From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89578][LOW] dm-io: clone the source bio instead of copying its biovec Date: Sat, 12 Sep 2026 02:55:57 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89578 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: 9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 List-Id: CVE: CVE-2026-89578 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: dm-io: clone the source bio instead of copying its biovec Commit: 9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89578 Analysis date: Sat, 12 Sep 2026 02:55:57 -0400 ActionableScore: 2 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-2026-89578 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89578 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-2026-89578 LOW https://www.kernelcve.org/list/?q=CVE-2026-89578 CHECK WITH IMPACT FROM ORIG NN LOW 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-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in dm-io because DM_IO_BIO handling rebuilt destination bios by walking the source biovec with sector based accounting. Byte granular bvec lengths do not have to be sector aligned, so a misaligned O_DIRECT buffer split across pages can lose a sub-sector remainder and make the outer loop spin forever while submitting empty bios. For the CVSS the PR:L value is used because triggering requires local code execution and access to perform I/O on a file or block device backed by the affected device mapper configuration. The issue is not network reachable and does not provide a clear memory corruption primitive. Impact is denial of service through a hung I/O path, especially on dm-mirror setups with misaligned direct I/O.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-89578 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DISK INIT HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2. No floor or cap applied. * Raw paranoid score: 2 * Paranoid score: 2. No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Local below-host-admin trigger. A local user or process with access to a file or block device backed by the affected dm-mirror or dm-io configuration can plausibly issue misaligned O_DIRECT I/O without host-admin-equivalent privilege. * +1 Availability impact. The established consequence is an infinite loop or stuck I/O path caused by sector-truncated accounting of byte-granular bvec fragments. * +0 Memory corruption not awarded. The patch establishes accounting loss and an infinite loop, not UAF, OOB access, arbitrary write, stale pointer use, or object lifetime corruption. * +0 Confidentiality and integrity not awarded. No disclosure path, protected object modification, filesystem ownership bypass, metadata corruption, or COW violation is established. * +0 Extra availability not awarded. The same I/O hang is already counted once and there is no distinct persistent data-loss or host-wide crash consequence. * +0 Resource leak signal not awarded. The bug submits empty bios in a loop, but the patch does not establish a persistent unrecoverable reference or object leak as the primary primitive. * +0 Important filesystem/storage corruption not awarded. The code is in an important storage path, but the demonstrated bug is a DoS-only progress/accounting failure rather than storage metadata corruption or cross-object integrity impact. * -0 No host-admin penalty applied. Host-admin-equivalent privilege is not positively required for the I/O operation once the affected device stack is present. * -0 No rare hardware or niche subsystem penalty applied. Device mapper and direct I/O are ordinary kernel storage mechanisms, though the vulnerable manifestation depends on dm-mirror-like configuration and misaligned O_DIRECT. 3. Reachability analysis The evaluated attacker is a local user or local process that can perform I/O against a file or block device backed by the affected device-mapper path. The triggering condition is misaligned O_DIRECT I/O whose bio-backed bvec lengths are byte-granular and not sector-aligned. The vulnerable path depends on an existing device-mapper setup, such as dm-mirror, which is normally provisioned by an administrator. That prior setup limits real-world exposure, but the supplied evidence does not show that the attacker must be host admin to trigger the bug after such a device is available. This is not network reachable. No namespace-scoped capability is relevant. No special hardware is required. This is not a race. The trigger is a deterministic accounting/progress bug under the right I/O shape. 4. Primitive and severity interpretation The exact primitive is a progress/accounting logic error in DM_IO_BIO handling. The old code rebuilt destination bios by walking the source biovec and tracking remaining transfer in sectors. Because bvec lengths are byte-granular, to_sector() can truncate a sub-sector remainder and prevent forward progress, causing the outer loop to spin while submitting empty bios. PrimitiveClass is CLASS_C because the established behavior is DoS/invalid-progress behavior without an independently useful corruption, ownership, lifetime, or authorization primitive. There is no real UAF. There is no concrete repeated release or refcount mutation. There is no active structured stale-object use. There is no controlled reclaim, arbitrary kernel read/write, callback control, or boundary bypass. The practical consequence is local denial of service through a hung I/O path. The likely operational severity is ordinary Moderate because the issue can be disruptive but remains DoS-only and configuration-dependent. ImportantCandidate=NO because no Important-grade primitive is established. AutoDowngradeAllowed=YES because no unresolved memory-corruption, lifetime, authorization, ownership, or security-boundary primitive remains. 5. One-sentence report phrase A local DoS can occur in dm-io when misaligned O_DIRECT bio-backed I/O loses a sub-sector biovec remainder during sector-based accounting, causing the I/O path to spin while submitting empty bios. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch supports a DoS-only accounting/progress bug with no memory corruption, no UAF, no C/I impact, no network reachability, and no unresolved Important-grade primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: dm-io: clone the source bio instead of copying its biovec Commit: 9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 Commit description: For DM_IO_BIO requests, do_region() built each destination bio by walking the source bio's biovec and re-adding the pages one at a time, tracking the remaining transfer in sectors. The vector lengths are byte granular and need not be sector aligned (e.g. a misaligned O_DIRECT buffer split across pages), so the sector-based accounting could lose a sub-sector fragment: to_sector() truncated the remainder and the outer loop spun forever submitting empty bios, hanging the I/O. There is no need to rebuild the biovec at all. The destination reads into (or writes from) exactly the same pages as the source bio, so the bio can simply clone the source's biovec with bio_alloc_clone() and remap it to the target device. The clone inherits the source's iterator and alignment, and the block layer splits it to the target's limits on submission, so the whole region maps to a single cloned bio with no manual page copying or sector accounting. This removes the per-page copy path (and its open-coded bvec dpages helpers) for bio-backed I/O and fixes the hang on misaligned direct I/O to a dm-mirror device. Page-list, vma and kmem sources keep the existing copy path. Fixes: 7eac331 ("iomap: simplify direct io validity check") Fixes: 5ff3f74 ("block: simplify direct io validity check") Cc: stable@vger.kernel.org Reported-by: Dr. David Alan Gilbert Reported-by: Vjaceslavs Klimovs Signed-off-by: Keith Busch Signed-off-by: Mikulas Patocka Signed-off-by: Greg Kroah-Hartman Changed files: drivers/md/dm-io.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=9493ac67623d45b7d4671d2b0b4d0633c2bc2e51 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89578 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89578 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).