From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45919][LOW] sched/rt: Skip currently executing CPU in rto_next_cpu() [ Upstream Date: Wed, 27 May 2026 21:26:34 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45919 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: d57d0746276a88ea43a2cc62b849fd8a95e32e41 List-Id: 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).