From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98512][IMPORTANT] drm/nouveau: RCU-free the scheduler-containing nouveau_sched Date: Sat, 24 Oct 2026 07:25:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98512 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 40edf5eefc3fd94592a91d6eb074d4fc6f606c75 List-Id: CVE: CVE-2026-98512 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: drm/nouveau: RCU-free the scheduler-containing nouveau_sched Commit: 40edf5eefc3fd94592a91d6eb074d4fc6f606c75 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40edf5eefc3fd94592a91d6eb074d4fc6f606c75 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98512 Analysis date: Sat, 24 Oct 2026 07:25:00 -0400 ActionableScore: 6 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An unprivileged render-node client can retain an exported fence past Nouveau scheduler destruction and later trigger a userspace-facing read from the freed scheduler through `SYNC_IOC_FILE_INFO`. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98512 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98512 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: IMPORTANT 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-2026-98512 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98512 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H';*CWE-416;*CWE-664;*CWE-672;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '7.1';DESCR 'A lifetime error in Nouveau frees nouveau_sched while an exported and already signalled scheduler fence can still reference the embedded drm_gpu_scheduler. An unprivileged process with access to the Nouveau DRM render node can retain the fence through drm_syncobj or sync_file and later call SYNC_IOC_FILE_INFO, causing get_timeline_name to read fence sched name from freed slab memory. For the CVSS the PR:L value is selected because local user execution and access to the DRM device are required, while administrative privileges are not normally required. The demonstrated primitive is a UAF read that can cause a limited stale heap disclosure and may crash a protected kernel. No write primitive is shown, so integrity impact remains none. The paranoid score allows high confidentiality and availability impact if repeated slab reuse exposes sensitive kernel data or the invalid access causes a host wide kernel failure. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 5.7 and ActionableScore 4 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 IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) MAYBE DANGER UAF HARDWARE LINUS MEMORY INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 6. * Conservative score: 6; no floor or cap changed the result. * Raw paranoid score: 6. * Paranoid score: 6; no additional speculative reuse, disclosure, or crash points. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Real UAF: `nouveau_sched_destroy()` frees the scheduler while an exported fence retains `fence->sched`; `get_timeline_name()` later dereferences it. * +1 Concrete RCU referenced-object lifetime mismatch: the fence remains legitimately accessible, but its referenced scheduler storage is freed before the required RCU grace period. `kfree_rcu()` directly repairs this invariant. * +1 Local unprivileged trigger: supplied call-path evidence grounds Nouveau render-node access and `SYNC_IOC_FILE_INFO` without host-administrator privilege. * +1 Confidentiality plausible: timeline-name retrieval reads the stale scheduler name for userspace-facing fence information, supporting limited stale slab disclosure. * +1 Reliable kernel crash/strong DoS plausible: the confirmed slab UAF read can fault or become fatal under KASAN/panic policy. * No separate availability point: it would duplicate the same UAF fault. * No structured-reuse, controlled-reclaim, arbitrary-write, integrity, callback-control, or LPE bonus is awarded. * No race penalty: a narrow, attacker-uncontrollable timing race is not shown. * B4-PENDING does not apply; no authorization decision changes from DENY to ALLOW. 3. Reachability analysis A local process with access to the Nouveau DRM render node can retain an exported, signalled fence through syncobj/sync_file and invoke `SYNC_IOC_FILE_INFO`. This is positively grounded below host-admin and does not require UID 0 or a namespace capability. Device-node access remains a deployment prerequisite, but no unusual hardware or privileged setup penalty is justified. The destruction/use ordering is a lifetime sequence, not a demonstrated hard race. 4. Primitive and severity reading This is a CLASS_B active structured-object UAF read, not fixed stale DMA storage. The stale operation reads scheduler state after destruction; there is no repeated release/refcount mutation. The patch proves the RCU lifetime defect and userspace-facing stale read, but not controlled reclaim, arbitrary disclosure contents, write corruption, or privilege escalation. ImportantCandidate is YES because a concrete below-host-admin RCU UAF reaches a userspace-visible consumer and its disclosure/crash extent depends on slab reuse. Auto-downgrade is disallowed pending review of name-copy bounds, allocator reuse, and teardown reachability. 5. One-sentence report phrase An unprivileged render-node client can retain an exported fence past Nouveau scheduler destruction and later trigger a userspace-facing read from the freed scheduler through `SYNC_IOC_FILE_INFO`. 6. Manual review advice MANUAL CHECK REQUIRED Confirm the exact copied name length, slab-reuse disclosure extent, and production render-node permissions. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm/nouveau: RCU-free the scheduler-containing nouveau_sched Commit: 40edf5eefc3fd94592a91d6eb074d4fc6f606c75 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40edf5eefc3fd94592a91d6eb074d4fc6f606c75 Commit description: struct nouveau_sched embeds a struct drm_gpu_scheduler (base). nouveau_sched_destroy() calls nouveau_sched_fini() (which does drm_sched_fini(&sched->base)) and then frees the object with plain kfree(sched). drm_sched_fence_get_timeline_name() returns fence->sched->name, and the scheduler fence keeps a .release callback so it is not ops-detached on signalling. A finished fence exported to userspace via drm_syncobj / sync_file therefore keeps pointing at &sched->base after nouveau_sched_destroy(), and a later get_timeline_name() -- reachable unprivileged through SYNC_IOC_FILE_INFO -- dereferences freed memory (KASAN slab-use-after-free read). Per the dma-fence lifetime contract the exporter must keep the data backing a signalled fence alive for an RCU grace period. Free the scheduler-containing object with kfree_rcu() instead of kfree(). Fixes: 5f03a50 ("drm/nouveau: implement 1:1 scheduler - entity relationship") Cc: stable@vger.kernel.org Signed-off-by: Jonghyuk Kim(MalHyuk) Reviewed-by: Lyude Paul Signed-off-by: Lyude Paul Link: https://patch.msgid.link/20260902012717.880724-1-malhyuk97@gmail.com Signed-off-by: Greg Kroah-Hartman Changed files: drivers/gpu/drm/nouveau/nouveau_sched.c drivers/gpu/drm/nouveau/nouveau_sched.h 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=40edf5eefc3fd94592a91d6eb074d4fc6f606c75 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98512 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98512 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:L/PR:L/UI:N/S:U/C:L/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H The Best / paranoid CVSS score: 7.1 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: 6 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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).