[CVE-2026-90387][LOW] swiotlb: Preserve allocation virtual address for dynamic pools [ Upstream

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

CVE: CVE-2026-90387
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: swiotlb: Preserve allocation virtual address for dynamic pools [ Upstream
Commit: 68bf3ebd8e7020dae58e8aa14c7d482738bff9a8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68bf3ebd8e7020dae58e8aa14c7d482738bff9a8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90387
Analysis date: Fri, 18 Sep 2026 07:52:14 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90387 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90387

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-2026-90387	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90387 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:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A SWIOTLB dynamic pool backed by the DMA atomic pool can store the wrong virtual address when CONFIG_DMA_DIRECT_REMAP is used. The allocation path may return a remapped virtual address, but the pool initialization rebuilt the address with phys_to_virt and later passed that mismatched address to dma_free_from_pool. This can prevent the pool allocator from recognizing the chunk during free and can leak DMA atomic pool resources over repeated allocation and free cycles. For the CVSS the PR:L is used because a local user or local workload may be able to drive device I/O paths that allocate transient SWIOTLB pools, but reliable triggering still depends on specific DMA, encryption, atomic context, and pool pressure conditions. The issue is not directly network reachable as a protocol bug. Impact is denial of service through resource exhaustion, with no supported evidence of memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	OOB LOCK INIT DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Conservative positive signals:

* +1 Concrete persistent kernel resource/reference leak: the patch establishes that a SWIOTLB dynamic pool allocation can store the wrong virtual address and later fail to be recognized by `dma_free_from_pool()`, causing the allocation to remain unreleased through the normal free path.

Paranoid additional signals:

* +1 Resource exhaustion concern: repeated allocation/free cycles under the affected configuration could plausibly exhaust DMA atomic pool resources or related memory, causing availability impact. This is counted only in the paranoid score because the patch does not show immediate host-wide failure from one operation.

Negative or non-awarded signals:

* +0 Real UAF not awarded: no use-after-free, stale object dereference, double free, or repeated lifetime/refcount mutation is established.
* +0 Memory corruption not awarded: the bug is a wrong virtual address used for pool accounting/free recognition, not an OOB write, arbitrary write, controlled overwrite, or object replacement.
* +0 Reliable kernel crash not awarded: the commit supports a leak/free-path mismatch, not an immediate panic or deterministic crash.
* +0 Remote reachability not awarded: no network protocol path directly reaches the vulnerable operation.
* +0 Local unprivileged trigger not awarded: a local workload may influence device I/O, but the complete below-host-admin trigger chain is not positively established.
* +0 C/I impact not awarded: no disclosure, protected state modification, privilege escalation, or security-boundary bypass is supported.
* -0 Host-admin penalty not applied: host-admin-equivalent privilege is not positively established.
* -0 Rare configuration penalty not applied in arithmetic: the affected path depends on CONFIG_DMA_DIRECT_REMAP, DMA atomic pool use, forced unencrypted DMA, atomic context, and transient SWIOTLB pool allocation, but these conditions are treated as reachability limitations rather than an extra numeric penalty to avoid unsupported restrictive-deployment scoring.

3. Reachability analysis

The affected path is in `kernel/dma/swiotlb.c` and is reached when SWIOTLB allocates dynamic pools. The problematic case is specifically an allocation from the DMA atomic pool when a decrypted pool is needed from atomic context and CONFIG_DMA_DIRECT_REMAP causes the returned virtual address to differ from the direct-map address.

A normal local user or workload may indirectly drive DMA activity through devices, but the supplied evidence does not prove that an ordinary user can reliably force the exact atomic SWIOTLB dynamic-pool allocation and free cycle. Host-admin-equivalent privilege is also not positively established as required for the complete trigger. Therefore HostAdminRequired is UNKNOWN.

No namespace-scoped privilege path is shown. There is no evidence that a user namespace or network namespace provides the complete ability to instantiate and trigger this SWIOTLB path. NamespaceScopedPrivilege is NO.

There is no direct network reachability. Any network-related triggering would be indirect through device I/O and DMA behavior, not a protocol parser bug. The issue depends on kernel configuration and platform/device DMA behavior, but no rare physical-only hardware requirement is established from the patch.

4. Primitive and severity interpretation

The exact primitive is a concrete resource/free-path mismatch: `swiotlb_init_io_tlb_pool()` previously reconstructed `pool->vaddr` with `phys_to_virt(start)`, but for DMA atomic pool allocations under CONFIG_DMA_DIRECT_REMAP the allocation path may return a remapped virtual address. Later `swiotlb_free_tlb()` passes the stored address to `dma_free_from_pool()`, which may fail to recognize the chunk.

This is not an active structured UAF and not fixed stale storage with post-free access. It is a persistent resource leak / resource accounting failure. There is no concrete repeated release/refcount operation, because the bug is failure to release a chunk rather than a second lifetime mutation through a dangling reference.

PrimitiveClass is NONE because no kernel corruption, UAF, ownership violation, authorization bypass, or semantic security-boundary primitive is established. The demonstrated consequence is resource leakage. The speculative consequence is availability degradation if repeated activity accumulates enough leaked pool memory. There is no supported path to privilege escalation, information disclosure, or integrity compromise.

ImportantCandidate is NO because the issue is resource exhaustion only and lacks memory corruption, boundary bypass, or unresolved exploitation leverage. AutoDowngradeAllowed is YES because no meaningful kernel-corruption or security-boundary primitive would be lost by treating it as ordinary Moderate/Low-like.

5. One-sentence report phrase

A SWIOTLB dynamic pool backed by the DMA atomic pool can store a mismatched virtual address under CONFIG_DMA_DIRECT_REMAP, preventing dma_free_from_pool from recognizing the chunk and causing a configuration dependent resource leak that may lead to DoS only after repeated pressure.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a concrete but constrained resource leak without UAF, memory corruption, remote reachability, authorization bypass, or privilege-escalation evidence.

7. Call-site confidence

Call-site confidence: high

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

Patch: swiotlb: Preserve allocation virtual address for dynamic pools [ Upstream
Commit: 68bf3ebd8e7020dae58e8aa14c7d482738bff9a8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68bf3ebd8e7020dae58e8aa14c7d482738bff9a8

Changed files:
  kernel/dma/swiotlb.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=68bf3ebd8e7020dae58e8aa14c7d482738bff9a8

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

The original Linux kernel CVE announcement for CVE-2026-90387 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90387

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  Paranoid ActionableScore: 2

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).