From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-23097][MODERATE REGULAR] migrate: correct lock ordering for hugetlb file folios Date: Sun, 27 Sep 2026 00:02:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-23097 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 526394af4e8ade89cacd1a9ce2b97712712fcc34 List-Id: CVE: CVE-2026-23097 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: migrate: correct lock ordering for hugetlb file folios Commit: 526394af4e8ade89cacd1a9ce2b97712712fcc34 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=526394af4e8ade89cacd1a9ce2b97712712fcc34 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097 Analysis date: Sun, 27 Sep 2026 00:02:43 -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-2026-23097 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-23097 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-23097 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-833;CWE-667;CWE-362;BEST CVSS score: '4.7';DESCR 'A lock ordering race in hugetlb folio migration can deadlock the kernel because the migration path holds folio_lock and then waits for i_mmap_rwsem while hugetlbfs hole punching can hold i_mmap_rwsem and wait for the same folio_lock. A local user may trigger the condition by operating on an accessible hugetlbfs file while its folios are being migrated, although reliable reproduction depends on hugetlbfs availability, file permissions, concurrent migration, and a narrow timing window. For the CVSS the PR:L value is used because a local user context and access to the affected hugetlbfs object are required, but full administrative control is not necessarily required. The issue is not network reachable. Impact is denial of service through blocked tasks and a possible persistent kernel deadlock. No UAF, out of bounds access, information disclosure, or write primitive is supported by the analyzed code, so confidentiality and integrity remain unaffected.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE READ DEADLOCK DANGER RACE UAF SYZBOT MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable strong DoS. The inverted `folio_lock` and `i_mmap_rwsem` acquisition order establishes an ABBA deadlock that can leave the participating tasks blocked indefinitely. * +0 Local unprivileged trigger. Hole punching may be available to a user with write access to the hugetlbfs file, but the supplied evidence does not establish that the same below-host-admin actor can initiate the required file-folio migration. * +0 Memory corruption. The patch changes lock scope and passes `RMP_LOCKED`. It does not establish a UAF, stale post-lifetime access, OOB operation, overwrite, or invalid free. * +0 Confidentiality and integrity. No disclosure, unauthorized modification, ownership violation, or security-boundary bypass is shown. * +0 Additional availability. The same deadlock is not counted again as a separate availability consequence. * +0 Hard-race penalty. Concurrency is required, but the evidence does not establish a genuinely one-shot or externally uncontrollable race. Repeated hole-punch attempts may enlarge the opportunity. * +0 Rare-subsystem penalty. Hugetlbfs requires relevant configuration and available huge pages, but specialization alone does not justify a negative point. * Controlled reclaim, arbitrary write, privilege escalation, remote reachability, and persistent data corruption are not demonstrated. 3. Reachability analysis The vulnerable sequence requires a file-backed hugetlb folio to undergo migration while another task performs partial hole punching through `hugetlbfs_fallocate()`. A user with write access to the file can plausibly control the hole-punch side, but the supplied context does not prove who controls the migration side or whether an ordinary user can complete both stages in the affected deployment. Hugetlbfs must be available, huge pages must have been provisioned, and the attacker must have access to a suitable file. Some deployments therefore involve prior administrative setup, but that setup is not equivalent to proof that host-admin privilege is required for every trigger. `HostAdminRequired` remains `UNKNOWN`. No user-namespace or network-namespace capability path is involved, and the issue is not network reachable. The timing requires concurrent operations, but repeated attempts appear possible and no concrete hard-race penalty is supported. 4. Primitive and severity interpretation The exact primitive is an ABBA lock-order inversion: `folio_lock` to `i_mmap_rwsem` versus: `i_mmap_rwsem` to `folio_lock` This is a synchronization defect producing deadlock, not a lifetime or memory-corruption primitive. There is no first operation that frees an object, no dangling reference, and no second release or refcount mutation. The demonstrated consequence is blocked migration and hole-punch tasks, with possible broader availability degradation if dependent kernel work also stalls. Privilege escalation and memory corruption are unsupported speculative consequences. `PrimitiveClass=CLASS_C` is appropriate because the behavior is DoS-oriented without an independently useful exploitation primitive. `ImportantCandidate=NO` follows from the absence of corruption, authorization bypass, ownership violation, or cross-boundary impact. `AutoDowngradeAllowed=YES` is appropriate, although deployment-specific reachability should be checked before closure. 5. One-sentence report phrase An ABBA lock-order inversion between hugetlb folio migration and hugetlbfs hole punching can deadlock kernel tasks, causing a local denial of service without an established memory-corruption or privilege-escalation primitive. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Confirm whether an unprivileged user can both access a hugetlbfs file and induce migration of its file-backed huge folios in the evaluated product. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: migrate: correct lock ordering for hugetlb file folios Commit: 526394af4e8ade89cacd1a9ce2b97712712fcc34 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=526394af4e8ade89cacd1a9ce2b97712712fcc34 Commit description: Syzbot has found a deadlock (analyzed by Lance Yang): 1) Task (5749): Holds folio_lock, then tries to acquire i_mmap_rwsem(read lock). 2) Task (5754): Holds i_mmap_rwsem(write lock), then tries to acquire folio_lock. migrate_pages() -> migrate_hugetlbs() -> unmap_and_move_huge_page() <- Takes folio_lock! -> remove_migration_ptes() -> __rmap_walk_file() -> i_mmap_lock_read() <- Waits for i_mmap_rwsem(read lock)! hugetlbfs_fallocate() -> hugetlbfs_punch_hole() <- Takes i_mmap_rwsem(write lock)! -> hugetlbfs_zero_partial_page() -> filemap_lock_hugetlb_folio() -> filemap_lock_folio() -> __filemap_get_folio <- Waits for folio_lock! The migration path is the one taking locks in the wrong order according to the documentation at the top of mm/rmap.c. So expand the scope of the existing i_mmap_lock to cover the calls to remove_migration_ptes() too. This is (mostly) how it used to be after commit c0d0381 . That was removed by 336bf30 for both file & anon hugetlb pages when it should only have been removed for anon hugetlb pages. Link: https://lkml.kernel.org/r/20260109041345.3863089-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Fixes: 336bf30 ("hugetlbfs: fix anon huge page migration race") Reported-by: syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/68e9715a.050a0220.1186a4.000d.GAE@google.com Debugged-by: Lance Yang Acked-by: David Hildenbrand (Red Hat) Acked-by: Zi Yan Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: Jann Horn Cc: Joshua Hahn Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Brost Cc: Rakie Kim Cc: Rik van Riel Cc: Vlastimil Babka Cc: Ying Huang Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: mm/rmap.c mm/migrate.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=526394af4e8ade89cacd1a9ce2b97712712fcc34 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-23097 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097 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: Not available 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: 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).