[CVE-2026-53326][LOW] debugobjects: Dont call fill_pool() in early boot hardirq context

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

CVE: CVE-2026-53326
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: debugobjects: Dont call fill_pool() in early boot hardirq context
Commit: 44b8b03a9fb5c575548fc72c674653d6baba142a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44b8b03a9fb5c575548fc72c674653d6baba142a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53326
Analysis date: Wed, 01 Jul 2026 10:16:39 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A debugobjects pool refill can occur from early boot hardirq context on PREEMPT_RT before scheduling is active, creating a lock inversion that may deadlock the system during boot, but it requires a non-default debug RT kernel environment and does not expose memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53326 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53326

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53326	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'debugobjects pool refill may run from early boot hardirq context on PREEMPT_RT before the scheduler is active. In that window an interrupt handler can enter debug_objects_fill_pool while the interrupted code holds a lock that is also needed by the allocation path, causing lock inversion and a possible deadlock or boot-time denial of service. For the CVSS the PR:H is used because reliable triggering depends on a debug PREEMPT_RT boot environment and administrator level control over the kernel configuration or boot path. The issue is not network reachable and is not triggered by normal packet or syscall traffic after boot. Impact is availability only, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-53326  SKIP The Fixes patch not applied yet, so unlikely that actual: 06e0ae988f6e3499785c407429953ade19c1096b YES  NO NO unknown 	MAYBE	LOCK DEADLOCK WARNONLY DMAorINTERRUPT LINUS BOOT 	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

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

## 2. Signal breakdown

Positive signals:

* Reliable kernel crash / strong DoS: **+1 paranoid only**
  The commit describes a possible lock inversion leading to deadlock during early boot on PREEMPT_RT.

Negative signals:

* Requires admin/root/kernel configuration control in typical deployments: **-2**
  Reliable exposure depends on booting a debug PREEMPT_RT kernel and controlling the kernel or boot environment.

* Legacy / non-default execution mode: **-1**
  The issue requires CONFIG_PREEMPT_RT and debugobjects behavior during a narrow early boot window.

* Rare and difficult-to-reach configuration: **-1**
  The affected path is early boot before SYSTEM_SCHEDULING, not a normal runtime syscall, network, filesystem, or device data path.

* Hard or unreliable timing condition: **-1**
  The problematic interrupt must occur while the interrupted code holds a lock also needed by the allocation path.

Not applied:

* No remote/network reachability.
* No local unprivileged trigger.
* No UAF, double-free, OOB write, type confusion, refcount abuse, or stale callback.
* No confidentiality or integrity impact.
* No privilege escalation plausibility.

## 3. Reachability analysis

The bug is reachable only in a very specific boot-time condition on PREEMPT_RT debug kernels. It requires interrupts to fire before the scheduler is active and for the interrupt handler to enter debug_objects_fill_pool while the interrupted context holds a conflicting lock.

Namespaces and containers do not meaningfully reduce the privilege requirement because the issue is not exposed through a normal userspace API after boot. An attacker would generally need administrative control over the kernel configuration, boot process, or hardware/interrupt environment. The path is not default-enabled for ordinary production kernels.

## 4. Severity interpretation

This behaves like a **Low-like / ordinary Moderate reliability issue**, not an Important-class vulnerability. The realistic impact is boot-time deadlock or lockdep warning on a debug PREEMPT_RT system.

Theoretical impact is availability-only. There is no evidence in the patch of memory corruption, attacker-controlled object reuse, information disclosure, privilege escalation, or a practical runtime attack surface.

## 5. One-sentence report phrase

A debugobjects pool refill can occur from early boot hardirq context on PREEMPT_RT before scheduling is active, creating a lock inversion that may deadlock the system during boot, but it requires a non-default debug RT kernel environment and does not expose memory corruption or privilege escalation.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

This can be auto-closed for security triage unless the product specifically ships debug PREEMPT_RT kernels and treats boot-time deadlocks as security-impacting availability issues.

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

Patch: debugobjects: Dont call fill_pool() in early boot hardirq context
Commit: 44b8b03a9fb5c575548fc72c674653d6baba142a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44b8b03a9fb5c575548fc72c674653d6baba142a

Commit description:

When booting a debug PREEMPT_RT kernel on an ARM64 system, a "inconsistent
{HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage" lockdep warning message was
reported to the console.

During early boot, interrupts are enabled before the scheduler is
enabled. In this window (before SYSTEM_SCHEDULING is set) interrupts can
fire and in the hard interrupt context handler attempt to fill the pool

This can lead to a deadlock when the interrupt occurred when the interrupt
hits a region which holds a lock that is required to be taken in the
allocation path.

Add a new can_fill_pool() helper and reorder the exception rule and forbid
this scenario by excluding allocations from hard interrupt context.

Fixes: 06e0ae9 ("debugobjects: Allow to refill the pool before SYSTEM_SCHEDULING")
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260605173038.495075-1-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  lib/debugobjects.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=44b8b03a9fb5c575548fc72c674653d6baba142a

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

The original Linux kernel CVE announcement for CVE-2026-53326 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53326

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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: 0
  Paranoid ActionableScore: 1

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).