From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90271][LOW] arm_mpam: Fix a NULL pointer dereference on unbinding after an error interrupt [ Upstream Date: Thu, 17 Sep 2026 19:27:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90271 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: a29044c9c83513c7463de2adb84c169685562ad2 List-Id: CVE: CVE-2026-90271 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: arm_mpam: Fix a NULL pointer dereference on unbinding after an error interrupt [ Upstream Commit: a29044c9c83513c7463de2adb84c169685562ad2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a29044c9c83513c7463de2adb84c169685562ad2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90271 Analysis date: Thu, 17 Sep 2026 19:27:31 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A NULL pointer dereference in the ARM MPAM MSC remove path can be triggered when a host administrator unbinds an MSC after an error interrupt has caused `mpam_disable()` to clear driver data, leading to local DoS only. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90271 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90271 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-2026-90271 LOW https://www.kernelcve.org/list/?q=CVE-2026-90271 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.4';DESCR 'A NULL pointer dereference in the ARM MPAM MSC driver remove path can occur when an MSC is unbound after mpam_disable has already run in response to an error interrupt and cleared the platform drvdata. The remove callback then receives a NULL msc pointer and may dereference it during cleanup, causing a kernel crash or oops. For the CVSS the PR:H is used because triggering the vulnerable remove callback normally requires administrative access to unbind a platform device through sysfs or otherwise control driver binding. The issue is not network reachable and is a local control plane failure path. Impact is denial of service only, with no evidence of information disclosure, integrity impact, UAF, OOB access, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES NULLPTR SIMPLEFIX DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES ## 1. ActionableScore * Raw conservative score: -1 * Conservative score: 0 * Raw paranoid score: -1 * Paranoid score: 0 * Applied conservative floor/cap: minimum score floor -1 -> 0 * Applied paranoid floor/cap: minimum score floor -1 -> 0 * Final recommended bucket: **Ordinary Moderate**:: ## 2. Signal breakdown * +1 Reliable kernel crash / strong DoS: after `mpam_disable()` clears platform `drvdata`, `mpam_msc_drv_remove()` can receive `msc == NULL` and dereference it during remove cleanup. * -2 Full host-admin-equivalent privilege: triggering the vulnerable remove callback requires unbinding a platform device / controlling driver binding through sysfs or equivalent host device-management authority. * +0 Weak corruption concern: this is a NULL pointer dereference, not an established UAF, OOB access, double release, refcount mutation, arbitrary write, or controlled memory corruption. * +0 Remote reachability not awarded: no network path is involved. * +0 C/I not awarded: no disclosure path, unauthorized modification, ownership violation, or privilege-escalation primitive is established. * +0 Extra availability not awarded: the same crash/oops is already counted once. * +0 Hardware rarity penalty not applied: ARM MPAM hardware is platform-specific, but the host-admin requirement already captures the main practical restriction and no additional penalty is needed. No concrete repeated release/refcount case exists: * First release can end lifetime: not applicable. * Exact same reference survives: not applicable. * Second lifetime/refcount mutation: not established. * Concrete repeated release/refcount +1: not awarded. * Paranoid repeated-refcount leverage +1: not awarded. * FLOOR 5: not applied. ## 3. Reachability analysis The trigger is local control-plane device management. The described sequence is: an MPAM error interrupt causes `mpam_disable()` to run and clear driver data, then a user unbinds the MSC device and invokes the driver remove callback. In normal Linux systems, unbinding a platform device via sysfs is a host administrator operation, not an ordinary user or namespace-scoped capability operation. `HostAdminRequired=YES` because the complete trigger requires host-level driver/device binding control. `NamespaceScopedPrivilege=NO` because platform device unbind is not a user/network namespace scoped operation. No prior network exposure is relevant. The error interrupt is an additional state prerequisite, but this is an ordered failure-state sequence rather than an attacker-controlled race. ## 4. Primitive and severity interpretation The exact primitive is a NULL pointer dereference in a driver remove path. It is not a real UAF, not fixed stale storage, and not active structured stale-object reuse. The stale or missing state is simply `platform_get_drvdata(pdev)` returning NULL after `mpam_disable()` cleared it. This is cleanup/remove-path invalid-state behavior with demonstrated consequence of kernel oops or crash. There is no concrete post-lifetime object use, no second refcount mutation, no controlled reclaim, no attacker-controlled replacement object, no callback control, and no arbitrary read/write. Therefore `PrimitiveClass=CLASS_C`. `ImportantCandidate=NO` because the evidence supports host-admin-triggered DoS only. `AutoDowngradeAllowed=YES` because no unresolved memory-corruption, authorization-bypass, ownership, or security-boundary primitive remains. ## 5. One-sentence report phrase A NULL pointer dereference in the ARM MPAM MSC remove path can be triggered when a host administrator unbinds an MSC after an error interrupt has caused `mpam_disable()` to clear driver data, leading to local DoS only. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: host-admin-triggered NULL dereference only, with no UAF, repeated lifetime mutation, C/I impact, network reachability, or privilege-escalation evidence. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: arm_mpam: Fix a NULL pointer dereference on unbinding after an error interrupt [ Upstream Commit: a29044c9c83513c7463de2adb84c169685562ad2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a29044c9c83513c7463de2adb84c169685562ad2 Changed files: drivers/resctrl/mpam_devices.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=a29044c9c83513c7463de2adb84c169685562ad2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90271 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90271 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.4 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: 0 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).