From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98259][LOW] fs/dax: check zero or empty entry before converting xarray entry Date: Sat, 10 Oct 2026 14:39:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98259 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: unknown X-AL-KERNEL-Commit: 44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 List-Id: CVE: CVE-2026-98259 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: fs/dax: check zero or empty entry before converting xarray entry Commit: 44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98259 Analysis date: Sat, 10 Oct 2026 14:39:26 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: An empty or zero filesystem DAX xarray entry can be converted into an invalid folio pointer before type validation, causing a local kernel paging fault and panic on systems using affected DAX storage. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98259 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98259 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-2026-98259 LOW https://www.kernelcve.org/list/?q=CVE-2026-98259 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) 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-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'An invalid folio pointer can be produced in the filesystem DAX path because dax_to_folio() is called before checking whether an xarray entry represents an empty or zero DAX entry. A later dereference can generate a kernel paging fault followed by an Oops and kernel panic, as demonstrated during a DAX page fault while booting from DAX enabled storage. For the CVSS the PR:L is selected because a local user or process with access to a suitable DAX backed file or mapping may be able to initiate the fault without holding full administrative privileges. DAX enabled storage and an affected entry state are required preconditions. The issue is not network reachable and there is no demonstrated UAF, OOB write, information leak, or arbitrary write primitive. Impact is denial of service through a kernel crash. Confidentiality and integrity remain unaffected because the observed primitive is an invalid pointer read rather than memory corruption.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE OOB DANGER DISK HARDWARE BOOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO ## 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: ## 2. Signal breakdown Positive signals: * +1 Reliable kernel crash. Converting an empty or zero DAX entry with `dax_to_folio()` produces an invalid folio pointer and causes a demonstrated kernel paging fault, Oops, and panic. * +1 Important filesystem and storage path. The defect is in the filesystem DAX fault and folio-association path and can prevent a DAX-backed system from booting. No negative points were applied: * DAX-enabled storage is an explicit prerequisite, but specialization alone does not establish the rare-and-difficult condition required for a negative point. * Host-admin privilege for the complete trigger is unresolved, so no privilege penalty was applied. Important non-awarded signals: * No UAF, stale lifetime use, OOB write, repeated release, or refcount mutation is established. * No arbitrary or directed write, controlled reclaim, disclosure, or authorization bypass is demonstrated. * No local-unprivileged bonus was awarded because the trace demonstrates PID 1 triggering the fault, not a complete ordinary-user attack path. * No extra Availability point was awarded because it would duplicate the demonstrated panic. * NEW52 B5-R does not apply. There is no retry-accumulated heap OOB write or later consumption of corrupted descriptors. * NEW53 B3-PENDING does not apply. No shared-backing write is present. * NEW54 B4-PENDING does not apply. No DENY-to-ALLOW authorization decision changes. ## 3. Reachability analysis The demonstrated trigger is a local DAX page fault during boot from DAX-enabled storage. DAX provisioning and mount configuration are prior system prerequisites, but the evidence does not establish whether every later vulnerable fault requires host-admin powers. An ordinary user might reach related fault paths through an accessible DAX-backed mapping, but the supplied evidence does not prove that such a user can reliably create the required empty or zero entry state. Therefore `HostAdminRequired` remains `UNKNOWN`, and no local-unprivileged point is awarded. No network or namespace-scoped trigger is established. No race or timing window is required. DAX-capable storage or an equivalent virtual DAX configuration is required. ## 4. Primitive and severity interpretation The exact primitive is premature semantic conversion of an encoded empty or zero DAX xarray entry into a `struct folio` pointer. The conversion path accesses an invalid address before the existing entry-type guard can return. This is an invalid-pointer read leading directly to a fault, not a heap UAF, OOB write, type-confusion primitive, or active-state ownership violation. There is no second lifetime operation and no evidence that corrupted state survives for later security-relevant consumption. The patch-supported consequence is kernel panic and denial of service. Stronger consequences such as disclosure, persistent filesystem corruption, privilege escalation, or arbitrary kernel access are unsupported. The issue is therefore `CLASS_C`, is not an Important candidate, and may be automatically downgraded after ordinary remediation handling. ## 5. One-sentence report phrase An empty or zero filesystem DAX xarray entry can be converted into an invalid folio pointer before type validation, causing a local kernel paging fault and panic on systems using affected DAX storage. