From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98343][MODERATE REGULAR] dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() [ Upstream Date: Sat, 10 Oct 2026 08:37:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98343 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: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: b92c502595336a3cc5bb7a060170891366745a5d List-Id: CVE: CVE-2026-98343 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() [ Upstream Commit: b92c502595336a3cc5bb7a060170891366745a5d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b92c502595336a3cc5bb7a060170891366745a5d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98343 Analysis date: Sat, 10 Oct 2026 08:37:32 -0400 ActionableScore: 4 ActionableScore lower bound: unknown 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-2026-98343 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98343 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-2026-98343 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98343 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-825;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free occurs in dma_chan_put() when dma_device_put() drops the final device reference and frees the dma_device and its channels before dma_chan_to_owner() reads chan device owner. The stale owner value is then passed to module_put(), so the confirmed primitive is an invalid read from freed memory followed by a possible reference count operation through a stale module pointer. The demonstrated impact is a kernel warning or crash and denial of service. In a worst case allocator reuse could turn the stale pointer use into memory corruption with confidentiality, integrity, or privilege escalation impact. For the CVSS the PR:L value is used for the paranoid score because a local process or restricted service with delegated device access may be able to exercise a DMA channel release path without having unrestricted host root privileges. Reliable triggering still depends on a suitable DMA provider, reaching the final device reference, and a release path that frees the channels, so AC:H is appropriate. The issue is not directly network reachable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE READ UAF HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 3 * Conservative score: 4 * Raw paranoid score: 3 * Paranoid score: 4 * Applied conservative floor: 3 -> 4 under REAL UAF FLOOR 4 because a freed active object is actually dereferenced and host-admin-equivalent privilege is not positively established. * Applied paranoid floor: 3 -> 4 for the same reason. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Positive signals: * +2 Real UAF. `dma_device_put()` can drop the final reference and free the `dma_device` and its channels. `dma_chan_put()` then dereferences the freed channel and device through `dma_chan_to_owner()`. * +1 Reliable kernel crash or strong DoS. KASAN confirms a slab use-after-free read, and an invalid value can subsequently reach `module_put()`. No negative points: * The `insmod` task name suggests a privileged observed context, but it does not prove that every complete trigger requires host-admin-equivalent privilege. * No race penalty applies. The defect is an ordered lifetime sequence rather than a demonstrated narrow timing race. * No hardware or niche-subsystem penalty applies because special or rare hardware is not established. Material non-awarded signals: * Controlled reclaim and attacker-controlled replacement contents are not demonstrated. * Arbitrary or directed kernel write is not demonstrated. * Structured stale-object leverage is not awarded because attacker influence over reclaimed `dma_device` or channel storage is not established. * Strong or weak LPE leverage is not awarded merely from the UAF. * Confidentiality and integrity points are not awarded. The patch establishes an internal stale read but no disclosure or controlled state modification. * No additional Availability point is awarded because it would double-count the same possible crash. * Remote reachability and local unprivileged reachability are not established. * This is not a concrete repeated-release case. `dma_device_put()` operates on the DMA device, while the later `module_put()` operates on a separately referenced module object. * The exact same dangling object does not receive a second verified lifetime mutation. Therefore the dedicated repeated-release +1 is withheld. * Paranoid repeated-refcount leverage is withheld because no second refcount mutation through the exact freed `dma_device` or channel is established. * FLOOR 5 is not applied. * B5-R, B3-PENDING, and B4-PENDING do not apply. 3. Reachability analysis The observed report occurred in a task named `insmod`, which is consistent with privileged driver or module lifecycle activity. However, the supplied context does not identify the complete caller chain or prove that module loading is the only way to reach the final DMA channel release. No ordinary-user ioctl, namespace-scoped capability path, delegated device-management interface, or remote trigger is established. Conversely, absence of such evidence does not prove that host administration is universally required. Therefore both host-admin and namespace-scoped reachability remain unknown, and no privilege bonus or penalty is applied. No timing race is required by the shown sequence. The necessary condition is that decrementing the final channel client count also drops the final DMA device reference and frees storage before the owner lookup. 4. Primitive and severity interpretation The exact primitive is a heap use-after-free read from an active structured DMA channel or device object. The stale access occurs in a release path after the final device reference may have freed both the device and its channels. This is broader than fixed asynchronous stale storage, but the demonstrated stale use is still narrow. It reads the module owner field and passes the resulting value to `module_put()`. If the freed storage remains unchanged, the intended module pointer may still be obtained. If it has been reused or corrupted, the lookup or subsequent `module_put()` may fault or operate on an invalid pointer. This is category A in the cleanup distinction: an ordinary stale cleanup dereference. It is not category B repeated lifetime corruption because the second operation does not perform another put on the exact freed DMA object. The primitive is CLASS_B because a real post-lifetime object access is confirmed. It is not CLASS_A because controlled reclaim, directed corruption, callback influence, refcount takeover, arbitrary read or write, and privilege escalation are not established. The patch-supported practical consequence is KASAN detection and potential kernel crash or DoS. More extensive corruption through allocator reuse is theoretically possible but lacks the attacker control required for scoring. ImportantCandidate is therefore NO, while manual review remains recommended because `module_put()` consumes a value obtained through the stale object. AutoDowngradeAllowed is YES because this is presently a constrained release-path UAF without a concrete repeated lifetime mutation or independently useful exploitation primitive. Likely operational severity is Moderate or borderline Moderate rather than Important. 5. One-sentence report phrase A final DMA device reference can be dropped before its channel owner is read, causing a confirmed release-path use-after-free and a possible kernel crash when the stale owner value is consumed by module_put(). 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review the affected DMA provider and callers to determine whether a below-host-admin actor can repeatedly force the final release and influence reuse before `dma_chan_to_owner()`, but the supplied evidence does not currently establish an Important-grade exploitation primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() [ Upstream Commit: b92c502595336a3cc5bb7a060170891366745a5d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b92c502595336a3cc5bb7a060170891366745a5d Changed files: drivers/dma/dmaengine.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=b92c502595336a3cc5bb7a060170891366745a5d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98343 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98343 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:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: unknown Paranoid ActionableScore: 4 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).