[CVE-2026-89802][MODERATE REGULAR] drm/nouveau/uvmm: fix NULL deref unwinding an OP_MAP_SPARSE op

[CVE-2026-89802][MODERATE REGULAR] drm/nouveau/uvmm: fix NULL deref unwinding an OP_MAP_SPARSE op

[AL-KERNEL]

CVE: CVE-2026-89802
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/nouveau/uvmm: fix NULL deref unwinding an OP_MAP_SPARSE op
Commit: 3bf493cf7ed0c2b3df728977a257e0d99b4db1c6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3bf493cf7ed0c2b3df728977a257e0d99b4db1c6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89802
Analysis date: Wed, 16 Sep 2026 08:25:07 -0400
ActionableScore: 3
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-2026-89802 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89802

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-2026-89802	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89802 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;CWE-703;BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the drm nouveau VM_BIND reverse unwind path occurs because an OP_MAP_SPARSE operation can leave op ops as NULL after successful sparse map processing. If a later operation in the same bind job fails, the unwind loop can call drm_gpuva_ops_free() with this NULL value and crash the kernel. For the CVSS the PR:L is chosen because triggering requires local access to a DRM render node fd, but root privileges are not normally required when NOUVEAU_VM_BIND is exposed through DRM_RENDER_ALLOW. The issue is not network reachable and is triggered through the local GPU driver ioctl path. Impact is denial of service via kernel crash. No confidentiality or integrity impact is assigned because the supported primitive is a NULL pointer dereference rather than UAF, OOB write, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	INIT SIMPLEFIX HARDWARE LINUS 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +1 Local below-host-admin trigger. The supplied context states that the path is reachable by any render-node fd holder because NOUVEAU_VM_BIND is DRM_RENDER_ALLOW.
* +1 Reliable kernel crash / strong DoS. drm_gpuva_ops_free() dereferences ops immediately, and op->ops can be NULL, causing an Oops.
* +1 Local high-control ioctl request sequencing. The attacker controls a VM_BIND job containing OP_MAP_SPARSE followed by a later failing operation, which controls the error-unwind state needed to reach the NULL dereference.

Non-awarded signals:

* +0 Real UAF. No freed object or stale post-lifetime reference is established.
* +0 Strong corruption. No OOB write, arbitrary write, controlled reclaim, type confusion, or refcount mutation is established.
* +0 Structured stale-object leverage. The primitive is a NULL argument passed into a helper, not stale structured-object reuse.
* +0 Confidentiality and integrity. No disclosure path or unauthorized write is supported.
* +0 Extra availability. The same kernel crash is already counted once.
* +0 Remote reachability. The trigger is a local DRM ioctl path, not packet or network input.
* No negative privilege penalty. Host-admin-equivalent privilege is not required according to the supplied render-node evidence.
* No race penalty. This is an ordered error-unwind sequence, not a timing race.

3. Reachability analysis

The evaluated attacker is a local process that can open a Nouveau DRM render node and issue the NOUVEAU_VM_BIND ioctl. The supplied context explicitly says the ioctl is exposed through DRM_RENDER_ALLOW, so root or host-admin-equivalent privilege is not required for the vulnerable operation.

This is not a DRM master or display-control path. It is a render-node GPU VM_BIND path. Namespace-scoped privilege is not relevant and no network trigger is established. No prior privileged setup is shown beyond having a Nouveau device and render node available. Special hardware is required in the ordinary sense that Nouveau-supported NVIDIA GPU hardware must be present, but this is not treated as rare or physical-only enough for a scoring penalty. No timing race is needed.

4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference in the VM_BIND reverse-unwind path. OP_MAP_SPARSE can leave op->ops as NULL after successful sparse-map processing. If a later operation in the same job fails, the reverse unwind loop revisits the sparse operation and calls drm_gpuva_ops_free() on NULL.

This is not an active structured UAF and not fixed stale storage. It is cleanup/error-unwind invalid-state behavior ending in an immediate NULL dereference. There is no concrete repeated release or refcount operation on a dangling object. There is no evidence that the first operation can free an object and that the same reference later receives a second lifetime mutation.

PrimitiveClass is CLASS_C because the demonstrated behavior is crash/DoS without an independently useful corruption primitive. The demonstrated consequence is a local kernel crash. Stronger consequences such as privilege escalation are speculative and not supported by the patch mechanics. ImportantCandidate is NO because no Class A or strong Class B primitive is established. AutoDowngradeAllowed is YES because the issue is crash-only Class C, although manual review is still recommended due to below-host-admin reachability through a DRM render ioctl.

Likely operational severity is a local actionable DoS on affected Nouveau systems, but not an Important-class corruption candidate based on the supplied evidence.

5. One-sentence report phrase

A local render-node fd holder can trigger a NULL pointer dereference in the Nouveau VM_BIND unwind path by submitting an OP_MAP_SPARSE operation followed by a failing operation, causing a kernel crash without evidence of UAF, memory corruption, information disclosure, or privilege escalation.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is reachable below host-admin through a DRM render ioctl and can crash the kernel, but the supported primitive is only a NULL pointer dereference with no UAF, refcount corruption, arbitrary write, or demonstrated privilege-escalation path.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: drm/nouveau/uvmm: fix NULL deref unwinding an OP_MAP_SPARSE op
Commit: 3bf493cf7ed0c2b3df728977a257e0d99b4db1c6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3bf493cf7ed0c2b3df728977a257e0d99b4db1c6

Commit description:

Each bind_job_op is zeroed by kzalloc_obj() in bind_job_op_from_uop(),
and the OP_MAP_SPARSE case in nouveau_uvmm_bind_job_submit() only creates
a region, so op->ops stays NULL for a successfully processed sparse map.

If a later op in the same job fails, the reverse unwind loop revisits that
op and calls drm_gpuva_ops_free(&uvmm->base, op->ops) unconditionally.
drm_gpuva_ops_free() dereferences its argument right away
(list_for_each_entry_safe on &ops->list), so a NULL op->ops oopses. The
path is reachable by any render-node fd holder, since NOUVEAU_VM_BIND is
DRM_RENDER_ALLOW.

Guard the free with IS_ERR_OR_NULL(), as nouveau_uvmm_bind_job_cleanup()
already does for the identical free.

Fixes: b88baab ("drm/nouveau: implement new VM_BIND uAPI")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Assisted-by: Claude:claude-opus-5
Cc: stable@vger.kernel.org
Signed-off-by: Zhenhao Wan <whi4ed0g@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260811-nouveau-uvmm-vmbind-fixes-v2-1-aaee4b395d04@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/nouveau/nouveau_uvmm.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=3bf493cf7ed0c2b3df728977a257e0d99b4db1c6

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89802 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89802

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 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).