[CVE-2026-74277][MODERATE 7.0] iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path [ Upstream

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

CVE: CVE-2026-74277
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path [ Upstream
Commit: 8646f00ce021e49f4f05bc1d4060a0c27b25d0e1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8646f00ce021e49f4f05bc1d4060a0c27b25d0e1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74277
Analysis date: Sat, 15 Aug 2026 13:58:14 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74277 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74277

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: NO

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-2026-74277	MODERATE	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-805;CWE-682;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A wrong DMA length assignment in the PCI P2PDMA path can make each current scatterlist segment inherit the length of the first segment instead of its own length. In multi segment scatterlists this may corrupt DMA descriptors and can cause a device to read or write beyond the intended P2PDMA segment or to transfer incomplete data. For the CVSS the PR:L value is used because reliable triggering may only require a local user or process able to submit I/O through an already configured P2PDMA capable stack, not full administrative control. The issue is not directly network reachable from the patch context. Impact is at least local denial of service or data corruption, and in the paranoid case may include confidentiality and integrity impact because corrupted DMA lengths can plausibly affect memory or peer device data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DANGER SIMPLEFIX DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

2. Signal breakdown
* Local unprivileged trigger: +1. If a P2PDMA capable stack is already configured, a local process able to submit relevant I/O may reach the affected DMA mapping path without full host root.
* Memory corruption, weak/indirect corruption candidate: +1. The bug corrupts DMA length metadata for scatterlist entries, but the patch does not show attacker-controlled target selection or payload control.
* Privileged kernel/device-management memory corruption path: +1. The corrupted value is used in a DMA/IOMMU adjacent path, which is a trusted kernel/device boundary.
* Important filesystem/storage path: +1. P2PDMA is commonly relevant to storage or accelerator data paths, and incorrect DMA lengths may corrupt transferred data.
* Reliable kernel crash / strong DoS: +1 in paranoid scoring. Incorrect DMA lengths can plausibly cause device errors, I/O failure, or kernel/device instability.
* Integrity impact plausible: +1 in paranoid scoring. A wrong DMA segment length may cause incomplete or excessive transfers and corrupt peer-device or storage data.
* Confidentiality impact plausible: +1 in paranoid scoring. Overlong DMA reads may expose adjacent peer-memory or unintended device data, but this is not demonstrated.
* Rare AND difficult-to-reach subsystem/configuration: -1. PCI P2PDMA is not a default generic I/O path and requires suitable hardware and configuration.
* Hard or unreliable conditions: -1. Triggering requires multi-segment scatterlists in the P2PDMA path with segment lengths differing from the first entry.
* No attacker-controlled payload or overwrite target: -1 conservative. The wrong value is derived from another scatterlist length, not an arbitrary attacker-chosen kernel pointer or payload.

3. Reachability analysis
The most realistic trigger is local or workload-mediated I/O through an already configured PCI P2PDMA-capable path. This does not appear directly network reachable from the patch context. Namespaces or containers may matter only if they can access a device or storage service that submits P2PDMA I/O on their behalf. The path is hardware and configuration dependent, so exposure is narrower than ordinary block I/O, but the affected code sits in a sensitive DMA mapping layer. Call-site confidence: medium, because the changed helper context is shown but the higher-level P2PDMA users are not included in the patch input.

4. Severity interpretation
This is more than an ordinary typo because it corrupts DMA descriptor length metadata in a trusted IOMMU/DMA path. Conservative handling is borderline manual review because practical exploitability depends on rare P2PDMA conditions and attacker control appears limited. Paranoid handling reaches Actionable Moderate because DMA length corruption can plausibly cause data corruption, device instability, or unintended peer-memory access, even though the patch does not prove a strong LPE primitive. It should not be treated as a confirmed Important vulnerability without call-path validation.

5. One-sentence report phrase
A wrong scatterlist DMA length assignment in the PCI P2PDMA path can corrupt multi-segment DMA mappings, potentially causing I/O data corruption, device instability, or kernel DoS under specialized P2PDMA configurations.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. This should not be auto-closed because it affects DMA length metadata in a storage/device path, but the final severity depends on whether reachable P2PDMA call sites allow unprivileged or remotely mediated I/O to create affected multi-segment scatterlists.

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

Patch: iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path [ Upstream
Commit: 8646f00ce021e49f4f05bc1d4060a0c27b25d0e1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8646f00ce021e49f4f05bc1d4060a0c27b25d0e1

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=8646f00ce021e49f4f05bc1d4060a0c27b25d0e1

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

The original Linux kernel CVE announcement for CVE-2026-74277 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74277

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: 4
  Paranoid ActionableScore: 5

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 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).

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).