From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98418][LOW] sched/core: Avoid false migration warning for proxy donors [ Upstream Date: Wed, 14 Oct 2026 22:49:46 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98418 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: e4a442da49fff7619b3cb2988e477022dcea6688 List-Id: CVE: CVE-2026-98418 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: sched/core: Avoid false migration warning for proxy donors [ Upstream Commit: e4a442da49fff7619b3cb2988e477022dcea6688 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4a442da49fff7619b3cb2988e477022dcea6688 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98418 Analysis date: Wed, 14 Oct 2026 22:49:46 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A valid proxy-donor scheduling-context migration can trigger a false migration-disabled warning, but no crash, memory corruption, authorization bypass, or confidentiality, integrity, or availability impact is established. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98418 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98418 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-2026-98418 LOW https://www.kernelcve.org/list/?q=CVE-2026-98418 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both LOW) 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:N';CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '0';DESCR 'A blocked proxy donor can have its scheduling context moved to the lock owner CPU while its migration disabled execution context remains associated with the original CPU. set_task_cpu can misinterpret this valid transient state and emit a migration warning even though the donor does not execute on the temporary CPU and the wakeup path returns it to an executable placement. For the CVSS the PR:L is used in the paranoid interpretation because a local process may indirectly exercise proxy locking paths on a kernel with proxy execution enabled, although reliable reproduction may require a specialized workload or test module. The demonstrated effect is a false kernel warning only. There is no supported UAF, invalid memory access, information disclosure, privilege escalation, kernel crash, or availability loss. The issue is not network reachable and has no confidentiality, integrity, or availability impact. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 0 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE LOCK WARNONLY HARDWARE - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO ## 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 0 * Paranoid score: 0 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: ## 2. Signal breakdown * **+0 False WARN_ON:** `set_task_cpu()` incorrectly warns for a valid proxy-donor migration state. `WARN_ON_ONCE` continues execution, and the reproducer completes normally. * **+0 Corruption primitive:** no UAF, OOB access, stale lifetime operation, invalid write, refcount mutation, or active-state retirement bypass is established. * **+0 Availability:** no panic, lockup, persistent resource consumption, or operational failure is demonstrated. * **+0 Authorization:** the changed condition is a diagnostic assertion, not an access-control decision. There is no DENY-to-ALLOW transition. * **+0 Reachability:** local triggering may be possible, but it creates no security impact and therefore earns no reachability bonus. * **No negative signals applied:** privilege and timing uncertainty are not used as unsupported penalties. * Controlled reclaim, arbitrary write, confidentiality impact, integrity impact, privilege escalation, remote reachability, and protected-resource access are not demonstrated. * NEW52 B5-R does not apply because there is no OOB write or retry-accumulated corruption. * NEW53 B3-PENDING does not apply because there is no shared-backing write. * NEW54 B4-PENDING does not apply because no authorization decision is changed. Arithmetic: `0 = 0`. ## 3. Reachability analysis The demonstrated reproducer creates a mutex owner on one CPU and a migration-disabled blocked donor on another CPU under proxy execution. The supplied evidence does not establish whether an ordinary process can independently construct the complete state or whether a test module or specialized kernel workload is required. Therefore, effective host-admin requirements remain unknown rather than being assumed either way. No namespace capability, prior privileged configuration, special hardware, remote interface, or attacker-controlled race is established. Proxy execution support is a configuration prerequisite. The behavior is a valid scheduling transition whose only faulty consequence is a diagnostic warning. ## 4. Primitive and severity interpretation The exact defect is an overly broad diagnostic condition in `set_task_cpu()`. A blocked proxy donor may have its scheduling context temporarily represented on the lock owners CPU while its migration-disabled execution context remains associated with `wake_cpu`. The wakeup path restores executable placement before clearing the blocked state. There is no stale object, post-lifetime access, repeated release, memory corruption, authorization bypass, or security-boundary primitive. The demonstrated consequence is a false one-time warning followed by successful completion. Consequently, the classification is `NONE`, `ImportantCandidate=NO`, and automatic downgrade is safe. Operational severity is informational or non-security correctness impact. ## 5. One-sentence report phrase A valid proxy-donor scheduling-context migration can trigger a false migration-disabled warning, but no crash, memory corruption, authorization bypass, or confidentiality, integrity, or availability impact is established. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch only refines a diagnostic assertion for a valid scheduler state and establishes no security-relevant primitive or consequence. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sched/core: Avoid false migration warning for proxy donors [ Upstream Commit: e4a442da49fff7619b3cb2988e477022dcea6688 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4a442da49fff7619b3cb2988e477022dcea6688 Changed files: kernel/sched/core.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=e4a442da49fff7619b3cb2988e477022dcea6688 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98418 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98418 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:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:N The Best / paranoid CVSS score: 0 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: 0 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).