From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89502][LOW] ring-buffer: Free cpu_buffer::free_page with subbuf_order Date: Sat, 12 Sep 2026 05:21:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89502 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: 1 X-AL-KERNEL-Commit: 77275ccea06eaf297e8e6ac3fc830cb72086379a List-Id: CVE: CVE-2026-89502 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: ring-buffer: Free cpu_buffer::free_page with subbuf_order Commit: 77275ccea06eaf297e8e6ac3fc830cb72086379a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77275ccea06eaf297e8e6ac3fc830cb72086379a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89502 Analysis date: Sat, 12 Sep 2026 05:21:52 -0400 ActionableScore: 2 ActionableScore lower bound: 1 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-2026-89502 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89502 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-2026-89502 LOW https://www.kernelcve.org/list/?q=CVE-2026-89502 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;CWE-762;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The ring buffer free path used free_page for cpu_buffer free_page even though that allocation can use subbuf_order greater than 0. This can free only an order 0 page from a larger allocation and leave the remaining pages leaked when the per CPU ring buffer is destroyed. For the CVSS the PR:L is used in the paranoid case because delegated tracing access, reduced capability root, or a service account with tracing control could exercise this local control plane without being full host root. The issue is not network reachable and requires local ability to configure or destroy tracing ring buffers. Impact is denial of service through memory exhaustion after repeated operations, with no concrete evidence of UAF, OOB write, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-89502 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE TRACE SIMPLEFIX HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. 2. Signal breakdown Positive signals: * +1 Concrete persistent kernel resource leak. `cpu_buffer->free_page` can be allocated with `subbuf_order > 0`, but the old code released it with `free_page()`, effectively freeing only order 0 and leaking the remaining pages. * +1 Paranoid sustained resource exhaustion. If an actor can repeatedly create, resize, or destroy affected ring buffers with larger sub-buffer order, the leak can accumulate and plausibly cause memory pressure or DoS. Negative or non-awarded signals: * No UAF awarded. The patch shows wrong-order freeing and leaked pages, not stale post-lifetime use. * No repeated release/refcount signal. There is no first release followed by a second lifetime mutation on the same dangling reference. * No strong corruption primitive. No OOB write, controlled reclaim, arbitrary write, type confusion, or callback influence is shown. * No C/I impact. The evidence supports availability/resource exhaustion only. * No reliable immediate crash point. The demonstrated issue is a leak, not a direct panic. * No remote reachability. This is tracing/ring-buffer control-plane behavior, not packet or network input. * No host-admin penalty applied because the supplied patch does not fully prove the complete required privilege boundary, although ordinary deployments likely restrict tracing control to root or CAP_SYS_ADMIN. 3. Reachability analysis The likely trigger is local control over tracing ring-buffer configuration, destruction, or resizing in a setup where `subbuf_order` can be greater than 0. In typical systems, tracefs and ftrace/ring-buffer management are administrator-controlled, but the supplied evidence does not fully establish the exact complete user-facing operation and privilege check, so `HostAdminRequired=UNKNOWN` is used rather than assuming host-admin as a scoring penalty. No namespace-scoped trigger is established. There is no evidence that an ordinary user can create a user namespace and perform the full vulnerable tracing operation there. No network trigger, special device input, firmware mediation, or race is involved. 4. Primitive and severity interpretation The primitive is a wrong-order page free causing a persistent kernel memory leak. It is not an active structured-object UAF and not fixed stale storage accessed after free. The demonstrated consequence is resource leakage that can become DoS only through repeated operations. This is `CLASS_C`: primarily DoS/resource exhaustion behavior without an independently useful corruption primitive. `ImportantCandidate=NO` because there is no evidence of memory corruption, security-boundary bypass, privilege escalation, or unresolved lifetime/refcount mutation. `AutoDowngradeAllowed=YES` because the issue is suitable for ordinary Moderate/Low-like handling unless product-specific evidence proves unprivileged repeated triggering at scale. 5. One-sentence report phrase The ring buffer free path used `free_page()` for an allocation that may require `free_pages(..., subbuf_order)`, causing a local resource leak that can accumulate into memory-exhaustion DoS but does not show UAF, corruption, information disclosure, or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a concrete memory/resource leak with no demonstrated corruption primitive, no UAF, no remote reachability, and no security-boundary bypass. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ring-buffer: Free cpu_buffer::free_page with subbuf_order Commit: 77275ccea06eaf297e8e6ac3fc830cb72086379a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77275ccea06eaf297e8e6ac3fc830cb72086379a Commit description: When sub-buffers use an order greater than 0, cpu_buffer->free_page is allocated with subbuf_order. Use the correct order for cpu_buffer->free_page. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260813131152.3589632-2-vdonnefort@google.com Fixes: f9b94da ("ring-buffer: Set new size of the ring buffer sub page") Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260806211306.3704194-1-vdonnefort%40google.com # patch 3 Signed-off-by: Vincent Donnefort Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman Changed files: kernel/trace/ring_buffer.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=77275ccea06eaf297e8e6ac3fc830cb72086379a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89502 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89502 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:L/PR:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 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).