[CVE-2026-68090][LOW] debugobjects: Plug race against a concurrent OOM disable

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

CVE: CVE-2026-68090
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: debugobjects: Plug race against a concurrent OOM disable
Commit: 2d5e320b7ab9b25229ac4331541964a58b5e1d29
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d5e320b7ab9b25229ac4331541964a58b5e1d29
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68090
Analysis date: Mon, 10 Aug 2026 11:40:31 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local race in debugobjects during concurrent OOM disable can allow a debug fixup to run after debug objects are disabled, potentially making an hrtimer dysfunctional and causing WARN or denial of service behavior on debug enabled kernels.

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

The original Linux kernel CVE announcement for CVE-2026-68090 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68090

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-2026-68090	LOW	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-362;CWE-703;CWE-754;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 race in debugobjects can occur when debug_object_assert_init() or debug_object_activate() runs while a concurrent OOM path disables debug objects and frees the related shadow objects. In that state the normal debug warning may be skipped, but the fixup callback can still run and may turn a valid object into a dysfunctional one. For hrtimers this can install stub_timer() and later trigger a WARN in the timer path. For the CVSS the PR:L is used because triggering requires local code execution or a local process able to create relevant kernel objects and drive memory pressure, but it does not normally require full administrator privileges. The issue is not network reachable. Impact is mainly denial of service or functional breakage in debug enabled kernels, with no supported evidence for confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	INIT RACE UAF TIMER LINUS SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process can plausibly create timer-related kernel objects and contribute to memory pressure, although reliable triggering requires a specific OOM race.
* Availability impact realistic: +1. The bug can make a valid hrtimer dysfunctional and later trigger a WARN in the timer path.
* Hard or unreliable race / special timing required: -1. The condition requires concurrent debug object lookup and OOM-driven disabling/freeing of debugobjects state.
* Rare AND difficult-to-reach subsystem/configuration: -1. This depends on CONFIG_DEBUG_OBJECTS / debugobjects being enabled, which is commonly a debug or diagnostic configuration rather than a default production setting.
* Reliable kernel crash / strong DoS: +1 only in paranoid scoring. The demonstrated symptom is a WARN and broken timer behavior, not a guaranteed panic unless panic_on_warn or similar policy is active.
* Generic memory corruption: +0. The patch does not show UAF reuse, stale object dereference after free, OOB access, arbitrary write, refcount takeover, or callback control by an attacker.
* Privilege escalation plausible: +0. No reclaim, overwrite, type confusion, controlled callback dispatch, or practical LPE primitive is supported by the patch.

## 3. Reachability analysis

The likely trigger is local. A local user or workload would need to create relevant debug-tracked objects and concurrently drive memory pressure so that debugobjects is disabled while debug_object_assert_init() or debug_object_activate() proceeds toward print or fixup handling. No network reachability is indicated. Namespaces do not materially improve reachability beyond ordinary local execution, because the key condition is kernel-wide OOM/debugobjects state rather than a namespace-specific API. The path is only relevant when debugobjects support is enabled, reducing practical exposure on production kernels.

Call-site confidence: high. The commit explicitly identifies debug_object_assert_init(), debug_object_activate(), hrtimer_fixup_assert_init(), and the resulting stub_timer WARN path.

## 4. Severity interpretation

This behaves like ordinary Moderate or Low-like operational DoS rather than an Important-class vulnerability. The theoretical impact is timer dysfunction and warning/crash behavior in debug-enabled kernels under a narrow race with OOM. Realistic exploitation evidence does not support confidentiality impact, integrity impact, privilege escalation, or strong memory corruption.

## 5. One-sentence report phrase

A local race in debugobjects during concurrent OOM disable can allow a debug fixup to run after debug objects are disabled, potentially making an hrtimer dysfunctional and causing WARN or denial of service behavior on debug enabled kernels.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is race-dependent, debug-configuration-dependent, and does not show a concrete memory corruption or privilege escalation primitive.

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

Patch: debugobjects: Plug race against a concurrent OOM disable
Commit: 2d5e320b7ab9b25229ac4331541964a58b5e1d29
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d5e320b7ab9b25229ac4331541964a58b5e1d29

Commit description:

syzbot reported a puzzling splat:

   WARNING: kernel/time/hrtimer.c:443 at stub_timer+0xa/0x20

stub_timer() is installed as timer callback function in
hrtimer_fixup_assert_init(), which is invoked when
debug_object_assert_init() can't find a shadow object. In that case debug
objects emits a warning about it before invoking the fixup.

Though the provided console log lacks this warning and instead has the
following a few seconds before the splat:

     ODEBUG: Out of memory. ODEBUG disabled

So the object was looked up in debug_object_assert_init() and the lookup
failed due a concurrent out of memory situation which disabled debug
objects and freed the shadow objects:

debug_object_assert_init()
        if (!debug_objects_enabled)
        	return;                         obj = alloc();
                				if (!obj) {
							// Out of memory
                                                	debug_objects_enabled = false;
                                                        free_objects();
        obj = lookup_or_alloc();

        // The lookup failed because the other side
        // removed the objects, so this returns
        // an error code as the object in question
        // is not statically initialized

	if (!IS_ERR_OR_NULL(obj))
        	return;
        if (!obj) {
        	debug_oom();
                return;
        }

        print(...)
           if (!debug_objects_enabled)
                return;

        fixup(...)

The debug object splat is skipped because debug_objects_enabled is false,
but the fixup callback is invoked unconditionally, which makes the timer
disfunctional.

This is only a problem in debug_object_assert_init() and
debug_object_activate() as both have to handle statically initialized
objects and therefore must handle the error pointer return case
gracefully. All other places only handle the found/not found case and the
NULL pointer return is a signal for OOM. Otherwise they get a valid shadow
object.

Plug the hole by checking whether debug objects are still enabled before
invoking the print and fixup function in those two places.

Fixes: b84d435 ("debugobjects: Extend to assert that an object is initialized")
Reported-by: syzbot+5e8dda76ca21dae314b6@syzkaller.appspotmail.com
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/874iiwlzlb.ffs@fw13
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/time/hrtimer.c
  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=2d5e320b7ab9b25229ac4331541964a58b5e1d29

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

The original Linux kernel CVE announcement for CVE-2026-68090 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68090

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).