[CVE-2026-52952][IMPORTANT] iommu: Fix WARN_ON in __iommu_group_set_domain_nofail() due to reset

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

CVE: CVE-2026-52952
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: iommu: Fix WARN_ON in __iommu_group_set_domain_nofail() due to reset
Commit: 8fc289e809f3eb7e36cadc4684ab6fad747a5a93
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fc289e809f3eb7e36cadc4684ab6fad747a5a93
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52952
Analysis date: Fri, 26 Jun 2026 10:24:18 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in IOMMU domain recovery can leave `group->domain` pointing to a freed domain during nofail teardown, allowing a later reset completion path to reuse the stale pointer and potentially cause a kernel crash or worse device isolation impact.

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

The original Linux kernel CVE announcement for CVE-2026-52952 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52952

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
======================================================================

CVE-2026-52952	IMPORTANT	CHECK	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-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free risk exists in the IOMMU group domain recovery path because nofail domain transitions could be rejected while a domain is being torn down. If group domain still points to a domain that is freed, pci_dev_reset_iommu_done may later re attach that stale pointer during reset completion. For the CVSS the PR:L is used because a local user or service with delegated access to VFIO or IOMMU backed PCI device control may be able to reach reset and domain transition paths without full host root. The issue is not network reachable and requires local interaction with device ownership or recovery paths. Impact is at least local denial of service via kernel crash. In the worst still defensible case, the stale domain pointer is a UAF primitive in IOMMU core state and may allow confidentiality or integrity impact or privilege escalation, so CIA:HHH is used for the paranoid score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	LOCK UAF DMAorINTERRUPT HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* **Local unprivileged or delegated trigger: +1**
  Realistic triggering likely requires local interaction with VFIO, PCI reset, IOMMU ownership, or a service managing assigned devices. This is not remote, but it may be reachable by a reduced privilege VM or device-management process.

* **Memory corruption, strong corruption primitive: +2**
  The commit explicitly states that `pci_dev_reset_iommu_done()` could trigger a UAF when re-attaching `group->domain`.

* **Real lifetime corruption: +1**
  The bug is a stale pointer lifetime issue where `group->domain` may still reference a domain that is being freed in nofail teardown paths.

* **Reliable kernel crash / strong DoS: +1**
  The observed symptom includes a WARN in a nofail path, and the described UAF can plausibly lead to kernel crash or host instability.

* **Privileged kernel/device-management memory corruption path: +1**
  The corruption occurs in IOMMU core domain management, a highly trusted device and DMA control path.

* **Weak LPE concern in paranoid score: +1**
  A stale IOMMU domain pointer is not just a NULL dereference. In the worst defensible interpretation, reuse of freed IOMMU domain state could affect device DMA isolation or domain attachment semantics. No reliable reclaim or overwrite primitive is shown, so this is weak LPE concern, not strong LPE plausibility.

* **Hard or timing-dependent recovery window: -1**
  The bug depends on reset or recovery overlap with nofail domain transitions, so it is not a simple deterministic syscall-only trigger.

## 3. Reachability analysis

The issue is not network reachable. Triggering requires local access to a path that can cause PCI device reset or IOMMU domain transitions, most plausibly through VFIO, device assignment, or privileged device-management services. In typical deployments full setup of such devices is administrative, but the actual reset or recovery trigger may be reachable by a VM process, container root with delegated device access, or a service account with reduced capabilities. Namespaces do not generally make IOMMU management freely available, but delegated VFIO or device access can lower the practical privilege requirement below full host root.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch context explicitly identifies a UAF in IOMMU core state. Realistic exploitation evidence mainly supports local DoS or host instability. Theoretical escalation is plausible enough for manual review because stale IOMMU domain reuse may affect DMA isolation and trusted device state, but the patch does not demonstrate attacker-controlled reclaim, arbitrary write, or a reliable LPE primitive. Therefore the conservative score is Actionable Moderate, while the paranoid score reaches Strong Important candidate.

## 5. One-sentence report phrase

A race in IOMMU domain recovery can leave `group->domain` pointing to a freed domain during nofail teardown, allowing a later reset completion path to reuse the stale pointer and potentially cause a kernel crash or worse device isolation impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

The patch explicitly describes a possible UAF in IOMMU core domain state, and the affected path is security-sensitive because it controls device ownership and DMA isolation.

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

Patch: iommu: Fix WARN_ON in __iommu_group_set_domain_nofail() due to reset
Commit: 8fc289e809f3eb7e36cadc4684ab6fad747a5a93
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fc289e809f3eb7e36cadc4684ab6fad747a5a93

Commit description:

In __iommu_group_set_domain_internal(), concurrent domain attachments are
rejected when any device in the group is recovering. This is necessary to
fence concurrent attachments to a multi-device group where devices might
share the same RID due to PCI DMA alias quirks, but triggers the WARN_ON in
__iommu_group_set_domain_nofail().

Other IOMMU_SET_DOMAIN_MUST_SUCCEED callers in detach/teardown paths, such
as __iommu_group_set_core_domain and __iommu_release_dma_ownership, should
not be rejected, as the domain would be freed anyway in these nofail paths
while group->domain is still pointing to it. So pci_dev_reset_iommu_done()
could trigger a UAF when re-attaching group->domain.

Honor the IOMMU_SET_DOMAIN_MUST_SUCCEED flag, allowing the callers through
the group->recovery_cnt fence, so as to update the group->domain pointer.
Instead add a gdev->blocked check in the device iteration loop, to prevent
any concurrent per-device detachment.

Fixes: c279e83 ("iommu: Introduce pci_dev_reset_iommu_prepare/done()")
Cc: stable@vger.kernel.org
Closes: https://sashiko.dev/#/patchset/20260407194644.171304-1-nicolinc%40nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/iommu.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=8fc289e809f3eb7e36cadc4684ab6fad747a5a93

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

The original Linux kernel CVE announcement for CVE-2026-52952 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52952

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: 6
  Paranoid ActionableScore: 7

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).