From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99095][MODERATE 7.0] drm/vc4: drain the hangcheck timer and works on V3D unbind Date: Mon, 26 Oct 2026 22:25:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99095 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 17c5fa371de2d5508755cd4cd227cc8e2bb99240 List-Id: CVE: CVE-2026-99095 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: drm/vc4: drain the hangcheck timer and works on V3D unbind Commit: 17c5fa371de2d5508755cd4cd227cc8e2bb99240 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=17c5fa371de2d5508755cd4cd227cc8e2bb99240 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99095 Analysis date: Mon, 26 Oct 2026 22:25:12 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: VC4 teardown fails to drain embedded timer and work callbacks, permitting a compound-trigger post-free access and kernel crash without demonstrated controlled reuse or write leverage. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99095 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99095 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 7.0 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-2026-99095 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99095 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both 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-362;**CWE-476;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A teardown race in the VC4 V3D driver can leave the hangcheck timer, reset_work, or job_done_work active after vc4_v3d_unbind removes the interrupt handler and clears vc4 v3d. The timer can dereference the cleared V3D pointer, while callbacks that execute after vc4_dev is freed access embedded timer and work objects through released kernel memory. This establishes a use after free dereference and kernel crash risk, although the available change does not demonstrate a controlled arbitrary write. For the CVSS the PR:L paranoid value reflects a local render node user who can submit jobs and keep callbacks pending while an independently initiated device unbind creates the required teardown window. The issue is local, race dependent, and not directly network reachable. Impact is at least a local denial of service and the use after free may permit wider confidentiality or integrity impact if the released object can be reclaimed in a useful layout. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 3 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE INIT SIMPLEFIX LEAK DMAorINTERRUPT TIMER HARDWARE LINUS INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3. * Conservative score: 3; no floor or cap applied. * Raw paranoid score: 3. * Paranoid score: 3; stronger reuse or write leverage is not evidenced. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +2 Real UAF/lifetime violation: timer and work callbacks can execute after the embedding `vc4_dev` has been freed. * +1 Reliable kernel crash concern: the timer can dereference cleared `vc4->v3d`, and post-free callbacks can fault through released storage. * No race penalty: teardown ordering is involved, but the evidence does not establish a narrow or difficult-to-repeat race. * No privilege penalty: complete-trigger privilege is unresolved rather than proven host-admin-only. * No structured-stale leverage: no controlled reclaim, attacker-shaped replacement, callback pointer control, directed write, or distinct post-reuse field consumption is shown. * No confidentiality, integrity, arbitrary-write, LPE, remote-reachability, or extra availability point. * No UAF floor: this is teardown-associated fixed driver context/embedded callback storage with crash as the supported outcome. * No repeated-release signal: flushing `job_done_work` releases pending jobs, but the evidence does not show two lifetime mutations on the exact same dangling reference. 3. Reachability analysis A render-node user may submit jobs and arm pending callbacks, but the necessary V3D unbind is independently initiated. The evidence does not show that the same below-host-admin actor can induce unbind, making this a compound and incompletely established trigger. Render-device access is permission-mediated, not a namespace capability path. VC4 hardware is required, but it is not sufficiently rare to justify a hardware penalty. 4. Primitive and severity reading The exact primitive is asynchronous access through timer/work objects embedded in a freed `vc4_dev`, plus a pre-free NULL-register dereference after `vc4->v3d` is cleared. This is a constrained teardown UAF, CLASS_B, with plausible kernel DoS. Useful corruption after excluding the crash is unproven. It is therefore not an Important candidate, and automatic downgrade remains permissible, though manual validation of render-node reachability and teardown control is advisable. No authorization decision is changed, so B4-PENDING does not apply. 5. One-sentence report phrase VC4 teardown fails to drain embedded timer and work callbacks, permitting a compound-trigger post-free access and kernel crash without demonstrated controlled reuse or write leverage. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether an unprivileged render-node client can reliably overlap submitted work with an attacker-inducible unbind path. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm/vc4: drain the hangcheck timer and works on V3D unbind Commit: 17c5fa371de2d5508755cd4cd227cc8e2bb99240 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=17c5fa371de2d5508755cd4cd227cc8e2bb99240 Commit description: Nothing stops the hangcheck timer that submitted jobs arm, or the job_done_work that the render-done interrupt queues, at teardown: vc4_irq_disable() cancels only overflow_mem_work, and vc4_gem_destroy() runs from the drm-managed release, after vc4_v3d_unbind() has already uninstalled the V3D interrupt and cleared vc4->v3d. A timer still armed by then reads V3D registers through the NULL vc4->v3d pointer, and the late callbacks run on the vc4_dev embedding them after it has been freed. Drain them in vc4_v3d_unbind(): shut the timer down and cancel reset_work before the interrupt is taken down, because its vc4_irq_reset() re-enables it, then flush job_done_work so that completions queued at teardown still release their jobs. This issue was found by an in-house static analysis tool. Fixes: d5b1a78 ("drm/vc4: Add support for drawing 3D frames.") Cc: stable@vger.kernel.org # 6.2+ Assisted-by: Codex:gpt-5.6 Co-developed-by: Song Li Signed-off-by: Song Li Signed-off-by: Fan Wu Link: https://patch.msgid.link/20260915095103.156007-1-fanwu01@zju.edu.cn Reviewed-by: Maíra Canal Signed-off-by: Maíra Canal Signed-off-by: Greg Kroah-Hartman Changed files: drivers/gpu/drm/vc4/vc4_v3d.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=17c5fa371de2d5508755cd4cd227cc8e2bb99240 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99095 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99095 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:L/I:L/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: 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).