[CVE-2026-45919][LOW] sched/rt: Skip currently executing CPU in rto_next_cpu() [ Upstream

[CVE-2026-45919][LOW] sched/rt: Skip currently executing CPU in rto_next_cpu() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45919
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: sched/rt: Skip currently executing CPU in rto_next_cpu() [ Upstream
Commit: d57d0746276a88ea43a2cc62b849fd8a95e32e41
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d57d0746276a88ea43a2cc62b849fd8a95e32e41
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45919
Analysis date: Wed, 27 May 2026 21:26:34 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An RT scheduler load-balancing logic bug can reselect the current overloaded CPU and create repeated self-IPIs, allowing a specialized local RT workload to trigger CPU hardlockup DoS.

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

The original Linux kernel CVE announcement for CVE-2026-45919 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45919

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45919	LOW	CHECK	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-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An RT scheduler load balancing bug can make rto_next_cpu() reselect the currently executing overloaded CPU and queue irq_work to itself. Under a specific multi CPU RT workload this can create a repeated self IPI loop and lead to CPU hardlockup. For the CVSS the PR:L is used in the paranoid score because some deployments delegate RT scheduling through rtprio limits or service policy, although reliable triggering commonly requires CAP_SYS_NICE or privileged control of RT tasks. The issue is not network reachable. Impact is denial of service through CPU hardlockup. No supported evidence indicates information disclosure, integrity impact, kernel memory corruption, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2) 	MAYBE	DEADLOCK WARNONLY HARDWARE 	-	-	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Reliable kernel crash / strong DoS: +1
  The described failure is a CPU hardlockup caused by repeated self-IPIs in RT load balancing.

* Availability impact realistic: +1
  A hardlockup can stall a CPU and may become system-impacting depending on watchdog and workload behavior.

* Broad/default/common subsystem: +1
  The bug is in the core scheduler RT balancing path, although the affected path requires RT workload conditions.

* Local trigger with delegated RT scheduling: +1 in paranoid scoring
  Some systems allow non-root services or users to run RT workloads through `RLIMIT_RTPRIO`, service policy, or delegated scheduling configuration.

* Hard or special workload/timing required: -1
  The scenario requires a multi-CPU RT load-balancing state with one overloaded CPU, other CPUs triggering pull/push behavior, and `HAVE_RT_PUSH_IPI`.

* Requires privileged RT control in typical deployments: -2 conservative
  Reliable setup commonly needs `CAP_SYS_NICE`, root control, or service-level RT scheduling privileges.

* No memory corruption: +0
  The patch shows a scheduler logic bug causing self-IPI looping, not UAF, OOB write, arbitrary write, or object lifetime corruption.

## 3. Reachability analysis

The bug is locally reachable through a specific RT scheduling workload. In ordinary deployments, creating the required RT task mix usually requires `CAP_SYS_NICE` or configured RT priority limits. Namespaces and containers may lower practical privilege requirements if RT scheduling is delegated to containerized workloads or service accounts.

The issue is not network reachable. Realistic exploitation is DoS-only and depends on specialized scheduler conditions rather than a generic unprivileged syscall path.

## 4. Severity interpretation

This behaves like a borderline Moderate availability issue. It is more serious than a simple warning because the impact can be CPU hardlockup, but it is not an Important-class memory corruption or privilege escalation issue. The paranoid score is higher only for environments that delegate RT scheduling to less-privileged users or workloads.

## 5. One-sentence report phrase

An RT scheduler load-balancing logic bug can reselect the current overloaded CPU and create repeated self-IPIs, allowing a specialized local RT workload to trigger CPU hardlockup DoS.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review is recommended only to confirm whether the product delegates RT scheduling to untrusted users or containers. If RT scheduling is restricted to trusted root services, this can be treated as low-priority DoS.

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

Patch: sched/rt: Skip currently executing CPU in rto_next_cpu() [ Upstream
Commit: d57d0746276a88ea43a2cc62b849fd8a95e32e41
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d57d0746276a88ea43a2cc62b849fd8a95e32e41

Changed files:
  kernel/sched/rt.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=d57d0746276a88ea43a2cc62b849fd8a95e32e41

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

The original Linux kernel CVE announcement for CVE-2026-45919 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45919

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: 1
  Paranoid ActionableScore: 3

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).