[CVE-2026-89996][MODERATE REGULAR] dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-89996
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds [ Upstream
Commit: 69d57dbadb27ffd5eef34fd184bab145500cdabc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69d57dbadb27ffd5eef34fd184bab145500cdabc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89996
Analysis date: Wed, 16 Sep 2026 11:53:35 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89996 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89996

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-89996	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89996 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-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A dma heap allocation ioctl could publish a dma buf fd into the caller fd table before the final copy_to_user returned the fd number to userspace. If copy_to_user failed, the caller received an error but the fd and the underlying dma buf reference could remain visible to other threads in the same process and leak until process exit. For the CVSS the PR:L is used because a local process needs access to /dev/dma_heap and must invoke DMA_HEAP_IOCTL_ALLOC. The issue is not network reachable and does not provide a direct information leak, arbitrary write, or privilege escalation primitive. Impact is denial of service through local resource exhaustion, mainly fd table pressure and dma buf heap memory consumption. The base score uses A:L because a single failed ioctl is only a limited leak. The paranoid score uses A:H because repeated failed allocations can realistically exhaust local resources on systems where dma heap access is available to untrusted processes.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 3)	YES	LEAK DMAorINTERRUPT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 Concrete persistent kernel resource/reference leak. The fd is installed before the final copy_to_user() succeeds, and on copy_to_user() failure userspace does not learn the fd while the fd and underlying dma-buf reference remain alive until process exit.
* +1 Local userspace reachable trigger. The commit explicitly states that the copy_to_user() failure is easily reachable from userspace by changing page protection between copy_from_user() and copy_to_user().

Paranoid additional signal:

* +1 Sustained local resource exhaustion concern. Repeated failed DMA_HEAP_IOCTL_ALLOC calls can accumulate leaked dma-buf fds and backing heap resources where /dev/dma_heap access is available.

Non-awarded signals:

* RealUAF not awarded. This is a leaked published fd/reference, not use after free.
* Concrete repeated release/refcount not awarded. There is no first release followed by a second lifetime mutation on the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded. The bug does not show information disclosure, protected object access, or unauthorized modification.
* Reliable kernel crash not awarded. The demonstrated effect is resource leakage, not immediate panic or Oops.
* Extra availability point not awarded beyond the paranoid sustained exhaustion signal.
* Remote reachability not established.
* ImportantCandidate not set because the issue is a local resource leak without memory corruption, ownership bypass, authorization bypass, or LPE evidence.

3. Reachability analysis

The trigger is local userspace with access to a dma-heap device node such as /dev/dma_heap/name. The supplied commit states that the failure is easily reachable by placing struct dma_heap_allocation_data in memory whose protection is changed before the trailing copy_to_user().

Host administrator privileges are not established as required for the vulnerable ioctl itself, so HostAdminRequired=NO. The practical attacker still needs permission to open the relevant dma-heap device node, which is deployment dependent.

No namespace-scoped capability is involved in the provided evidence, so NamespaceScopedPrivilege=NO. There is no network path. There is no race requirement in the security-relevant sense. The mprotect timing is a controlled local sequence, not a hard kernel race.

There may be prior system configuration deciding which dma heaps exist and what device permissions apply, but the vulnerability is in the ioctl allocation path once the device is accessible. No special rare hardware requirement is established beyond systems exposing dma-buf heaps.

4. Primitive and severity interpretation

The exact primitive is a resource/reference leak caused by publishing an fd with fd_install() before all fallible ioctl work has completed. If copy_to_user() fails afterward, the kernel has already made the fd visible to other threads, but the calling thread receives an error and may never know the fd number.

This is not active structured UAF and not fixed stale storage. It is an ownership/lifetime ordering bug for an fd and dma-buf reference.

There is no concrete repeated release/refcount operation. The first operation does not free an object and leave the same dangling reference for a later second put. Instead, the problem is that cleanup cannot safely close the fd after publication because another thread may have duplicated, transferred, closed, or caused reuse of that fd number.

PrimitiveClass=CLASS_C because the demonstrated behavior is local DoS/resource exhaustion without an independently useful corruption primitive. The demonstrated consequence is leaked fd and dma-buf resources until process exit. The speculative consequence is broader local resource exhaustion after repeated abuse. There is no patch-supported path to privilege escalation, arbitrary kernel read/write, or security-boundary bypass.

ImportantCandidate=NO because the issue remains a resource leak with no memory corruption or boundary bypass. AutoDowngradeAllowed=YES because no unresolved Important-grade primitive would be lost by treating this as ordinary Moderate/Low-like operational risk.

5. One-sentence report phrase

DMA_HEAP_IOCTL_ALLOC could publish a dma-buf fd before copy_to_user() succeeded, allowing a local userspace process with dma-heap access to leak dma-buf fds and references on failure and potentially cause resource-exhaustion DoS.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a local persistent resource/reference leak without UAF, repeated refcount mutation, controlled corruption, authorization bypass, information disclosure, or privilege escalation evidence.

7. Call-site confidence

Call-site confidence: high

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

Patch: dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds [ Upstream
Commit: 69d57dbadb27ffd5eef34fd184bab145500cdabc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69d57dbadb27ffd5eef34fd184bab145500cdabc

Changed files:
  drivers/dma-buf/dma-buf.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=69d57dbadb27ffd5eef34fd184bab145500cdabc

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

The original Linux kernel CVE announcement for CVE-2026-89996 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89996

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:N/I:N/A:L
  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: 2
  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).