From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89457][MODERATE REGULAR] s390/dasd: Guard sysfs discipline callbacks against unallocated private data Date: Fri, 11 Sep 2026 23:19:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89457 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 536407b272402af679155910d7fdeeb4834eefb9 List-Id: CVE: CVE-2026-89457 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: s390/dasd: Guard sysfs discipline callbacks against unallocated private data Commit: 536407b272402af679155910d7fdeeb4834eefb9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=536407b272402af679155910d7fdeeb4834eefb9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457 Analysis date: Fri, 11 Sep 2026 23:19:00 -0400 ActionableScore: 3 ActionableScore lower bound: 2 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-2026-89457 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457 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-2026-89457 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89457 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-476;CWE-362;CWE-665;BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in s390 DASD ECKD sysfs discipline callbacks can occur because the discipline may be assigned before device private data is allocated during dasd_generic_set_online. A local user can trigger the bug by reading a world readable sysfs attribute in that timing window, causing the callback to dereference device private while it is still NULL and panic the kernel. For the CVSS the PR:L is used because the attacker needs local user access to read the sysfs attribute, but does not need administrative privileges for the read itself. The issue is not network reachable and depends on a race with device online initialization on affected s390 DASD systems. Impact is denial of service via kernel crash. Confidentiality and integrity impact are not assigned because the observed primitive is a NULL pointer dereference rather than UAF, OOB access, information disclosure, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DANGER SIMPLEFIX HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 3 * Paranoid score: 3 * Final recommended bucket: **Borderline / manual review recommended**:: No floor or cap changed the score. 2. Signal breakdown Positive signals: * +1 Local unprivileged trigger. The supplied description explicitly says an unprivileged read of a world-readable sysfs attribute can hit the vulnerable window. * +1 Reliable kernel crash / strong DoS. The described consequence is NULL pointer dereference and panic. * +1 Weak / indirect corruption candidate. The primitive is an invalid NULL dereference of device->private through DASD discipline callbacks, not a UAF or controlled memory corruption. Negative signals: * -1 Conservative hard timing window. The read must occur after the discipline is assigned but before check_device() allocates device->private during dasd_generic_set_online(). * 0 Paranoid timing penalty withheld. Repeated reads of world-readable sysfs attributes during online initialization could make the timing more reachable than a one-shot uncontrollable race. Important non-awarded signals: * RealUAF not awarded. The object is not freed and reused. The bug is an unallocated private pointer dereference. * Concrete repeated release/refcount not awarded. No first release, surviving dangling reference, or second lifetime mutation is present. * Controlled reclaim not demonstrated. * Arbitrary or directed write not demonstrated. * Confidentiality and integrity not awarded. There is no disclosure path, UAF, OOB access, arbitrary write, or authorization bypass. * Extra availability not awarded. The panic is already counted as the DoS signal. * Rare hardware penalty not applied. The issue is s390 DASD specific, but the affected deployment is exactly that environment and this alone should not erase an unprivileged crash trigger. 3. Reachability analysis The attacker operation is a local read of world-readable DASD sysfs attributes. The supplied evidence supports below-host-admin reachability for the read itself, so HostAdminRequired=NO. The complete trigger also depends on a concurrent device online initialization window in dasd_generic_set_online(). Bringing the DASD device online is normally a privileged device-management operation or an administrator/udev driven event, so the attacker may need to race an existing online transition rather than fully create the condition alone. No namespace-scoped capability path is involved. NamespaceScopedPrivilege=NO. There is no network reachability. The issue is local sysfs control/inspection plane behavior. Special hardware is required in the practical sense because this is s390 DASD ECKD code, but this is treated as deployment scope rather than a strong score-reducing signal. Race repeatability is uncertain. The vulnerable read can likely be retried, but the vulnerable allocation window is narrow and tied to online initialization. 4. Primitive and severity interpretation The exact primitive is a NULL pointer dereference of device->private in DASD ECKD discipline callbacks. This is not active structured UAF and not fixed stale storage. It is an initialization ordering race where callbacks become reachable before private data exists. The demonstrated consequence is local kernel panic / DoS. Speculative consequences beyond crash are not supported by the patch. There is no evidence of controlled replacement, stale post-lifetime object use, refcount mutation, arbitrary write, callback hijack, disclosure, or privilege escalation. PrimitiveClass=CLASS_C because the demonstrated behavior is crash/DoS from invalid state rather than a meaningful corruption or ownership primitive. ImportantCandidate=NO because the patch supports NULL dereference DoS only and does not leave unresolved Important-grade memory corruption leverage. AutoDowngradeAllowed=YES because there is no UAF, no repeated lifetime mutation, no controlled corruption, and no security-boundary bypass. Manual review is still recommended because the trigger is unprivileged local sysfs access and the race affects kernel panic behavior. Likely operational severity is borderline Moderate: serious for affected s390 DASD systems, but not an Important-class kernel exploitation primitive based on supplied evidence. 5. One-sentence report phrase A local unprivileged read of world-readable s390 DASD ECKD sysfs attributes can race device online initialization and dereference unallocated device private data, causing a NULL pointer dereference and kernel panic. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: unprivileged local sysfs reachability and kernel panic are established, but the primitive is NULL dereference only and does not show UAF, memory corruption leverage, information disclosure, integrity impact, or privilege escalation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: s390/dasd: Guard sysfs discipline callbacks against unallocated private data Commit: 536407b272402af679155910d7fdeeb4834eefb9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=536407b272402af679155910d7fdeeb4834eefb9 Commit description: Several sysfs show/store handlers call a discipline callback that dereferences device->private, either directly or through the DASD_DEFINE_ATTR() macro. During dasd_generic_set_online() the discipline is assigned before check_device() allocates device->private, so an unprivileged read of one of these world-readable attributes in that window dereferences a NULL pointer and panics. Guard the dereference inside each callback that actually touches device->private. Fixes: c729696 ("s390/dasd: Recognise data for ESE volumes") Cc: stable@vger.kernel.org Reviewed-by: Jan Höppner Signed-off-by: Stefan Haberland Link: https://patch.msgid.link/20260805111612.1285190-4-sth@linux.ibm.com Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman Changed files: drivers/s390/block/dasd_eckd.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=536407b272402af679155910d7fdeeb4834eefb9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89457 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89457 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: 2 Paranoid ActionableScore: 3 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).