[CVE-2026-90397][MODERATE REGULAR] firmware: qcom: scm: Fix NULL dereference in IRQ handler before __scm is published [ Upstream

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

CVE: CVE-2026-90397
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: firmware: qcom: scm: Fix NULL dereference in IRQ handler before __scm is published [ Upstream
Commit: b451f38cb7f5bca78484362347f039c08c94de95
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b451f38cb7f5bca78484362347f039c08c94de95
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90397
Analysis date: Fri, 18 Sep 2026 07:55:52 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A NULL pointer dereference in Qualcomm SCM wait queue handling can occur during qcom_scm_probe when IRQ or non atomic SMC WAITQ paths dereference `__scm` before publication, causing a local platform DoS without evidence of UAF, privilege escalation, or remote reachability.

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

The original Linux kernel CVE announcement for CVE-2026-90397 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90397

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: 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-2026-90397	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90397 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:N/I:N/A:H';**CWE-476;CWE-362;CWE-665;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference can occur in the Qualcomm SCM wait queue handling path because the IRQ handler and non atomic SMC wait path can dereference the global `__scm` pointer before it is published during qcom_scm_probe. An interrupt or WAITQ_SLEEP response during this initialization window can make qcom_scm_get_completion access an uninitialized global pointer and crash the kernel. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate device bind or driver control to a reduced capability local service or container root, although normal systems usually require administrator privileges for reliable triggering. The issue is not network reachable and is tied to local platform initialization or driver control paths on Qualcomm hardware. Impact is denial of service via kernel crash, with no supported evidence of confidentiality impact, integrity impact, UAF, OOB write, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	NULLPTR SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap changed the score.
* Final recommended bucket: **Ordinary Moderate**::

## 2. Signal breakdown

Positive signals:

* +1 Weak indirect corruption or invalid-state primitive. The vulnerable paths dereference the global `__scm` pointer before it is published, producing a NULL pointer dereference rather than a UAF or controlled corruption.
* +1 Reliable kernel crash / strong DoS. The commit directly says both paths can cause NULL pointer dereference, which is a realistic kernel crash or boot/probe failure.
* +1 Firmware-mediated platform trigger surface. The issue depends on Qualcomm SCM IRQ or non-atomic SMC WAITQ_SLEEP behavior during probe, so firmware or platform timing is material.

Negative signals:

* -1 Narrow initialization timing. The bug is limited to the window before `smp_store_release(&__scm, scm)` during `qcom_scm_probe`, including IRQ or WAITQ_SLEEP arrival before publication.

Important non-awarded signals:

* UAF not awarded. The patch shows NULL dereference of an unpublished global pointer, not post-free object use.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded.
* Privilege escalation not awarded.
* Remote reachability not established.
* Extra availability point not awarded because the crash/probe failure is already counted.
* Concrete repeated release/refcount signal not awarded. There is no first put/free followed by a second lifetime mutation on the same dangling reference.
* Structured stale-object leverage not awarded because there is no stale active object reuse.
* Strong LPE or strong exploitation leverage not awarded.

## 3. Reachability analysis

The vulnerable operation occurs during Qualcomm SCM driver probe and wait-queue handling. One path is an IRQ handler that receives `scm` as handler data but previously called helpers that dereferenced the global `__scm`. The second path is a non-atomic SMC call during probe that can return WAITQ_SLEEP before `__scm` is published.

A normal local user trigger is not established. Reliable deliberate triggering likely requires control over driver probing, binding, reboot timing, platform firmware behavior, or device management, but the supplied evidence does not fully prove a host-admin-only attacker model for every affected deployment. Therefore `HostAdminRequired=UNKNOWN` rather than YES or NO.

The issue is not namespace scoped. There is no evidence that user namespaces, network namespaces, or container-scoped capabilities can complete the trigger chain.

There is no network trigger. The input is firmware/platform mediated, not attacker-supplied remote traffic. Special Qualcomm hardware or firmware support is required, but this is not treated as rare physical-only hardware in the scoring because the affected platform context itself is Qualcomm SCM.

Race repeatability is limited by the probe-time publication window and firmware IRQ or WAITQ ordering, so a timing penalty is justified.

## 4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference of `__scm` before publication. This is an initialization ordering and race-style bug, not a real UAF, not a double free, and not a refcount/lifetime mutation.

The affected object is an active driver context, but the stale-use model does not apply because the pointer is not freed and reused. The demonstrated consequence is kernel crash, probe failure, or platform DoS during SCM initialization.

Speculative consequences beyond DoS are not supported by the patch. There is no evidence of attacker-controlled replacement data, arbitrary read/write, callback control, credential corruption, or security-boundary bypass.

PrimitiveClass is CLASS_C because the demonstrated behavior is crash/invalid-state behavior without an independently useful corruption primitive.

ImportantCandidate is NO because no Class A primitive and no strong Class B lifetime/corruption primitive is established. ManualReview is RECOMMENDED because this is a firmware IRQ/probe ordering bug where platform-specific behavior can affect operational impact. AutoDowngradeAllowed is YES because the established issue is constrained DoS with no unresolved UAF, refcount, ownership, authorization, or memory-corruption leverage.

Likely operational severity is ordinary Moderate or Low-like for security triage, with practical concern mainly for affected Qualcomm platforms during initialization or driver reprobe.

## 5. One-sentence report phrase

A NULL pointer dereference in Qualcomm SCM wait queue handling can occur during qcom_scm_probe when IRQ or non atomic SMC WAITQ paths dereference `__scm` before publication, causing a local platform DoS without evidence of UAF, privilege escalation, or remote reachability.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Recommended because the issue is platform and firmware timing dependent, but current evidence supports DoS only and does not establish memory corruption or a security-boundary bypass.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: firmware: qcom: scm: Fix NULL dereference in IRQ handler before __scm is published [ Upstream
Commit: b451f38cb7f5bca78484362347f039c08c94de95
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b451f38cb7f5bca78484362347f039c08c94de95

Changed files:
  drivers/firmware/qcom/qcom_scm-smc.c
  drivers/firmware/qcom/qcom_scm.c
  drivers/firmware/qcom/qcom_scm.h

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=b451f38cb7f5bca78484362347f039c08c94de95

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

The original Linux kernel CVE announcement for CVE-2026-90397 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90397

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:H
  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: unknown
  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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).