[CVE-2026-80818][MODERATE 7.0] iommu/tegra241-cmdqv: Fix CMD_SYNC use-after-free on teardown

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

CVE: CVE-2026-80818
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: iommu/tegra241-cmdqv: Fix CMD_SYNC use-after-free on teardown
Commit: d2ab08437e913d9e4dda4dfd0d327446ec8717fc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d2ab08437e913d9e4dda4dfd0d327446ec8717fc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80818
Analysis date: Fri, 04 Sep 2026 14:53:59 -0400
ActionableScore: 6
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A CMD_SYNC use-after-free in the Tegra241 CMDQV teardown path can occur when VINTF deinit issues commands after the SMMU command queue has been freed, causing a local kernel crash and requiring manual review because the affected path is a privileged IOMMU lifetime-management bug.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80818 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80818

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-2026-80818	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80818 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:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'CMD_SYNC use-after-free can occur in the Tegra241 CMDQV teardown path because VINTF deinit may issue a command after the SMMU command queue has already been freed during devres unwind or device unbind. This can lead to an invalid access in arm_smmu_cmdq_issue_cmdlist and crash the kernel. For the CVSS the PR:L is used for the paranoid score because the iommufd viommu destroy path and delegated device management can be reachable by a local VMM or service account with limited device access rather than full host admin rights. The issue is not network reachable and requires local device or virtualization control on systems with Tegra241 CMDQV support. Impact is at least local denial of service and in worst case may allow confidentiality or integrity impact due to a kernel use-after-free memory corruption scenario.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) 	MAYBE	READ OOB INIT ERRORPATH UAF HARDWARE TEST  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The commit explicitly describes a CMD_SYNC issued through an already freed SMMU command queue, which is a use-after-free condition.
* Real lifetime corruption: +1. The bug is caused by teardown ordering where the queue lifetime ends before VINTF deinit still uses it.
* Reliable kernel crash / strong DoS: +1. The provided trace shows an Oops in arm_smmu_cmdq_issue_cmdlist.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in an IOMMU/SMMU device-management teardown path.
* Requires admin/root/CAP_* in typical deployments: -2. Probe failure, driver unbind, and device-management teardown are normally privileged.
* Rare hardware/configuration exposure: -1. This is specific to Tegra241 CMDQV / ARM SMMU v3 deployments.

Paranoid additions / refinements:

* Firmware-mediated external influence: +1. The demonstrated failure depends on VCMDQ enable/reset failure, which may be influenced by firmware/device state rather than ordinary packet or syscall input.
* Local delegated trigger concern: +1. The commit notes that tegra241_cmdqv_remove_vintf() is also used by the iommufd viommu destroy path, so a local VMM or reduced-privilege device-management service may be closer to PR:L than full host-root.
* Weak LPE concern: +1. This is not just a NULL dereference. It is a UAF in a privileged IOMMU command path, and issuing CMD_SYNC on freed memory is a plausible corruption sink, although no attacker-controlled reclaim or overwrite primitive is demonstrated.

## 3. Reachability analysis

The most realistic trigger is local and device-management related: failed probe unwind, live unbind, or iommufd viommu destruction on systems with Tegra241 CMDQV support. In normal deployments, probe/unbind paths require administrator-level control, but the iommufd viommu destroy path makes delegated virtualization or VMM service-account exposure relevant. This is not network reachable. Containers or namespaces only matter if they are delegated access to the relevant VFIO/iommufd/IOMMU device-management interface. The path is hardware-specific and not broadly default-exposed across generic Linux systems.

Call-site confidence: high, because the patch and commit message include the teardown call path, the crash trace, and the iommufd viommu destroy path reference.

## 4. Severity interpretation

This is stronger than an ordinary Moderate crash because the root cause is a real use-after-free in a privileged IOMMU command queue teardown path. Realistic demonstrated impact is local DoS via kernel crash. Practical privilege escalation is not demonstrated, because there is no shown attacker-controlled reclaim, object replacement, arbitrary write, callback control, or refcount takeover. The paranoid score treats the UAF and iommufd/device-management context as requiring manual review, but does not assume reliable LPE.

## 5. One-sentence report phrase

A CMD_SYNC use-after-free in the Tegra241 CMDQV teardown path can occur when VINTF deinit issues commands after the SMMU command queue has been freed, causing a local kernel crash and requiring manual review because the affected path is a privileged IOMMU lifetime-management bug.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a confirmed UAF in a security-sensitive IOMMU/device-management path, and the iommufd viommu destroy reference makes reduced-privilege virtualization exposure plausible enough to avoid auto-closing.

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

Patch: iommu/tegra241-cmdqv: Fix CMD_SYNC use-after-free on teardown
Commit: d2ab08437e913d9e4dda4dfd0d327446ec8717fc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d2ab08437e913d9e4dda4dfd0d327446ec8717fc

Commit description:

arm_smmu_impl_remove() is registered as a devres action in
arm_smmu_impl_probe(), before arm_smmu_init_queues() allocates
smmu->cmdq.q.base. On a devres unwind, whether a failed probe or an
unbind, the queue is freed first and arm_smmu_impl_remove() then runs
tegra241_cmdqv_remove_vintf(), whose VINTF deinit issues a CMD_SYNC on
the freed memory.

Observed during testing with a QEMU hack that makes the VCMDQ fail to
enable, so the impl reset fails and probe aborts into the devres unwind:

 platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: failed to enable, STATUS=0x00000000
 platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: GERRORN=0x0, GERROR=0x4, CONS=0x0
 platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: uncleared error detected, resetting
 arm-smmu-v3 arm-smmu-v3.0.auto: failed to reset impl
 arm-smmu-v3 arm-smmu-v3.0.auto: probe with driver arm-smmu-v3 failed with error -110
 Unable to handle kernel paging request at virtual address ffff8000891e0098
 ...
 Internal error: Oops: 0000000096000047 [#1] SMP
 ...
 Call trace:
  arm_smmu_cmdq_issue_cmdlist+0x320/0x6fc (P)
  tegra241_vcmdq_hw_deinit+0x98/0x168
  tegra241_vintf_hw_deinit+0x5c/0x1b0
  tegra241_cmdqv_remove_vintf+0x34/0xec
  tegra241_cmdqv_remove+0x40/0x9c
  arm_smmu_impl_remove+0x20/0x30
  devm_action_release+0x14/0x20
  devres_release_all+0xa8/0x110
  device_unbind_cleanup+0x18/0x84
  really_probe+0x1f0/0x29c

Drop the VINTF deinit from tegra241_cmdqv_remove_vintf() so the unwind no
longer touches the freed queue. Quiesce the VINTFs earlier instead. Add a
device_disable() impl op and run it from arm_smmu_disable_action() while
the CMDQ is still up. That handles a live unbind. A failed reset is already
handled because tegra241_vintf_hw_init() deinits the VINTF on its own error
path. tegra241_cmdqv_remove_vintf() is also used by the iommufd viommu
destroy path, so quiesce there too.

Fixes: 4dc0d12 ("iommu/tegra241-cmdqv: Add user-space use support")
Cc: stable@vger.kernel.org
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
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
  drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.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=d2ab08437e913d9e4dda4dfd0d327446ec8717fc

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

The original Linux kernel CVE announcement for CVE-2026-80818 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80818

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: 3
  Paranoid ActionableScore: 6

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).

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