From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90259][MODERATE REGULAR] btrfs: qgroup: fix a wrong length calculation in qgroup_free_reserved_data() [ Upstream Date: Thu, 17 Sep 2026 14:28:34 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90259 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: e6edde29990af8064b9d12217ec03db231ccd55d List-Id: CVE: CVE-2026-90259 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: btrfs: qgroup: fix a wrong length calculation in qgroup_free_reserved_data() [ Upstream Commit: e6edde29990af8064b9d12217ec03db231ccd55d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e6edde29990af8064b9d12217ec03db231ccd55d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90259 Analysis date: Thu, 17 Sep 2026 14:28:34 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90259 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90259 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90259 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90259 CHECK WITH IMPACT FROM ORIG NN NONE 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:L/A:H';CWE-682;CWE-697;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'A wrong length calculation in btrfs qgroup_free_reserved_data() can make the function treat the rounded end offset as the rounded length. This may cause qgroup reserved data to be freed outside the requested range and can weaken quota accounting for a Btrfs filesystem with qgroups enabled. For the CVSS the PR:L is used because a local user with write access to affected Btrfs files can potentially trigger qgroup reservation and release paths without full administrator privileges. The issue is not network reachable and does not show a memory corruption primitive. Impact is mainly integrity impact against quota policy and possible availability impact from inconsistent quota accounting rather than privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES OOB DISK UAF SKIP INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3. No floor or cap applied. * Raw paranoid score: 4 * Paranoid score: 4. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Positive conservative signals: * +1 Local below-host-admin trigger. Once Btrfs qgroups are enabled and the user has write access to affected files or subvolumes, ordinary filesystem operations can reach qgroup reservation and release paths. * +1 Important filesystem/storage path. The bug is in Btrfs qgroup accounting, which is a storage quota and resource-control mechanism. * +1 Quota policy/accounting impact. The wrong aligned length can free reserved qgroup ranges outside the intended range, plausibly weakening quota enforcement or producing inconsistent accounting. Additional paranoid signal: * +1 Availability concern from sustained quota/accounting inconsistency. In a qgroup-enabled multi-tenant setup, incorrect reservation freeing may contribute to resource exhaustion or quota enforcement failure, but this is not shown as immediate host-wide crash. Non-awarded signals: * +0 Real UAF. No use-after-free, stale pointer, double release, refcount misuse, or lifetime corruption is established. * +0 Memory corruption. The patch fixes arithmetic and range accounting, not an OOB write, arbitrary write, controlled reclaim, or type confusion. * +0 Confidentiality. No disclosure path is shown. * +0 Strong integrity primitive. The issue may affect quota accounting, but there is no demonstrated protected-file overwrite, COW violation, metadata corruption, or authorization bypass. * +0 Reliable kernel crash. No panic, BUG, or filesystem shutdown is established. * +0 Remote reachability. The trigger is local filesystem activity, not network traffic. * +0 Race penalty. This is not a timing race. * +0 Host-admin penalty. Host admin is needed to enable or mount the relevant Btrfs/qgroup environment, but runtime triggering by a user with write access is not shown to require host-admin-equivalent privilege. 3. Reachability analysis The realistic attacker is a local user or workload with write access to a Btrfs filesystem where qgroups are enabled. The relevant operations are ordinary filesystem operations that can create and release qgroup reserved data ranges. Host administrator action may be required as prior setup to mount Btrfs and enable qgroups, but the supplied patch does not show that the vulnerable runtime path itself requires host root. Therefore HostAdminRequired is NO for the trigger model, while prior setup remains deployment-dependent. The issue is not network reachable. No namespace-scoped capability is central to the trigger. No special hardware is required. No race or narrow timing window is involved. 4. Primitive and severity interpretation The primitive is an arithmetic/range-accounting error in `qgroup_free_reserved_data()`. The old code assigned `len = round_up(start + len, sectorsize)`, which stores the rounded end offset as if it were a length. Later use of `start + len` could therefore cover a much larger range than intended. This is Class C: invalid filesystem quota/accounting behavior with potential policy and availability consequences. It is not Class A because there is no concrete authorization bypass, ownership/COW violation, controlled corruption, or LPE chain. It is not Class B because no kernel lifetime, UAF, RCU, refcount, or active stale-object primitive is established. Demonstrated consequence is incorrect qgroup reserved-space freeing. Speculative consequence is weakened quota enforcement or resource exhaustion in qgroup-dependent environments. ImportantCandidate is NO because no Important-grade primitive is established. AutoDowngradeAllowed is YES because there is no unresolved memory-corruption, lifetime, authorization, or ownership primitive, though manual review is still useful for products relying on Btrfs qgroups for tenant isolation. 5. One-sentence report phrase A wrong aligned length calculation in btrfs qgroup_free_reserved_data() can free qgroup reserved ranges outside the requested extent, weakening Btrfs qgroup quota accounting for local users with write access but without showing memory corruption or privilege escalation. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is not memory corruption and is unlikely to be Important by itself, but Btrfs qgroups may be used as a resource isolation mechanism, so environments relying on qgroup quota enforcement should review practical impact. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: btrfs: qgroup: fix a wrong length calculation in qgroup_free_reserved_data() [ Upstream Commit: e6edde29990af8064b9d12217ec03db231ccd55d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e6edde29990af8064b9d12217ec03db231ccd55d Changed files: fs/btrfs/qgroup.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=e6edde29990af8064b9d12217ec03db231ccd55d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90259 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90259 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:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H The Best / paranoid CVSS score: 5.3 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: 3 Paranoid ActionableScore: 4 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).