* [CVE-2026-90429][MODERATE 7.0] iommu/tegra241-cmdqv: Synchronize the error ISR against VINTF (de)init [ Upstream
@ 2026-09-18 2:30 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 2:30 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90429
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: iommu/tegra241-cmdqv: Synchronize the error ISR against VINTF (de)init [ Upstream
Commit: bcb82407633c3008362ad927699d985ee4981557
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcb82407633c3008362ad927699d985ee4981557
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90429
Analysis date: Thu, 17 Sep 2026 22:30:53 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race in the Tegra241 CMDQV IOMMU VINTF lifecycle can let the error ISR dereference a NULL, partially initialized, or post-lifetime VINTF, causing at least a local kernel crash and requiring manual review for possible UAF exploitation beyond DoS.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90429 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90429
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90429 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90429 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-362;*CWE-416;**CWE-476;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the Tegra241 CMDQV IOMMU driver can let the error interrupt handler observe a VINTF slot while it is being created or torn down. This can produce a NULL pointer dereference or a use-after-free when the ISR dereferences a VINTF that is NULL, partially initialized, or about to be freed. For the CVSS the PR:L is chosen because reliable triggering requires a local process with access to iommufd or delegated device assignment that can create or destroy user VINTFs. AC:H is used because the bug depends on a timing window between interrupt handling and VINTF lifecycle operations. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the patch context explicitly describes a use-after-free candidate in an interrupt path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES INIT UAF DMAorINTERRUPT HARDWARE LINUS KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
## 1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4
* Applied conservative floor/cap: Real UAF floor 4 applied, 3 -> 4
* Raw paranoid score: 5
* Paranoid score: 5
* Applied paranoid floor/cap: none
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
## 2. Signal breakdown
Conservative signals:
* +2 Real UAF / active lifetime violation: the ISR can read `cmdqv->vintfs[idx]` while `tegra241_cmdqv_deinit_vintf()` is tearing down the VINTF, allowing NULL dereference or use of a VINTF that is about to be freed.
* +1 Reliable kernel crash / strong DoS: the patch text explicitly describes NULL dereference and UAF in interrupt handling, both realistic kernel crash paths.
* +1 Active ISR synchronization / lifetime invariant failure: teardown did not drain the error IRQ before the VINTF could be freed or its ID reused.
* -1 Hard timing / interrupt race: exploitation depends on a concurrent error interrupt racing with VINTF init or deinit.
Conservative raw total: 2 + 1 + 1 - 1 = 3.
Conservative floor: Real UAF floor 4 applies because a real stale object can be dereferenced and host-admin-equivalent privilege is not positively established.
Paranoid additional signals:
* +1 Attacker-influenced active-object lifetime / reuse concern: user VINTF create and destroy paths, IDA index reuse, and slot publication are directly involved, so repeated lifecycle manipulation is plausible if the attacker has access to the user VINTF interface.
* +1 Structured stale-object exploitation leverage: the stale or prematurely published VINTF is not just passive storage. The ISR can consume structured fields such as `vintf->base` and pass the object into VINTF error handlers.
Paranoid raw total: 2 + 1 + 1 + 1 + 1 - 1 = 5.
Important non-awarded signals:
* Controlled reclaim is not demonstrated.
* Arbitrary read/write is not demonstrated.
* Callback or function-pointer control is not demonstrated.
* Remote network reachability is not established.
* Confidentiality and integrity impact are not awarded as direct signals.
* Concrete repeated release/refcount mutation is not established.
* Extra availability is not awarded because the crash is already counted.
* Hardware specificity is noted, but no hardware penalty is applied because the affected driver path is the evaluated vulnerable configuration.
Repeated release/refcount check:
* First release can end lifetime: possibly, through VINTF teardown and later iommufd freeing.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* Floor 5 based on repeated release/refcount: not applied.
## 3. Reachability analysis
The reachable object is a user VINTF in the Tegra241 CMDQV IOMMU driver. The relevant operations are VINTF creation, VINTF teardown, init-failure unwind, and an asynchronous CMDQV error interrupt.
The complete attacker privilege boundary is not fully resolved from the supplied patch. The text says this is user-space use support and refers to iommufd core, so a local userspace component with access to the relevant IOMMU/device-assignment interface is plausibly involved. However, the supplied evidence does not prove that an ordinary unprivileged user can complete the full trigger chain without prior device assignment or administrative setup. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.
Namespace-scoped privilege is also UNKNOWN. No evidence shows that all required VINTF creation, teardown, device assignment, and interrupt-triggering stages are fully available inside attacker-created namespaces.
Prior host setup may exist in practice if the platform requires device assignment or exposure of the iommufd-controlled object to a user process. The vulnerable hardware is Tegra241 CMDQV, so the issue is hardware/platform-specific. The race is interrupt/lifecycle dependent and likely timing-sensitive, but repeated create/destroy attempts may be possible for an actor that controls the user VINTF lifecycle.
## 4. Primitive and severity interpretation
The exact primitive is a race between ISR dereference and VINTF lifecycle changes. The ISR can observe a NULL slot, a partially initialized VINTF, or a VINTF that is being torn down and may be freed. This establishes a real active structured-object UAF candidate, not merely a passive bookkeeping issue.
The stale storage is an active structured object rather than a fixed DMA buffer. The ISR may pass the object into error handlers and dereference fields such as `vintf->base`. The bug is not limited to a simple cleanup-only stale dereference because the stale use happens in an asynchronous interrupt handler during normal error processing.
No concrete repeated release/refcount operation is established. The stronger concern is ISR consumption of a stale or not-fully-published structured object, plus missing `synchronize_irq()` before ID reuse and eventual free.
PrimitiveClass is CLASS_B. This is a real kernel lifetime/synchronization primitive with unresolved exploitation leverage, but the supplied evidence does not establish CLASS_A capabilities such as controlled reclaim, arbitrary kernel write, refcount takeover, callback control, or demonstrated privilege escalation.
The demonstrated consequence is local kernel crash / DoS. The speculative consequence is possible exploitation beyond DoS due to UAF in an interrupt path, but that requires manual review of allocator behavior, object reuse, attacker control over VINTF lifecycle, and what the error handlers consume.
ImportantCandidate is YES because this is an active structured UAF in an IOMMU driver with user-space VINTF support and unresolved post-lifetime behavior. AutoDowngradeAllowed is NO because automatically closing this as ordinary crash-only would lose a concrete UAF/lifecycle primitive that still needs Important-vs-Moderate review.
Likely operational severity is Actionable Moderate, with Strong Important candidacy depending on whether below-host-admin reachability and useful post-free object reuse can be confirmed.
## 5. One-sentence report phrase
A race in the Tegra241 CMDQV IOMMU VINTF lifecycle can let the error ISR dereference a NULL, partially initialized, or post-lifetime VINTF, causing at least a local kernel crash and requiring manual review for possible UAF exploitation beyond DoS.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch directly establishes a real UAF candidate in an interrupt handler and a missing synchronization barrier before object free and ID reuse. Controlled reclaim or LPE is not shown, but the active structured stale-object behavior is strong enough that automatic downgrade is unsafe.
## 7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: iommu/tegra241-cmdqv: Synchronize the error ISR against VINTF (de)init [ Upstream
Commit: bcb82407633c3008362ad927699d985ee4981557
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcb82407633c3008362ad927699d985ee4981557
Changed files:
drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.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=bcb82407633c3008362ad927699d985ee4981557
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90429 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90429
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: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: YES
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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