[CVE-2026-53164][MODERATE REGULAR] iommu/dma: Do not try to iommu_map a 0 length region in swiotlb

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

CVE: CVE-2026-53164
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/dma: Do not try to iommu_map a 0 length region in swiotlb
Commit: ab61c990a87d084f5565ee70340543e3a5394697
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab61c990a87d084f5565ee70340543e3a5394697
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53164
Analysis date: Thu, 25 Jun 2026 04:53:44 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline manual review recommended / Ordinary Moderate unless deployment uses panic_on_warn or delegated storage passthrough
Manual review required: YES

Summary:
A zero length SWIOTLB middle mapping can cause iommu_map failure followed by error unwind from the wrong offset, corrupting DMA mapping state and later triggering WARN_ON during mapping destruction on affected Thunderbolt NVMe passthrough paths.

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

The original Linux kernel CVE announcement for CVE-2026-53164 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53164

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53164	MODERATE	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:L/I:L/A:H';CWE-754;CWE-755;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'A zero length middle segment in iommu_dma_iova_link_swiotlb can make the IOMMU mapping path reject an iommu_map request and then run error unwind from the wrong offset. This corrupts DMA mapping state and later triggers WARN_ON during mapping destruction. The known trigger involves forced SWIOTLB with oddly aligned buffers, often seen with some Thunderbolt NVMe drives and smartctl style passthrough commands. For the CVSS the PR:L is used in the paranoid score because a local low privileged process may be able to reach a delegated storage management path in some deployments, although reliable triggering usually needs passthrough access or device management rights. The issue is not reachable over an IP network and is local or hardware adjacent in practice. Impact is at least denial of service via WARN_ON or crash when panic_on_warn is enabled, with limited confidentiality or integrity impact kept only for paranoid triage because DMA mapping state is corrupted.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate unless deployment uses panic_on_warn or delegated storage passthrough (with actual score 3)	YES	SIMPLEFIX DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Ordinary Moderate unless deployment uses panic_on_warn or delegated storage passthrough**::

## 2. Signal breakdown

Paranoid score signals:

* +1 Firmware-mediated external influence. The known trigger involves specific Thunderbolt NVMe devices, forced SWIOTLB, and oddly aligned buffers.
* +1 Weak/indirect corruption candidate. The wrong unwind offset can corrupt DMA/IOMMU mapping bookkeeping, but the patch does not show UAF, OOB write, arbitrary write, or attacker-controlled payload.
* +1 Privileged kernel/device-management memory corruption path. The corrupted state is in the trusted IOMMU/DMA mapping path.
* +1 Availability impact realistic. The observed failure is WARN_ON during mapping destruction, with stronger DoS relevance when panic_on_warn is enabled or if the broken mapping path disrupts device I/O.
* +1 Important filesystem/storage path. The issue is in DMA mapping for storage I/O, observed with NVMe passthrough.
* -1 Corruption primitive constrained. The corruption appears to be metadata/bookkeeping state with no demonstrated attacker-controlled overwrite target or payload.

Conservative score signals:

* +1 Weak DMA mapping state corruption.
* +1 Availability concern from WARN_ON or possible panic_on_warn.
* -1 Constrained metadata-only corruption.
* -1 to -2 Typical triggering requires privileged storage passthrough or device-management access, often root or CAP_SYS_RAWIO-like privileges.

## 3. Reachability analysis

The realistic trigger is local and hardware-adjacent, not IP-network reachable. It is reported with Thunderbolt NVMe devices that force SWIOTLB and with oddly aligned passthrough buffers from smartctl-like commands. In typical deployments, issuing NVMe passthrough commands requires administrative or storage-management privileges. A paranoid interpretation keeps PR lower only for environments where storage management is delegated to a reduced-privilege service, container, or operator account.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or borderline actionable Moderate than an Important-class vulnerability. The patch describes corrupted DMA mapping state, which deserves manual attention, but it does not demonstrate a strong memory corruption primitive such as UAF, OOB write, arbitrary write, reclaim control, or page ownership violation. Realistic impact is mainly WARN_ON or local DoS, with higher concern only in panic_on_warn or delegated device-management environments.

## 5. One-sentence report phrase

A zero length SWIOTLB middle mapping can cause iommu_map failure followed by error unwind from the wrong offset, corrupting DMA mapping state and later triggering WARN_ON during mapping destruction on affected Thunderbolt NVMe passthrough paths.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the bug affects IOMMU/DMA mapping state in a storage path, but it should not be auto-escalated to Important without evidence of a concrete memory corruption primitive beyond constrained mapping bookkeeping corruption.

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

Patch: iommu/dma: Do not try to iommu_map a 0 length region in swiotlb
Commit: ab61c990a87d084f5565ee70340543e3a5394697
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab61c990a87d084f5565ee70340543e3a5394697

Commit description:

iommu_dma_iova_link_swiotlb() processes a mapping that is unaligned in three
parts, the head, middle and trailer. If the middle is empty because there
are no aligned pages it will call down to iommu_map() with a 0 size
which the iommupt implementation will fail as illegal.

It then tries to do an error unwind and starts from the wrong spot
corrupting the mapping so the eventual destruction triggers a WARN_ON.

Check for 0 length and avoid mapping and use offset not 0 as the starting
point to unlink.

This is frequently triggered by using some kinds of thunderbolt NVMe
drives that trigger forced SWIOTLB for unaligned memory. NVMe seems to
pass in oddly aligned buffers for the passthrough commands from smartctl
that hit this condition.

Cc: stable@vger.kernel.org
Fixes: 433a762 ("dma-mapping: Implement link/unlink ranges API")
Reported-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/0-v1-8536728bc89f+469-swiotlb_warn_jgg@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/dma-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=ab61c990a87d084f5565ee70340543e3a5394697

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

The original Linux kernel CVE announcement for CVE-2026-53164 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53164

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4

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).