From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97925][MODERATE REGULAR] tick/broadcast: Plug clockevents replacement race Date: Tue, 29 Sep 2026 15:26:33 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97925 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 List-Id: CVE: CVE-2026-97925 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: tick/broadcast: Plug clockevents replacement race Commit: 3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97925 Analysis date: Tue, 29 Sep 2026 15:26:33 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97925 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97925 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: MODERATE REGULAR 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-2026-97925 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97925 CHECK WITH IMPACT FROM ORIG NN LOW 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-667;CWE-662;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A race in the tick broadcast subsystem can occur when one CPU reads the current broadcast clockevent device while another CPU replaces and detaches that device. The first CPU may then arm the detached device, leaving its state inconsistent with the active broadcast configuration. If the old device has a restricted interrupt affinity mask and the last CPU in that mask goes offline, tick cleanup can reach a BUG condition and cause a kernel crash or system denial of service. For the CVSS the PR:L value in the paranoid score assumes a reduced privilege service, container, or delegated management context that can influence CPU hotplug or the clockevent device lifecycle. Normal system configurations more commonly require PR:H because these operations are controlled by an administrator. The issue is local and is not directly reachable through network traffic. The required timing window makes AC:H appropriate. Impact is limited to availability because the analyzed code provides no concrete UAF dereference, out of bounds access, information leak, or controlled write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE WARNONLY RACE DMAorINTERRUPT HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash / strong DoS. The documented interleaving can arm a detached clockevent device and later trigger BUG during CPU cleanup. * +0 Weak corruption concern. A live pointer is used after the device has been logically detached, but no post-free access, invalid memory write, disclosure, or independently useful corruption primitive is established. * No remote-reachability point. The vulnerable operation is internal clockevent replacement and CPU lifecycle handling, not attacker-controlled network processing. * No local-unprivileged point. The complete trigger is not shown to be reachable by an ordinary user. * No privilege penalty. Host-admin-equivalent control is plausible for CPU hotplug and device management, but it is not positively established for every possible trigger path. * No race penalty. The interleaving is explicit, but the supplied evidence does not establish that it is exceptionally narrow, one-shot, or impractical to reproduce. * No rare-hardware penalty. Restricted interrupt affinity is required for the documented BUG path, but the evidence does not establish genuinely rare physical hardware. * No UAF or repeated-release points. The old device is detached and programmed incorrectly, but the patch does not establish that its storage was freed or that the same reference receives a second lifetime mutation. * No controlled reclaim, arbitrary write, information disclosure, privilege escalation, or security-boundary bypass is demonstrated. * No extra Availability point was awarded because the BUG and resulting crash are the same consequence. 3. Reachability analysis The demonstrated trigger requires a broadcast clockevent replacement racing with a tick broadcast operation. The documented terminal condition additionally requires the old device to have a restricted interrupt affinity mask and the last CPU in that mask to go offline. Direct userspace CPU offlining and clockevent device management are normally privileged operations, but the supplied context does not prove that every device-replacement path requires a host administrator or identify a complete attacker-controlled interface. Therefore HostAdminRequired remains UNKNOWN rather than being inferred as YES or NO. No namespace-scoped capability path is shown. There is no evidence that an attacker-created user or network namespace can perform the complete replacement, broadcast, and CPU-offline sequence. No prior attacker-accessible setup, remote packet trigger, or ordinary unprivileged interface is established. The race is real, but its practical repeatability from a security principal is unresolved. No timing penalty is applied merely because concurrent execution is required. 4. Primitive and severity interpretation The exact primitive is an invalid active-state transition. One CPU retains the old broadcast device pointer while another CPU shuts down and detaches that device. The first CPU can then program the logically detached device, leaving clockevent state inconsistent with later CPU cleanup. The affected clock_event_device is an active structured kernel object, but the supplied evidence shows stale logical state rather than use after free. The module_put split is necessary because the module reference cannot be dropped while holding tick_broadcast_lock. It does not independently prove that the stale path dereferences freed module or device storage. There is no concrete repeated release or refcount mutation. The first operation is a detach and module-reference release associated with replacement, while the documented stale operation arms the detached device rather than performing a second put, free, or refcount decrement. PrimitiveClass is CLASS_C because the established consequence is invalid-state handling followed by BUG and kernel DoS. The theoretical possibility of a deeper lifetime issue is not sufficient to classify this as CLASS_B without evidence of post-lifetime object use. ImportantCandidate is NO because no useful corruption, ownership, authorization, disclosure, or privilege-escalation primitive remains after excluding the crash. AutoDowngradeAllowed is YES because the demonstrated behavior is constrained to crash-capable state inconsistency. Operational severity is ordinary Moderate or Low-like depending on actual device-replacement exposure. 5. One-sentence report phrase A synchronization race can cause the tick broadcast path to arm a detached clockevent device and later trigger a kernel BUG during CPU cleanup, resulting in local denial of service without an established memory-corruption or privilege-escalation primitive. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review the complete clockevent registration and CPU-hotplug call paths to confirm privilege requirements and whether module or device storage can be released while another CPU retains the old pointer, although the supplied patch establishes only invalid-state DoS. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tick/broadcast: Plug clockevents replacement race Commit: 3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 Commit description: 朱恺乾 reported and decoded the following race condition when a broadcast device is replaced: CPUA CPUB __tick_broadcast_oneshot_control() bc = tick_broadcast_device.evtdev; tick_install_broadcast_device(dev) clockevents_exchange_device(cur, dev) shutdown(cur); detach(cur); cur->handler = noop; tick_broadcast_device.evtdev = dev; tick_broadcast_set_event(bc, next_event); <- FAIL: arms a detached device. If the original broadcast device has a restricted interrupt affinity mask and the last CPU in that mask goes offline then the BUG() in tick_cleanup_dead_cpu() triggers because the clockevent device is not in detached state. The reason for this is that tick_install_broadcast_device() is not serialized vs. tick broadcast operations. The obvious cure is to serialize tick_install_broadcast_device() with tick_broadcast_lock against a concurrent tick broadcast operation. That requires to split clockevents_exchange_device() into two parts, one which does the exchange, shutdown and detach operation and the other which drops the module reference count. This is required because the module reference cannot be dropped while holding tick_broadcast_lock. Let clockevents_exchange_device() do both operations as before, but let the broadcast device code take the two step approach and do the device exchange under tick_broadcast_lock and drop the module reference count after releasing it. Fixes: f8381cb ("[PATCH] tick-management: broadcast functionality") Reported-by: 朱恺乾 Signed-off-by: Thomas Gleixner Signed-off-by: Thomas Gleixner Reviewed-by: Bradley Morgan Tested-by: 刘术高 Cc: stable@vger.kernel.org Link: https://patch.msgid.link/87cymdsu0r.ffs@tglx Signed-off-by: Greg Kroah-Hartman Changed files: kernel/time/clockevents.c kernel/time/tick-broadcast.c kernel/time/tick-internal.h 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=3da55616db2b6b7d9caa3b7ff1e8983224e0ed52 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97925 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97925 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: unknown 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: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).