From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89753][LOW] mm/vmscan: report RCU-tasks quiescent states in shrink_lruvec() Date: Fri, 11 Sep 2026 23:26:06 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89753 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: b5391676c61d94ffe3272dcf6723738b802f79e8 List-Id: CVE: CVE-2026-89753 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: mm/vmscan: report RCU-tasks quiescent states in shrink_lruvec() Commit: b5391676c61d94ffe3272dcf6723738b802f79e8 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5391676c61d94ffe3272dcf6723738b802f79e8 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89753 Analysis date: Fri, 11 Sep 2026 23:26:06 -0400 ActionableScore: 2 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-2026-89753 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89753 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-2026-89753 LOW https://www.kernelcve.org/list/?q=CVE-2026-89753 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-400;CWE-834;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'shrink_lruvec can spend a long time in reclaim and only called cond_resched inside the scan loop. On PREEMPTION kernels this may not report a Tasks RCU quiescent state, so a reclaiming task can become an RCU Tasks holdout and trigger stall reports. For the CVSS the PR:L is used for the paranoid score because a local user process can create memory pressure that enters direct reclaim, while no administrative privilege is normally required just to allocate memory. The issue is not directly network reachable as a kernel protocol bug, although a remote workload could indirectly increase memory pressure through an exposed service. Impact is denial of service or availability degradation through RCU Tasks stalls and delayed progress. No confidentiality or integrity impact is supported because the patch shows no UAF, OOB access, arbitrary write, or information leak primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES HARDWARE LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2. No floor or cap changed the score. * Raw paranoid score: 2 * Paranoid score: 2. No floor or cap changed the score. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown Positive signals: * +1 Local unprivileged trigger: ordinary local processes can create memory pressure and enter direct reclaim through allocation or page fault paths without host-admin-equivalent privilege. * +1 Availability degradation: the issue can cause RCU Tasks stall reports and delayed progress during reclaim on PREEMPTION kernels. Negative signals: * 0 No host-admin penalty: host-admin-equivalent privilege is not required for the basic memory-pressure path. * 0 No race/timing penalty: this is not scored as a hard race. The issue is an unbounded reclaim loop failing to report Tasks-RCU quiescent states. * 0 No rare-subsystem penalty: vmscan and direct reclaim are core MM paths. Material non-awarded signals: * Remote reachability not awarded. Remote workloads may indirectly cause memory pressure through an exposed service, but the vulnerable operation is not directly reachable as a network protocol bug. * Reliable kernel crash not awarded. The supplied evidence shows RCU Tasks stalls and delayed progress, not a demonstrated panic or fatal kernel crash. * Extra Availability not awarded. The same stall condition is already counted once. * Memory corruption not awarded. The patch shows no UAF, OOB access, stale pointer, double free, arbitrary write, or information leak. * C/I impact not awarded. No confidentiality or integrity primitive is established. * ImportantCandidate not awarded. There is no corruption, ownership, authorization, or security-boundary primitive requiring Important-vs-Moderate preservation. 3. Reachability analysis The likely trigger is local memory pressure that drives allocation, page fault handling, direct reclaim, and shrink_lruvec. An ordinary local user can usually allocate memory and cause reclaim activity, so HostAdminRequired=NO. No namespace-scoped capability is required or relevant to the trigger, so NamespaceScopedPrivilege=NO. There is no evidence of a needed sysctl, boot option, special hardware, or privileged device setup beyond running a kernel configuration where PREEMPTION makes cond_resched ineffective for Tasks-RCU quiescent reporting. The issue is not directly network-triggerable. A remote client could only contribute indirectly if an exposed service allocates enough memory to enter reclaim, which is not a direct attacker-controlled kernel interface for this bug. 4. Primitive and severity interpretation The exact issue is a scheduler/RCU progress accounting bug in the reclaim loop. shrink_lruvec may run for a long time and call cond_resched, but on PREEMPTION kernels that may not report a Tasks-RCU quiescent state. The task can therefore become an RCU Tasks holdout. PrimitiveClass=NONE because there is no kernel memory corruption, stale object use, ownership violation, authorization bypass, or semantic reinterpretation primitive. RealUAF=NO. The demonstrated consequence is availability degradation through RCU Tasks stall reports and delayed RCU progress. The speculative consequence is broader system latency or service degradation under sustained reclaim pressure, but not privilege escalation or data exposure. ImportantCandidate=NO because no Important-grade primitive is established. AutoDowngradeAllowed=YES because the issue is DoS/progress-only and does not contain unresolved corruption or boundary-bypass leverage. Likely operational severity is ordinary Moderate or Low-like depending on environment sensitivity to RCU stall noise and reclaim latency. 5. One-sentence report phrase shrink_lruvec could fail to report Tasks RCU quiescent states during long reclaim loops on PREEMPTION kernels, allowing local memory pressure to cause RCU Tasks stalls and availability degradation without evidence of memory corruption or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a DoS/progress-accounting fix with no demonstrated memory corruption, no UAF, no authorization bypass, no direct network reachability, and no plausible Important-grade primitive in the supplied patch context. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mm/vmscan: report RCU-tasks quiescent states in shrink_lruvec() Commit: b5391676c61d94ffe3272dcf6723738b802f79e8 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5391676c61d94ffe3272dcf6723738b802f79e8 Commit description: I am seeing some rcu_tasks stalls in the Meta fleet during reclaim. INFO: rcu_tasks detected stalls on tasks: 0000000088620d09: .. nvcsw: 6735/6735 holdout: 1 idle_cpu: -1/8 task:GlobalCPUThread state:R running task pid:2552016 tgid:2524552 Call Trace: shrink_lruvec mem_cgroup_iter shrink_node do_try_to_free_pages try_to_free_pages __alloc_frozen_pages_noprof alloc_pages_noprof pte_alloc_one __pte_alloc handle_mm_fault Nothing promises direct reclaim returns in bounded time, and the scan loop in shrink_lruvec() only calls cond_resched(), which is a no-op on PREEMPTION kernels. Involuntary preemption is not a Tasks-RCU quiescent state, so the reclaiming task never reports one and becomes a holdout. Upgrade it to cond_resched_tasks_rcu_qs(), which reports a quiescent state even when cond_resched() does nothing. PS: This has been discussed in [1] Link: https://lore.kernel.org/20260810-rcu_task_shrink_lruvec-v1-1-4d9f7d5251cb@debian.org Link: https://lore.kernel.org/all/amdWVTs0WKOxguxP@gmail.com/ [1] Signed-off-by: Breno Leitao Reviewed-by: Paul E. McKenney Acked-by: Johannes Weiner Acked-by: Shakeel Butt Cc: Axel Rasmussen Cc: Barry Song Cc: David Hildenbrand Cc: Kairui Song Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Wei Xu Cc: Yuanchu Xie Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: mm/vmscan.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=b5391676c61d94ffe3272dcf6723738b802f79e8 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89753 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89753 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: unknown 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).