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a direct crash-only invalid-pointer path without UAF, writable corruption, authorization bypass, or unresolved ownership primitive. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: fs/dax: check zero or empty entry before converting xarray entry Commit: 44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 Commit description: Calling dax_to_folio() with empty entry causes kernel panic below when booting a VM with DAX enabled storage. This patch checks empty entry before calling dax_to_folio() on dax_associate_entry(), dax_disassociate_entry(), and dax_busy_page(). Commit 98c183a ("fs/dax: don't disassociate zero page entries") added guards in the associate and disassociate paths, but the guards still come after dax_to_folio(), and dax_busy_page() still has the same problem. [ 0.737679] EXT4-fs (pmem0p1): mounted filesystem 79676804-7c8b-491a-b2a6-9bae3c72af70 ro with ordered data mode. Quota mode: disabled. [ 0.737891] VFS: Mounted root (ext4 filesystem) readonly on device 259:1. [ 0.739119] devtmpfs: mounted [ 0.739476] Freeing unused kernel memory: 1920K [ 0.740156] Run /sbin/init as init process [ 0.740229] with arguments: [ 0.740286] /sbin/init [ 0.740321] with environment: [ 0.740369] HOME=/ [ 0.740400] TERM=linux [ 0.743162] Unable to handle kernel paging request at virtual address fffffdffbf000008 [ 0.743285] Mem abort info: [ 0.743316] ESR = 0x0000000096000006 [ 0.743371] EC = 0x25: DABT (current EL), IL = 32 bits [ 0.743444] SET = 0, FnV = 0 [ 0.743489] EA = 0, S1PTW = 0 [ 0.743545] FSC = 0x06: level 2 translation fault [ 0.743610] Data abort info: [ 0.743656] ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000 [ 0.743720] CM = 0, WnR = 0, TnD = 0, TagAccess = 0 [ 0.743785] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 [ 0.743848] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000b9d17000 [ 0.743931] [fffffdffbf000008] pgd=10000000bfa3d403, p4d=10000000bfa3d403, pud=1000000040bfe403, pmd=0000000000000000 [ 0.744070] Internal error: Oops: 0000000096000006 [#1] SMP [ 0.748888] CPU: 0 UID: 0 PID: 1 Comm: init Not tainted 6.18.4 #1 NONE [ 0.749421] pstate: 004000c5 (nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 0.749969] pc : dax_disassociate_entry.constprop.0+0x20/0x50 [ 0.750444] lr : dax_insert_entry+0xcc/0x408 [ 0.750802] sp : ffff80008000b9e0 [ 0.751083] x29: ffff80008000b9e0 x28: 0000000000000000 x27: 0000000000000000 [ 0.751682] x26: 0000000001963d01 x25: ffff0000004f7d90 x24: 0000000000000000 [ 0.752264] x23: 0000000000000000 x22: ffff80008000bcc8 x21: 0000000000000011 [ 0.752836] x20: ffff80008000ba90 x19: 0000000001963d01 x18: 0000000000000000 [ 0.753407] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 [ 0.753970] x14: ffffbf3154b9ae70 x13: 0000000000000000 x12: ffffbf3154b9ae70 [ 0.754548] x11: ffffffffffffffff x10: 0000000000000000 x9 : 0000000000000000 [ 0.755122] x8 : 000000000000000d x7 : 000000000000001f x6 : 0000000000000000 [ 0.755707] x5 : 0000000000000000 x4 : 0000000000000000 x3 : fffffdffc0000000 [ 0.756287] x2 : 0000000000000008 x1 : 0000000040000000 x0 : fffffdffbf000000 [ 0.756871] Call trace: [ 0.757107] dax_disassociate_entry.constprop.0+0x20/0x50 (P) [ 0.757592] dax_iomap_pte_fault+0x4fc/0x808 [ 0.757951] dax_iomap_fault+0x28/0x30 [ 0.758258] ext4_dax_huge_fault+0x80/0x2dc [ 0.758594] ext4_dax_fault+0x10/0x3c [ 0.758892] __do_fault+0x38/0x12c [ 0.759175] __handle_mm_fault+0x530/0xcf0 [ 0.759518] handle_mm_fault+0xe4/0x230 [ 0.759833] do_page_fault+0x17c/0x4dc [ 0.760144] do_translation_fault+0x30/0x38 [ 0.760483] do_mem_abort+0x40/0x8c [ 0.760771] el0_ia+0x4c/0x170 [ 0.761032] el0t_64_sync_handler+0xd8/0xdc [ 0.761371] el0t_64_sync+0x168/0x16c [ 0.761677] Code: f9453021 f2dfbfe3 cb813080 8b001860 (f9400401) [ 0.762168] ---[ end trace 0000000000000000 ]--- [ 0.762550] note: init[1] exited with irqs disabled [ 0.762631] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b Link: https://lore.kernel.org/m2y0enxtzk.fsf@arm.com Fixes: 38607c6 ("fs/dax: properly refcount fs dax pages") Signed-off-by: Seunguk Shin Reviewed-by: Jan Kara Reviewed-by: Alistair Popple Reported-by: Kiara Grouwstra Cc: Al Viro Cc: Christian Brauner Cc: Matthew Wilcox (Oracle) Cc: Signed-off-by: Andrew Morton [Commit description truncated; see the upstream URL below] Changed files: fs/dax.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=44ab7420ab52ab6c04bf225cac7c5c007cedd6c7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98259 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98259 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: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: unknown 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).