[CVE-2026-68271][MODERATE REGULAR] drm/nouveau: fix reversed error cleanup order in ucopy functions

[CVE-2026-68271][MODERATE REGULAR] drm/nouveau: fix reversed error cleanup order in ucopy functions

[AL-KERNEL]

CVE: CVE-2026-68271
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/nouveau: fix reversed error cleanup order in ucopy functions
Commit: 2473ac314387a5def7244eb6d6a345934ed140bf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2473ac314387a5def7244eb6d6a345934ed140bf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68271
Analysis date: Mon, 10 Aug 2026 19:08:12 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A local user with access to the Nouveau DRM device can trigger reversed ucopy cleanup ordering so an ERR_PTR is passed to u_free()/kvfree(), causing a kernel oops and denial of service without evidence of a controllable privilege escalation primitive.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-68271 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68271

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-68271	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-763;**CWE-476;CWE-703;BEST CVSS score: '5.5';DESCR 'A local NULL or invalid pointer dereference can occur in Nouveau ucopy error handling because cleanup labels free resources in allocation order instead of reverse allocation order. If u_memcpya() fails while copying in_sync.s, args in_sync s can keep an ERR_PTR value and the fallthrough cleanup path can pass it to u_free and then kvfree, causing a kernel oops. For the CVSS the PR:L is used because reliable triggering requires local access to the Nouveau DRM user API or render device, but it does not require full administrator privileges on systems where such device access is delegated to users. The issue is not network reachable and is triggered through local GPU ioctl style interfaces. Impact is denial of service via kernel crash. No concrete UAF, OOB write, information leak, or arbitrary write primitive is visible from the patch context, so confidentiality and integrity are not scored.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 4)  SKIP CVE-2026-68271 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: b88baab828713ce0b49b185444b2ee83bed373a8 YES  NO NO unknown 	MAYBE	INIT LEAK UAF HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  The affected Nouveau VM_BIND and exec ucopy paths are reachable through local DRM/Nouveau user API paths when a local user has access to the relevant DRM device or render node.

* Weak or indirect corruption candidate: +1
  The bug passes an ERR_PTR value into u_free()/kvfree() due to reversed cleanup ordering. This is an invalid pointer/free-path misuse, but the patch does not show UAF reclaim, object replacement, OOB write, arbitrary write, or type confusion.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly states that kvfree() may dereference the ERR_PTR and cause a kernel oops.

Paranoid additional signal:

* Availability impact realistic: +1
  If the ioctl path can be triggered reliably by forcing u_memcpya() failure, the issue can become a practical local kernel crash condition on affected Nouveau systems.

Not awarded:

* No privilege escalation plausible: +0
  No concrete reclaim, write primitive, stale callback, refcount abuse, or attacker-controlled object confusion is shown.

* No generic strong memory corruption: +0
  The evidence supports invalid pointer dereference/free-path misuse, not a controllable memory corruption primitive.

* No remote reachable: +0
  This is a local DRM ioctl style path, not a network path.

* No high-control API bonus: +0
  DRM ioctls are rich object APIs, but the patch does not show attacker control over allocator reuse, callback targets, DMA mappings, refcounts, or page ownership.

## 3. Reachability analysis

A local user with access to the Nouveau DRM device interface can plausibly trigger the affected ucopy error paths by causing u_memcpya() failure during VM_BIND or exec argument copying. This does not normally require full administrator privileges on systems where GPU render node access is delegated to desktop or compute users. Containers may matter if the DRM device is passed through or exposed, but without device access the bug is not reachable. The issue is hardware and driver dependent because it requires Nouveau and the affected VM_BIND uAPI path, so exposure is narrower than core kernel APIs.

Call-site confidence: high. The provided patch includes the affected cleanup labels and the commit message explains the concrete failure path into u_free()/kvfree().

## 4. Severity interpretation

This behaves like a local actionable Moderate DoS rather than an Important vulnerability. The realistic impact is kernel oops or crash through a local GPU driver interface. Theoretical memory-corruption concern is limited because an ERR_PTR is passed into a free path, but the supplied patch does not support a practical LPE primitive. Manual review is still useful because the path is user reachable and involves invalid pointer handling in a kernel driver cleanup path.

## 5. One-sentence report phrase

A local user with access to the Nouveau DRM device can trigger reversed ucopy cleanup ordering so an ERR_PTR is passed to u_free()/kvfree(), causing a kernel oops and denial of service without evidence of a controllable privilege escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: user-reachable kernel driver crash path with invalid pointer/free-path misuse, but no demonstrated UAF reclaim, arbitrary write, information leak, or privilege escalation primitive.

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

Patch: drm/nouveau: fix reversed error cleanup order in ucopy functions
Commit: 2473ac314387a5def7244eb6d6a345934ed140bf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2473ac314387a5def7244eb6d6a345934ed140bf

Commit description:

nouveau_uvmm_vm_bind_ucopy() and nouveau_exec_ucopy() place their error
cleanup labels in allocation order rather than reverse allocation order.
On a u_memcpya() failure for in_sync.s, the goto to err_free_ops (or
err_free_pushs) frees the first allocation and then falls through to
err_free_ins, which calls u_free() on args->in_sync.s.

Since args->in_sync.s still holds the ERR_PTR returned by the failed
u_memcpya(), and ERR_PTR values are not caught by ZERO_OR_NULL_PTR(),
kvfree() proceeds to dereference it, which can result in a kernel oops.
A failure for out_sync.s instead jumps to err_free_ins and skips freeing
the first allocation, leading to a memory leak.

Fix by swapping the cleanup label order so resources are freed in the
correct reverse allocation sequence.

Fixes: b88baab ("drm/nouveau: implement new VM_BIND uAPI")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB7881484D91A6F80271415F71AF1A2@SYBPR01MB7881.ausprd01.prod.outlook.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_exec.c
  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=2473ac314387a5def7244eb6d6a345934ed140bf

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

The original Linux kernel CVE announcement for CVE-2026-68271 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68271

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: 3
  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).