From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93795][LOW] blk-cgroup: fix leaks and online flag on radix_tree_insert failure [ Upstream Date: Thu, 24 Sep 2026 17:50:46 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93795 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 6e85f02d45b5977c0326a8d854c6db878aa6b34a List-Id: CVE: CVE-2026-93795 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: blk-cgroup: fix leaks and online flag on radix_tree_insert failure [ Upstream Commit: 6e85f02d45b5977c0326a8d854c6db878aa6b34a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e85f02d45b5977c0326a8d854c6db878aa6b34a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93795 Analysis date: Thu, 24 Sep 2026 17:50:46 -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-2026-93795 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93795 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-2026-93795 LOW https://www.kernelcve.org/list/?q=CVE-2026-93795 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-401;*CWE-772;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A blk cgroup resource leak can occur if radix_tree_insert fails while creating a blkcg_gq object. The failed path can retain the blkcg_gq object, per CPU I O statistics, policy data, parent references, and a cgroup css reference which may prevent cgroup destruction. Repeated triggering requires a local workload capable of reaching the blk cgroup path and inducing the uncommon radix tree insertion failure condition, typically under memory pressure. For the CVSS the PR:L reflects a local user or delegated cgroup context rather than full system administration. The issue is not network reachable. Impact is local denial of service through accumulated resource consumption and stuck cgroup lifetime. No memory corruption, information disclosure, integrity impact, or privilege escalation primitive is indicated by the patch.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES SIMPLEFIX LEAK ERRORPATH HARDWARE NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap was applied. The supplied patch establishes a persistent resource and reference leak, but does not establish memory corruption, an attacker-controlled lifetime primitive, a reliable host-wide DoS, or below-host-admin reachability. 2. Signal breakdown * +1 Concrete persistent kernel resource/reference leak. When `radix_tree_insert()` fails, `blkg_put()` runs while `blkg->refcnt` remains in percpu mode. The decrement does not invoke `blkg_release()`, permanently retaining the `blkcg_gq`, per CPU I O statistics, policy data, parent `blkcg_gq` reference, and cgroup css reference. * +0 Resource exhaustion impact. The leak is concrete and persistent, and a retained css reference can prevent cgroup destruction. However, the supplied evidence does not demonstrate that a small number of operations causes host-wide exhaustion or a reliable system-wide failure. * +0 Local unprivileged trigger. The supplied patch does not establish that an ordinary local user can complete the full trigger sequence, including reaching the relevant blk cgroup path and causing `radix_tree_insert()` to fail. * +0 Remote reachability. No network-reachable path is established. * +0 Memory corruption. No UAF, stale dereference, double release, out of bounds access, invalid free, or write through freed memory is established. * +0 Confidentiality and integrity. The patch establishes only retained references and leaked allocations. It does not establish disclosure, unauthorized modification, page ownership corruption, or privilege escalation. * +0 Strong DoS. The retained references may accumulate under repeated failures, but the supplied material does not establish a reliable immediate kernel crash, panic, filesystem shutdown, or host-wide resource exhaustion. * No privilege penalty was applied. Host-admin-equivalent privilege is not positively established, but below-host-admin reachability is also not positively established. 3. Reachability analysis The vulnerable path is in `blkg_create()` and requires `radix_tree_insert()` to fail after a `blkcg_gq` has been allocated and partially initialized. The supplied commit identifies the failure handling mechanics but does not provide the complete call chain, capability checks, cgroup delegation conditions, block controller configuration, or a proof that an ordinary user can repeatedly induce the allocation or insertion failure. A local workload operating through a configured blk cgroup environment may plausibly reach this path, especially under memory pressure. That is not sufficient evidence to classify the complete attack path as ordinary-user reachable. Likewise, the presence of cgroups does not prove that all required operations are available in an attacker-controlled cgroup namespace. No network trigger, special hardware requirement, boot parameter, or direct race condition is established. The error condition is uncommon because it depends on `radix_tree_insert()` failure, but no timing penalty is applied because this is an ordered error path rather than a demonstrated narrow race. 4. Primitive and severity interpretation The exact primitive is a persistent resource and reference leak caused by incorrect percpu reference-count shutdown during an error path. `blkg_put()` does not complete normal object release while the reference remains in percpu mode. As a result, `blkg_release()` is not called and the object graph remains retained. This is not an active structured-object UAF and not fixed stale storage. There is no first release that may free an object followed by a second release through the same dangling reference. The patch replaces an ineffective reference decrement with `percpu_ref_kill()` so that the normal release path can execute. Therefore, the concrete repeated release/refcount rule does not apply. The incorrectly set `blkg->online` flag is an invalid-state issue for an object that was never successfully inserted. The available evidence does not show that this flag exposes an active object to later unsafe dereference or corruption. PrimitiveClass is CLASS_C because the demonstrated result is invalid lifecycle state and persistent resource retention without an independently useful corruption primitive. ImportantCandidate is NO because no unresolved UAF, controlled corruption, authorization bypass, cross-boundary impact, or active post-free mutation is established. AutoDowngradeAllowed is YES because this is a constrained leak and error-path cleanup defect with no demonstrated exploitation leverage beyond possible gradual resource consumption. The likely operational severity is Low or ordinary Moderate. Systems that heavily create blk cgroup associations while repeatedly hitting allocation failures may experience retained cgroups and accumulated kernel memory use, but the patch does not support an Important-class interpretation. 5. One-sentence report phrase A failed blk cgroup creation can permanently leak blkcg_gq resources and cgroup references because the percpu reference is decremented without first being killed, potentially causing gradual local resource exhaustion under repeated failure conditions. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a resource leak and blocked cgroup cleanup, but does not establish memory corruption, a security-boundary bypass, reliable host-wide DoS, or a concrete below-host-admin exploit path. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: blk-cgroup: fix leaks and online flag on radix_tree_insert failure [ Upstream Commit: 6e85f02d45b5977c0326a8d854c6db878aa6b34a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e85f02d45b5977c0326a8d854c6db878aa6b34a Changed files: block/blk-cgroup.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=6e85f02d45b5977c0326a8d854c6db878aa6b34a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93795 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93795 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: 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: 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).