[CVE-2026-93205][MODERATE REGULAR] iommu/arm-smmu-v3: Manage teardown with devm

[CVE-2026-93205][MODERATE REGULAR] iommu/arm-smmu-v3: Manage teardown with devm

[AL-KERNEL]

CVE: CVE-2026-93205
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/arm-smmu-v3: Manage teardown with devm
Commit: 981686f4137760a16a03c5193f11d85133533f93
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=981686f4137760a16a03c5193f11d85133533f93
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93205
Analysis date: Thu, 24 Sep 2026 13:13:16 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93205 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93205

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 REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-93205	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93205 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:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'An ARM SMMU v3 teardown ordering flaw can free the IOPF queue before the event queue IRQ is released. A later event queue interrupt can then access the freed IOPF queue and cause a kernel use-after-free. Triggering requires removal reset or unbind of an ARM SMMU device while IOPF support and the relevant IRQ path are active. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over device lifecycle operations. The issue is not directly network reachable. Impact is at least a local denial of service through a kernel crash. In the worst case the confirmed kernel use-after-free may provide confidentiality or integrity impact and should be reviewed manually. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	INIT UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

The supplied patch establishes a real teardown UAF, but does not establish attacker-controlled replacement, post-free contents, repeated lifetime mutation, arbitrary read or write, privilege escalation, or a direct below-host-admin trigger.

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. `arm_smmu_device_remove()` can free `evtq.iopf` before devm releases the event queue IRQ. The commit explicitly states that the IRQ handler uses the freed IOPF queue.
* +1 Reliable kernel crash / strong DoS. A later IRQ handler access to freed kernel memory can cause an Oops or kernel crash.

Negative signals:

* No host-admin penalty applied. Device removal, reset, unbind, and the relevant IOPF setup are not fully resolved in the supplied context. Host-admin-equivalent control may be required for reliable triggering, but this is not established sufficiently to apply a negative score.
* No hard-race penalty applied. The unsafe ordering is concrete. The patch does not establish that the IRQ timing window is exceptionally narrow, externally uncontrollable, or non-repeatable.
* No rare-hardware penalty applied. ARM SMMU v3 and IOPF are platform and configuration dependent, but the supplied evidence does not establish a physical-only or genuinely rare attacker requirement.

Important non-awarded signals:

* Controlled reclaim or controlled object replacement is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Attacker-controlled post-free queue contents are not demonstrated.
* Structured stale-object exploitation leverage is not awarded. The visible evidence establishes a teardown IRQ access, but not meaningful attacker influence over reused queue fields, callbacks, pointers, offsets, or object replacement.
* Weak LPE concern is not awarded merely because the bug is a UAF.
* No additional Availability point is awarded because the same stale IRQ access already accounts for the crash or DoS consequence.
* Confidentiality and integrity points are not awarded. A UAF alone does not establish disclosure or unauthorized modification.
* The later Tegra241 CMDQV CMD_SYNC UAF mentioned in the commit message is explicitly a subsequent issue and is not scored as part of this patch.

3. Reachability analysis

The immediate vulnerable sequence is:

`arm_smmu_device_remove()`
`-> iopf_queue_free(evtq.iopf)`
`-> remove returns`
`-> devm later unwinds IRQ resources`
`-> event queue IRQ handler accesses evtq.iopf`

The visible patch does not establish that an ordinary local user can initiate the full removal or teardown sequence. Typical device unbind, reset, driver reload, and platform-device lifecycle operations are often administrative operations, but the exact interface and capability checks for this platform-specific SMMU lifecycle are not included. Therefore HostAdminRequired is UNKNOWN rather than YES.

Namespace-scoped reachability is also unresolved. The affected ARM SMMU device is platform-owned hardware state. The patch provides no evidence that a user or network namespace can create, remove, reset, or otherwise fully control the affected SMMU instance and its IRQ teardown sequence.

There is no direct network path. Firmware or device events may contribute to the IRQ timing, but no attacker-controlled firmware or external-device input path is established by the supplied evidence.

The affected path requires ARM SMMU v3 operation with an allocated IOPF queue and event queue IRQ activity. These are relevant deployment prerequisites, but they are not scored as a negative hardware penalty because the evidence does not establish that they are rare or impossible for a relevant attacker environment.

4. Primitive and severity interpretation

The exact primitive is a real post-free access to an `iopf_queue` from an event queue IRQ handler after `arm_smmu_device_remove()` frees that queue. This is a kernel lifetime violation and therefore CLASS_B.

The stale object is an active queue used by IRQ processing, but the demonstrated stale use occurs in a teardown ordering path. The patch does not show that an attacker can reclaim the freed queue with attacker-shaped data, force a replacement object at the same address, control fields consumed by the IRQ handler after reuse, or cause a callback or function pointer dispatch.

This is not a repeated release or refcount case. The patch does not show a first `put` followed by a second lifetime-mutating `put`, free, or refcount operation on the same dangling reference. Therefore the concrete repeated release or refcount signal and the related FLOOR 5 rule do not apply.

The demonstrated consequence is kernel crash or denial of service. A stronger confidentiality, integrity, or privilege-escalation consequence is theoretically possible for some kernel UAF classes, but it is not supported by a concrete mechanism in the supplied patch. The issue should receive manual review because it is a real IRQ-context UAF in IOMMU driver state, but it is not currently a strong Important candidate.

AutoDowngradeAllowed is YES because the available evidence supports a constrained teardown UAF with crash or DoS impact and does not establish meaningful unresolved exploitation leverage beyond the stale dereference.

5. One-sentence report phrase

An ARM SMMU v3 teardown ordering flaw can free an IOPF queue before its event queue IRQ handler is released, allowing a later IRQ to access freed memory and cause a local kernel crash or denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the patch directly establishes a kernel IRQ-context use-after-free, but the supplied context does not establish attacker-controlled reuse, arbitrary memory access, a below-host-admin trigger, or a practical privilege-escalation path.

7. Call-site confidence

Call-site confidence: medium

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

Patch: iommu/arm-smmu-v3: Manage teardown with devm
Commit: 981686f4137760a16a03c5193f11d85133533f93
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=981686f4137760a16a03c5193f11d85133533f93

Commit description:

arm_smmu_device_remove() manually frees the IOPF queue, destroys the
vmid_map and disables the device, while the IRQs and queues are devm
managed. devm unwinds only after remove() returns, so the cleanup runs
in the wrong order. The IOPF queue is freed before the event-queue IRQ
whose handler uses it.

Manage all of it with devm so the unwind order is correct. Free the IOPF
queue and vmid_map via devm actions, and disable the device from one
registered after arm_smmu_device_reset().

This is also a prerequisite for fixing a Tegra241 CMDQV CMD_SYNC
use-after-free in the subsequent patch.

Cc: stable@vger.kernel.org
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.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=981686f4137760a16a03c5193f11d85133533f93

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

The original Linux kernel CVE announcement for CVE-2026-93205 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93205

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 3

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 REGULAR

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).