[CVE-2026-98512][IMPORTANT] drm/nouveau: RCU-free the scheduler-containing nouveau_sched

[CVE-2026-98512][IMPORTANT] drm/nouveau: RCU-free the scheduler-containing nouveau_sched

[AL-KERNEL]

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`.

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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.

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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

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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) <malhyuk97@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260902012717.880724-1-malhyuk97@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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).