From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90426][MODERATE REGULAR] iommu/tegra241-cmdqv: Free the error IRQ before tearing down VINTFs [ Upstream Date: Thu, 17 Sep 2026 14:13:45 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90426 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: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 List-Id: CVE: CVE-2026-90426 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: iommu/tegra241-cmdqv: Free the error IRQ before tearing down VINTFs [ Upstream Commit: 076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90426 Analysis date: Thu, 17 Sep 2026 14:13:45 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A teardown ordering race in the Tegra241 CMDQV IOMMU driver can let an error IRQ handler dereference a NULL or freed VINTF during device removal, causing a host kernel crash, but reliable triggering appears to require host administrator control over physical IOMMU teardown. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90426 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90426 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-2026-90426 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90426 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:H/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A teardown ordering race in the Tegra241 CMDQV IOMMU driver can allow tegra241_cmdqv_isr to observe a VINTF while it is being destroyed. If an error IRQ arrives after VINTF resources are freed but before the IRQ is released, the ISR may pass a NULL or freed pointer into tegra241_vintf0_handle_error and crash the kernel. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over driver removal, device unbind, or equivalent platform management. The issue is not directly network reachable and applies to systems with the NVIDIA Tegra241 Grace CMDQV IOMMU support enabled. Impact is at least local denial of service via kernel crash. In the paranoid score, the freed pointer access in interrupt context is treated as a UAF candidate that may justify confidentiality and integrity impact for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES UAF HARDWARE LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES ## 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap was applied. ## 2. Signal breakdown Conservative signals: * +2 Real UAF / lifetime violation. The patch and commit directly establish that a VINTF can be freed or cleared while `tegra241_cmdqv_isr()` may still observe it and pass a NULL or freed pointer to `tegra241_vintf0_handle_error()`. * +1 Reliable kernel crash / strong DoS. The described consequence is NULL or freed pointer dereference in IRQ context, which realistically supports kernel crash or fatal fault. * -2 Host-admin-equivalent requirement. The affected path is `tegra241_cmdqv_remove()`, i.e. physical IOMMU driver teardown / device removal / platform management, which is host-admin-equivalent in the supplied context. Paranoid additional signal: * +1 Privileged kernel/device-management lifetime corruption concern. The stale object is part of IOMMU CMDQV/VINTF driver state and is consumed from an interrupt handler. This justifies slightly higher manual-review sensitivity, but not Important-class scoring. Important non-awarded signals: * Controlled reclaim is not demonstrated. * Arbitrary or directed kernel write is not demonstrated. * Confidentiality and integrity impact are not awarded from UAF alone. * Remote reachability is not established. * Namespace-scoped triggering is not established. * Structured stale-object exploitation leverage is not awarded because attacker-controlled replacement or attacker-shaped post-free contents are not shown. * Concrete repeated release/refcount mutation is not established. * Extra availability is not awarded because the same crash is already counted. * Rare hardware penalty is not additionally stacked to avoid over-counting deployment restriction already captured by host-admin teardown and specialized platform context. Repeated release/refcount check: * First release can free VINTF state: yes, VINTF teardown can free `vintf0`. * Exact same reference survives to a second lifetime mutation: no evidence. * Second operation mutates lifetime/refcount: no evidence. * Concrete repeated release/refcount +1: not awarded. * Paranoid repeated-refcount +1: not awarded. * FLOOR 5: not applied. ## 3. Reachability analysis The evaluated trigger is host-side physical IOMMU teardown. The vulnerable sequence requires `tegra241_cmdqv_remove()` to run while an error IRQ can still arrive before `free_irq()` has blocked new handlers and waited for in-flight handlers. This is not reachable by ordinary local users. It is not a network-triggered path. It is not shown to be namespace-scoped. The supplied context explicitly says the physical IOMMU is not a pluggable device and teardown is not expected while user-owned `viommu` state is alive. Reliable triggering therefore appears to require host administrator control over driver removal, device unbind, platform teardown, or equivalent system management. Special hardware is required because this is specific to NVIDIA Tegra241 Grace CMDQV IOMMU support. The race window is narrow, but the conservative arithmetic already uses the host-admin requirement as the main reducing factor and does not additionally subtract timing. ## 4. Primitive and severity interpretation The exact primitive is a teardown-ordering race causing post-lifetime use of VINTF state by an IRQ handler. This is a real UAF / stale pointer condition and therefore `PrimitiveClass=CLASS_B`. The stale object is active structured driver state, not merely passive metadata. However, the observed stale use is tied to device removal and interrupt teardown, and the demonstrated result is NULL or freed pointer dereference leading to DoS. There is no evidence of controlled reclaim, callback control, attacker-controlled post-free contents, arbitrary read/write, privilege escalation, or security-boundary bypass. This is closer to a constrained teardown/IRQ UAF than to an Important-preserving exploitation primitive. `ImportantCandidate=NO` because meaningful exploitation leverage beyond crash is not established. `AutoDowngradeAllowed=YES` because the demonstrated issue is host-admin-triggered crash/DoS with no repeated refcount mutation or unresolved strong corruption primitive. Likely operational severity: ordinary Moderate / low-actionability for most environments, but still worth manual review because it is a real UAF in IRQ context in an IOMMU driver. ## 5. One-sentence report phrase A teardown ordering race in the Tegra241 CMDQV IOMMU driver can let an error IRQ handler dereference a NULL or freed VINTF during device removal, causing a host kernel crash, but reliable triggering appears to require host administrator control over physical IOMMU teardown. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is a real UAF / stale pointer in an IRQ handler, but the supplied evidence supports host-admin-gated teardown DoS rather than a below-admin exploitation primitive. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: iommu/tegra241-cmdqv: Free the error IRQ before tearing down VINTFs [ Upstream Commit: 076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 Changed files: drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.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=076a4f5b1fc2016b973a12bc2ebb9b730e5e1e48 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90426 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90426 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:H/PR:H/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.4 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: 1 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: 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).