[CVE-2026-64149][LOW] dma-mapping: move dma_map_resource() sanity check into debug code [ Upstream

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

CVE: CVE-2026-64149
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dma-mapping: move dma_map_resource() sanity check into debug code [ Upstream
Commit: 181e67bc11c5ec5b87c6c512c2078752b23ca8d4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=181e67bc11c5ec5b87c6c512c2078752b23ca8d4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64149
Analysis date: Sun, 19 Jul 2026 18:52:07 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64149 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64149

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64149	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';CWE-754;CWE-703;CWE-682;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '2.3';DESCR 'dma_map_resource() could falsely reject valid MMIO mappings because the debug sanity check used pfn_valid() as if it proved that a physical address was normal RAM. On ARM64 SPARSEMEM systems an MMIO address can share a sparsemem section with RAM and therefore have a valid PFN, which can trigger a warning and return DMA_MAPPING_ERROR. The practical impact is limited availability loss such as a driver probe failure for affected hardware and debug configurations. For the CVSS the PR:H is used because reliable triggering normally requires privileged control over driver probing, device configuration, or kernel debug conditions. The issue is not network reachable and there is no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0)  SKIP CVE-2026-64149 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: f7326196a781622b33bfbdabb00f5e72b5fb5679 YES  NO NO unknown 	MAYBE	OOB DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=0

1. **ActionableScore**
* Conservative score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate / Low-like**

2. **Signal breakdown**
* Availability impact realistic: +1. The bug can cause `dma_map_resource()` to return `DMA_MAPPING_ERROR`, leading to driver probe failure on affected hardware.
* Requires admin/root/CAP_* or privileged device/probe context: -2. Reliable triggering normally depends on driver probing, device setup, kernel configuration, or platform state, not an unprivileged user interface.
* Legacy / non-default execution mode: -1. The blocking failure requires `CONFIG_DMA_API_DEBUG`.
* Physical-only or rare hardware/platform condition: -2. The described failure depends on ARM64 SPARSEMEM section layout and MMIO sharing a sparsemem section with RAM.
* No memory corruption signal: +0. The patch removes a false-positive sanity check and moves it to debug reporting. It does not show UAF, OOB access, double free, stale pointer use, arbitrary write, or page ownership corruption.
* No confidentiality or integrity impact: +0. There is no disclosure path or attacker-controlled modification of protected data.
* Call-site confidence: high. The changed function and direct consequence are visible: the old check returned `DMA_MAPPING_ERROR`, while the new code only reports via DMA debug.

3. **Reachability analysis**
The issue is triggered through privileged kernel driver/device initialization paths using `dma_map_resource()` for MMIO resources. It is not network reachable and not exposed through a normal unprivileged local syscall path. Namespaces or containers do not materially lower the privilege requirement because the relevant resource mapping and driver probe behavior remain host-kernel/device-management operations. Realistic impact is limited to affected platforms and debug configurations, such as the Raspberry Pi 4 example in the commit message.

4. **Severity interpretation**
This behaves like a low-severity correctness and availability issue, not an actionable memory-corruption CVE. The realistic consequence is a warning plus device probe failure or loss of availability for a specific driver/device. The theoretical concern mentioned in the commit about mapping real RAM as MMIO is diagnostic context, but the actual fixed bug is a false positive that blocks valid MMIO mappings. There is no supported privilege escalation, confidentiality impact, integrity impact, or remotely reachable attack path.

5. **One-sentence report phrase**
A false-positive `pfn_valid()` sanity check in `dma_map_resource()` could reject valid MMIO mappings on ARM64 SPARSEMEM systems with DMA API debug enabled, causing limited device availability impact such as driver probe failure.

6. **Manual review recommendation**
NO MANUAL CHECK NEEDED

The issue can be auto-closed for security triage unless the affected product treats device probe failure on the specific hardware/debug configuration as operationally critical.

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

Patch: dma-mapping: move dma_map_resource() sanity check into debug code [ Upstream
Commit: 181e67bc11c5ec5b87c6c512c2078752b23ca8d4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=181e67bc11c5ec5b87c6c512c2078752b23ca8d4

Changed files:
  kernel/dma/debug.c
  kernel/dma/mapping.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=181e67bc11c5ec5b87c6c512c2078752b23ca8d4

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

The original Linux kernel CVE announcement for CVE-2026-64149 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64149

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.3

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: unknown
  Paranoid ActionableScore: 0

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).