Reachability analysis

The reachable actor is a local process interacting with the iommufd or device-assignment control path. The exact privilege boundary is not fully established from the supplied patch alone. It may involve a virtualization stack, service account, delegated device-assignment workflow, or host administrator, but the supplied evidence does not prove host-admin-equivalent privilege for the complete trigger.

The operation is not network reachable. No namespace-scoped capability path is established, and there is no evidence that an attacker can perform the full trigger using only attacker-created namespaces. Prior setup may be needed in practical deployments, such as availability of iommufd and configured IOMMU/device-assignment infrastructure, but this is not enough to score it as host-admin-only.

No special race is required. The issue is an ordered control-flow bug: internal accesses are locked before being skipped.

4. Primitive and severity interpretation

The exact primitive is a persistent object reference leak caused by taking a reference through `iommufd_lock_obj()` before checking `iommufd_access_is_internal()`. Internal accesses are supposed to be skipped because they do not have an external unmap callback, but in the vulnerable ordering they can still be locked and then skipped without the matching put.

This is not active structured UAF and not fixed stale storage. It is a resource/lifetime accounting leak. No object is shown to be used after free, no second lifetime mutation through a dangling reference exists, and no controlled corruption or callback path is established.

PrimitiveClass is NONE because there is no demonstrated corruption, UAF, authorization bypass, COW violation, semantic reinterpretation, or similar Important-preserving primitive. The demonstrated consequence is resource leakage. The speculative consequence is local DoS through sustained accumulation, but no stronger exploitation leverage is supported.

ImportantCandidate is NO because the patch supports a leak/resource-exhaustion issue only. AutoDowngradeAllowed is YES because no unresolved memory-corruption, repeated refcount mutation, boundary bypass, or privilege-escalation primitive remains.

Likely operational severity is Low to ordinary Moderate.

5. One-sentence report phrase

A local iommufd unmap notification path can leak object references for internal access entries because they are locked before being skipped, causing potential resource exhaustion under sustained abuse but no demonstrated UAF, memory corruption, privilege escalation, or network exposure.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a concrete reference leak with possible sustained local DoS, but the patch does not establish UAF, repeated release, memory corruption, authorization bypass, or a network reachable attack surface.

7. Call-site confidence

Call-site confidence: high

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

Patch: iommufd: Avoid locking internal accesses during unmap
Commit: 436189ee4bb2c7c993b945d68570dd38c3e4349e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=436189ee4bb2c7c993b945d68570dd38c3e4349e

Commit description:

iommufd_access_notify_unmap() skips internal accesses because they do
not have an external unmap callback to invoke.

However, the current test calls iommufd_lock_obj() before checking
whether the access is internal. If iommufd_lock_obj() succeeds, the loop
then sees the internal access and continues, bypassing the matching
iommufd_put_object() used by the normal unmap path. This leaks the
object reference taken by iommufd_lock_obj().

Check for internal accesses first so skipped entries are never locked.

Fixes: 27b77ea ("iommufd/access: Bypass access->ops->unmap for internal use")
Cc: stable@vger.kernel.org
Assisted-by: Qoder:Qwen-3.8-MAX-Preview
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/iommufd/device.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=436189ee4bb2c7c993b945d68570dd38c3e4349e

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

The original Linux kernel CVE announcement for CVE-2026-89447 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89447

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  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: 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).