From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-92501][MODERATE REGULAR] ext4: drain in-flight DIO before buffered write fallback [ Upstream Date: Fri, 18 Sep 2026 07:30:19 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-92501 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: fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c List-Id: CVE: CVE-2026-92501 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ext4: drain in-flight DIO before buffered write fallback [ Upstream Commit: fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92501 Analysis date: Fri, 18 Sep 2026 07:30:19 -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-2026-92501 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92501 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-2026-92501 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-92501 CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-362;CWE-367;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'A race in ext4 can occur when direct I/O falls back to buffered I/O while another asynchronous DIO completion is still in flight. The buffered fallback can dirty page cache pages before the later flush and invalidate step, and a concurrent DIO completion can then observe dirty pages during post direct write invalidation. This can trigger a stale pagecache warning and set an EIO error that is later returned by fsync. For the CVSS the PR:L is used because a local user or local process able to perform file I/O on an affected ext4 setup can exercise the relevant path. The issue is not network reachable and does not provide a demonstrated memory corruption primitive. Impact is mainly denial of service and limited integrity impact through failed or inconsistent write completion reporting.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES WRITE OOB DISK RACE HARDWARE LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP YES 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 Conservative signals: * +1 Local unprivileged trigger. A local user or process that can perform file I/O on an affected ext4 setup can reach the DIO plus buffered fallback path. * +1 Important filesystem/storage path. The issue is in ext4 direct I/O, buffered write fallback, page cache invalidation, and fsync error reporting. * +1 Availability or operational DoS impact. The demonstrated consequence is a stale pagecache warning and errseq_set(-EIO), causing later fsync to return -EIO and potentially fail applications. Paranoid additional signal: * +1 Broader practical trigger concern. The commit states the issue can occur through normal I/O paths, including loop-device backed I/O and block_size smaller than folio_size, not only through a narrow synthetic overlapping-DIO reproducer. Non-awarded signals: * RealUAF not awarded. No freed object or post-lifetime object use is established. * Memory corruption not awarded. The patch shows stale pagecache invalidation state and EIO reporting, not OOB access, UAF, arbitrary write, or controlled corruption. * Confidentiality not awarded. No disclosure path is shown. * Strong integrity corruption not awarded. The evidence supports failed or inconsistent write completion reporting, but not unauthorized modification of another file, protected storage, metadata ownership, or COW state. * Reliable kernel crash not awarded. The demonstrated effect is warning plus fsync -EIO, not panic or host-wide fatal fault. * Race penalty not applied. Although this is a race, the commit states it can be made highly reproducible and can occur through normal I/O paths. * Remote reachability not awarded. This is local filesystem I/O, not network-triggered behavior. 3. Reachability analysis The practical trigger is local file I/O on an affected ext4 filesystem, especially involving direct I/O, fallback to buffered I/O, no-extent inodes, holes, and concurrent asynchronous DIO completion. A normal local process with permission to write the target file can plausibly exercise the relevant path, so host administrator privilege is not required for the vulnerable operation itself. There is prior environmental dependence: the system must have an affected ext4 configuration and workload conditions such as no-extent inodes or folio sharing. That is not the same as host-admin-only reachability, because once such a filesystem and file are available, the operation is ordinary file I/O. No namespace-scoped capability is needed or established. No special hardware is required. The race is timing-dependent, but the commit explicitly says a small delay makes it almost always reproducible and that normal I/O paths can trigger it, so it should not be treated as a hard one-shot race. 4. Primitive and severity interpretation The exact primitive is a filesystem synchronization race between in-flight direct I/O completion and buffered write fallback. The buffered fallback dirties page-cache pages, while a concurrent DIO completion can run post-direct-write invalidation and observe dirty pages. That produces a stale pagecache warning and records EIO, which can later be returned by fsync. This is not an active structured UAF, not fixed stale storage after free, and not a concrete repeated release/refcount mutation. It is best classified as CLASS_C: invalid filesystem/page-cache state with demonstrated DoS or I/O error behavior, but without an independently useful kernel corruption primitive. The demonstrated consequence is local denial of service or operational failure for affected I/O, with limited data-integrity concern through failed or inconsistent write completion reporting. The speculative consequence would be broader filesystem data-integrity impact under real workloads, but the supplied evidence does not establish protected-file corruption, COW ownership violation, arbitrary write, or privilege escalation. ImportantCandidate=NO because no Class A primitive, UAF, ownership bypass, security-boundary bypass, or strong corruption primitive is established. AutoDowngradeAllowed=YES because this is a Class C filesystem race without unresolved memory-corruption or authorization leverage, although manual review is still recommended due to filesystem integrity semantics. Likely operational severity: borderline to actionable Moderate depending on product reliance on affected ext4 DIO workloads. 5. One-sentence report phrase A race in ext4 direct I/O fallback can let buffered writes dirty page cache while another asynchronous DIO completion performs post-write invalidation, causing stale pagecache warnings and fsync EIO failures through local file I/O. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because the bug affects ext4 writeback, page cache invalidation, and fsync error semantics, and the commit states it can be triggered through normal I/O paths. It is not marked required because no UAF, memory corruption, authorization bypass, or privilege escalation primitive is established. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ext4: drain in-flight DIO before buffered write fallback [ Upstream Commit: fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c Changed files: fs/ext4/file.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=fd7e0dab20837b9ea1eeef7c26f78ace8ac8258c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-92501 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92501 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: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).