[CVE-2026-74520][IMPORTANT] iommu/iommufd: Fix IOPF group ownership UAF

[CVE-2026-74520][IMPORTANT] iommu/iommufd: Fix IOPF group ownership UAF

[AL-KERNEL]

CVE: CVE-2026-74520
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: iommu/iommufd: Fix IOPF group ownership UAF
Commit: 6da8f37419dd4c456f26fc203f04e000186f4b3d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6da8f37419dd4c456f26fc203f04e000186f4b3d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74520
Analysis date: Sat, 15 Aug 2026 14:08:59 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74520 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74520

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: IMPORTANT
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-2026-74520	IMPORTANT	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-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An IOMMUFD IOPF group ownership bug can leave the same iopf_group linked in both the generic IOPF pending list and the IOMMUFD deliver list. If a device is detached or a HWPT is replaced while an accepted fault group is still tracked this way, iopf_queue_remove_device can free the group through the generic pending list while IOMMUFD still retains references in the deliver list or response xarray. A later read, response, or cleanup can then access the freed group, creating a kernel use-after-free condition. For the CVSS the PR:L is used for the paranoid score because triggering requires local access to IOMMUFD and a device or VM setup that can generate I/O page faults, but this is not necessarily full host administrator control in delegated VFIO or containerized service deployments. The issue is not directly network reachable and depends on IOPF capable hardware and IOMMUFD usage. Impact is at least local denial of service via kernel crash and in the worst defensible case may allow confidentiality or integrity impact due to kernel use-after-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	LOCK INIT UAF HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Local low-privilege trigger: +1. Triggering requires local access to IOMMUFD/VFIO/device-assignment style functionality, but this may be delegated to VM or container management contexts and is not necessarily full host-root control.
* Memory corruption, strong primitive: +2. The commit explicitly describes a use-after-free of `iopf_group`.
* Real lifetime corruption: +1. The same group can remain owned by both the generic IOPF pending list and the IOMMUFD deliver/response structures, allowing one owner to free it while another still references it.
* Reliable kernel crash / strong DoS: +1. Later read, response, or cleanup can access the freed group.
* Privileged kernel/device-management memory corruption path: +1. The bug is in IOMMUFD/IOPF device fault handling, a security-sensitive device-management path.
* Weak LPE concern, paranoid only: +1. Kernel UAF in IOMMUFD can plausibly exceed DoS, but no controlled reclaim, overwrite, callback hijack, or type confusion is shown.
* Rare/config-dependent exposure: -1. Requires IOMMUFD, IOPF-capable device behavior, and detach or HWPT replacement timing.

3. Reachability analysis
A local actor with access to IOMMUFD/VFIO-style device assignment and a device setup capable of generating I/O page faults is the realistic trigger. This is not network reachable. In typical deployments, setup may be controlled by root or a VM manager, but delegated virtualization, containerized device-management services, or reduced-capability service accounts can make PR:L more appropriate than PR:H. The path is not default for ordinary desktop/server workloads, but it is relevant in virtualization and device-passthrough environments.

4. Severity interpretation
This is not an ordinary Moderate cleanup issue because the patch fixes a concrete kernel UAF caused by split ownership of the same fault group. Realistic evidence supports local DoS and manual review. Privilege escalation is not demonstrated, but the UAF occurs in a sensitive IOMMUFD lifetime path, so the paranoid score treats it as Actionable Moderate and an Important candidate for review rather than auto-close.

5. One-sentence report phrase
An IOMMUFD IOPF group ownership bug can leave a freed fault group reachable through IOMMUFD deliver or response structures after device detach or HWPT replacement, causing a local kernel UAF with DoS impact and plausible privilege escalation concern.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is a concrete kernel use-after-free in a device-management and IOMMUFD path, with enough lifetime and ownership complexity to require human review.

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

Patch: iommu/iommufd: Fix IOPF group ownership UAF
Commit: 6da8f37419dd4c456f26fc203f04e000186f4b3d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6da8f37419dd4c456f26fc203f04e000186f4b3d

Commit description:

iopf_group_alloc() links each last-page IOPF group into the generic IOPF
pending list before invoking the domain fault handler.
iommufd_fault_iopf_handler() also queued an accepted group in the
IOMMUFD deliver list without removing it from the generic pending list.

When detach or HWPT replacement drops the device's IOPF reference count
to zero, an IOMMU driver may call iopf_queue_remove_device(). That
function responds to and frees groups through the generic pending list
without removing the same groups from IOMMUFD's deliver list or response
xarray. A later read, response, or cleanup can then access the freed
group and cause a UAF.

Fix this by dequeuing an accepted group from the generic pending list
before IOMMUFD queues it for userspace response.
Make iopf_group_response() send a response regardless of pending-list
membership, so the dequeued group can still be completed by IOMMUFD.

Link: https://patch.msgid.link/r/3CFD314D0FE4D7EC+20260720085017.3998878-2-peiyang_he@smail.nju.edu.cn
Closes: https://lore.kernel.org/all/B4F28798E2E784CA+d29f723c-b2b5-4b67-8d1c-4f7b9b0b27cb@smail.nju.edu.cn/
Fixes: 34765cb ("iommufd: Associate fault object with iommufd_hw_pgtable")
Cc: stable@vger.kernel.org
Tested-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/io-pgfault.c
  drivers/iommu/iommufd/eventq.c
  include/linux/iommu.h

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=6da8f37419dd4c456f26fc203f04e000186f4b3d

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

The original Linux kernel CVE announcement for CVE-2026-74520 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74520

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:L/I:L/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: 5
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).