From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45895][LOW] quota: fix livelock between quotactl and freeze_super [ Upstream Date: Wed, 27 May 2026 22:42:56 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45895 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: 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 List-Id: CVE: CVE-2026-45895 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: quota: fix livelock between quotactl and freeze_super [ Upstream Commit: 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895 Analysis date: Wed, 27 May 2026 22:42:56 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A quota retry loop can livelock with filesystem freeze on non-preemptible kernels, preventing RCU progress and causing a local filesystem administration DoS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45895 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895 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-2026-45895 LOW CHECK 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-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A quota livelock can occur when quotactl_block() spins in a retry loop while freeze_super() waits for RCU progress through percpu_down_write(). On non preemptible kernels the quota loop may not yield the CPU, preventing an RCU quiescent state and leaving the freezer stuck. For the CVSS the PR:L is used in the paranoid score because delegated filesystem administration or service accounts may be able to run quota and freeze operations below full host root, while typical host triggering requires CAP_SYS_ADMIN. The issue is not network reachable. Impact is denial of service through filesystem freeze hang and 100 percent CPU usage. No supported evidence indicates information disclosure, integrity impact, kernel memory corruption, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) MAYBE WRITE OOB DISK HARDWARE LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown * Reliable DoS / livelock: +1 The issue can livelock `quotactl_block()` against `freeze_super()`, causing the freezer to hang and the quota process to consume 100 percent CPU. * Availability impact realistic: +1 The realistic impact is local filesystem administration DoS through stuck freeze or quota operations. * Local delegated filesystem administration: +1 in paranoid scoring Some environments may delegate quota or filesystem administration to service accounts or containerized management components. * Requires CAP_SYS_ADMIN in typical deployments: -2 conservative Reliable triggering normally requires filesystem freeze and quota on/off operations, which are privileged host administration actions. * Special configuration / scheduling condition: -1 in conservative interpretation The livelock is most relevant on non-preemptible kernels or when both loops are pinned to the same CPU. The reproducer is reliable, but the conditions are still administrative and environment-specific. * No memory corruption: +0 This is a scheduling/RCU progress livelock, not UAF, OOB write, arbitrary write, or object lifetime corruption. * No confidentiality or integrity impact: +0 The patch does not indicate data disclosure, filesystem metadata corruption, or privilege escalation. ## 3. Reachability analysis The bug is reachable by running filesystem freeze/unfreeze concurrently with quota on/off against a quota-enabled filesystem. In ordinary deployments this requires privileged filesystem administration, typically `CAP_SYS_ADMIN`. Namespaces or containers only matter if quota/freeze operations are delegated to less trusted service accounts or container root. The issue is not network reachable. Realistic exploitation is local DoS only. ## 4. Severity interpretation This behaves like ordinary Moderate / Low-like availability impact. It can cause a real hang and CPU spin, but it requires privileged filesystem-management operations and does not involve memory corruption or privilege escalation. The paranoid score only accounts for delegated administration environments. ## 5. One-sentence report phrase A quota retry loop can livelock with filesystem freeze on non-preemptible kernels, preventing RCU progress and causing a local filesystem administration DoS. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The issue is a local privileged livelock with no memory corruption, no remote reachability, and no privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: quota: fix livelock between quotactl and freeze_super [ Upstream Commit: 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 Changed files: fs/quota/quota.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=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45895 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895 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:H 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).