* [CVE-2026-90388][MODERATE REGULAR] iommu/dma: Check atomic pool allocation result directly [ Upstream
@ 2026-09-18 1:38 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 1:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90388
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/dma: Check atomic pool allocation result directly [ Upstream
Commit: ac9cd0a669b8be5d178dbd471b0d68039dac58b5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac9cd0a669b8be5d178dbd471b0d68039dac58b5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90388
Analysis date: Thu, 17 Sep 2026 21:38:19 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90388 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90388
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90388 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90388 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:L/I:L/A:H';CWE-252;CWE-824;**CWE-476;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'The non blocking non coherent IOMMU DMA allocation path could treat dma_alloc_from_pool failure as success because it checked cpu_addr instead of the returned page. If the pool allocation fails and cpu_addr is not a reliable NULL indicator, iommu_dma_alloc may continue with a NULL page and use it for page_to_phys before creating an IOMMU mapping. This can cause a kernel crash and may also create limited risk around invalid DMA mapping state, but the patch does not show an arbitrary write or proven privilege escalation primitive. For the CVSS the PR:L is used because a local user or local process normally needs access to a device or driver path that can request this DMA allocation and create atomic pool pressure. The issue is not directly network reachable. Impact is at least local denial of service, with limited confidentiality or integrity impact kept only in the paranoid score for manual review sensitivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES LOCK SIMPLEFIX HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3. No floor or cap applied.
* Raw paranoid score: 4
* Paranoid score: 4. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
Conservative signals:
* +1 Weak or indirect corruption candidate. The non-blocking non-coherent DMA allocation path could treat dma_alloc_from_pool() failure as success because it checked cpu_addr instead of the returned page.
* +1 Reliable kernel crash or strong DoS concern. If page is NULL and the code continues, page_to_phys(page) and the following IOMMU mapping path can operate on an invalid page pointer.
* +1 Sensitive DMA/IOMMU mapping path. The invalid allocation result feeds active DMA/IOMMU mapping setup, so this is more security-relevant than a purely local bookkeeping error.
Paranoid additional signal:
* +1 Limited invalid DMA mapping concern. If the invalid page state does not immediately fault, the code may still reach IOMMU mapping logic with an invalid physical page source. This supports manual review, but not a strong corruption primitive.
Non-awarded signals:
* 0 Real UAF. No use-after-free, stale object lifetime, or repeated release/refcount operation is established.
* 0 Concrete repeated release/refcount. No first release, surviving exact dangling reference, or second lifetime mutation is present.
* 0 Controlled reclaim. No attacker-shaped replacement object or post-free reuse is shown.
* 0 Arbitrary or directed write. The patch does not establish attacker control over a write target or payload.
* 0 Confidentiality and integrity. C/I impact is not awarded because no disclosure path, unauthorized write, ownership violation, or controlled corruption primitive is established.
* 0 Remote reachability. The issue is in a DMA allocation helper path, not a packet-processing or network-exposed parser.
* 0 Local unprivileged trigger. A below-host-admin complete trigger path is not established by the supplied patch.
* 0 Extra availability. No second independent availability mechanism is shown beyond the invalid pointer or invalid mapping failure path.
* 0 Race penalty. This is an ordered allocation-failure handling bug, not a timing race.
3. Reachability analysis
The vulnerable path is reached when a device or driver requests a non-blocking, non-coherent DMA allocation through iommu_dma_alloc(), with CONFIG_DMA_DIRECT_REMAP enabled, and dma_alloc_from_pool() fails. The attacker would need to influence a driver or device path that performs this allocation and also create or encounter atomic pool allocation failure conditions.
The complete triggering privilege boundary is not resolved from the patch. It may be reachable through a local device-facing workload, but the exact caller and userspace interface are not visible. Host-admin-equivalent privilege is therefore not positively established, but below-host-admin reachability is also not proven.
Namespace-scoped privilege is not indicated. There is no evidence that an attacker-created namespace can perform the full vulnerable operation.
No direct network reachability is established. No firmware-mediated external trigger is established. No special rare hardware penalty is applied because DMA/IOMMU paths are common enough, but the exact affected runtime path depends on platform and driver behavior.
4. Primitive and severity interpretation
The exact primitive is an unchecked allocation-result mismatch: dma_alloc_from_pool() returns the allocated page and only fills cpu_addr on success, but the old code used cpu_addr as the failure indicator and then used page for page_to_phys() and __iommu_dma_map().
This is not a UAF and not a repeated lifetime/refcount mutation. It is best classified as CLASS_C because the demonstrated behavior is invalid pointer or invalid mapping state leading primarily to crash/DoS, without an independently useful corruption primitive.
The object involved is active DMA/IOMMU mapping state rather than fixed passive metadata, which justifies manual review. However, the patch does not show controlled reclaim, attacker-controlled mapping target selection, arbitrary write, information disclosure, privilege escalation, or a security-boundary bypass.
ImportantCandidate=NO because the evidence supports a borderline/actionable DoS and invalid-state issue, not a strong Important-preserving primitive. AutoDowngradeAllowed=YES because no unresolved Class A or strong Class B primitive remains established.
Likely operational severity is ordinary-to-borderline Moderate, with manual review recommended due to the core DMA/IOMMU mapping context.
5. One-sentence report phrase
An incorrect allocation failure check in the non-blocking non-coherent IOMMU DMA path can allow a NULL or invalid page to be used for DMA mapping, causing a local kernel crash or invalid mapping state under atomic pool allocation failure conditions.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
The bug is not a proven UAF, arbitrary write, or privilege escalation issue, but it affects core DMA/IOMMU mapping logic and may require caller-level review to determine whether any below-host-admin device path can reliably trigger it.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: iommu/dma: Check atomic pool allocation result directly [ Upstream
Commit: ac9cd0a669b8be5d178dbd471b0d68039dac58b5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac9cd0a669b8be5d178dbd471b0d68039dac58b5
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=ac9cd0a669b8be5d178dbd471b0d68039dac58b5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90388 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90388
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: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: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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