[CVE-2026-72476][MODERATE 7.0] dmaengine: Fix possible use after free [ Upstream

[CVE-2026-72476][MODERATE 7.0] dmaengine: Fix possible use after free [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72476
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dmaengine: Fix possible use after free [ Upstream
Commit: 444f96066937f3fdf0e79b53289cff223c7d638b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=444f96066937f3fdf0e79b53289cff223c7d638b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72476
Analysis date: Sat, 15 Aug 2026 19:35:00 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A possible use-after-free in `dma_release_channel()` can occur when `dma_chan_put()` drops the last DMA device reference before `privatecnt` cleanup, allowing a local DMA provider teardown path to crash the kernel and requiring manual review for possible memory corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72476 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72476

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 7.0
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
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CVE-2026-72476	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A possible use-after-free exists in dma_release_channel() because dma_chan_put() can drop the last reference to the DMA device when the provider is already gone, while the code still updates privatecnt through the stale chan device pointer afterward. This is a local lifecycle race around DMA channel release and provider teardown, not a network reachable issue. For the CVSS the PR:L is used in the paranoid score because a local user or service with access to a DMA client release path or delegated device management might be able to trigger the release during provider teardown, although direct provider removal is typically administrative. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption from use of a freed device object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	UAF DMAorINTERRUPT HARDWARE LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

### Conservative score: 3

* +2 Memory corruption, strong corruption primitive: explicit possible UAF. `dma_chan_put()` can drop the last reference to the DMA device, after which `chan->device->privatecnt` and `chan->device->cap_mask` are still accessed.
* +1 Real lifetime corruption: this is a reference lifetime ordering bug where a device object may be freed before the final private capability cleanup.
* +1 Reliable kernel crash / strong DoS: if the provider is already gone and the final reference is dropped, the stale device access can plausibly crash the kernel.
* +1 Privileged kernel/device-management memory corruption path: the bug is in DMA engine channel release and provider teardown, a privileged device-management context.
* -2 Requires admin/root/CAP-like control in typical deployments: reliable triggering usually requires driver unload, unbind, hotplug, provider removal, or privileged control over a DMA client/provider lifecycle.

Conservative total: 3

### Paranoid score: 5

* +2 Memory corruption, strong corruption primitive: UAF with subsequent write-like metadata update through `--privatecnt` and possible `dma_cap_clear()`.
* +1 Real lifetime corruption: stale pointer after final reference release.
* +1 Reliable kernel crash / strong DoS: kernel crash is a realistic outcome.
* +1 Privileged kernel/device-management memory corruption path: DMA/device lifetime code is high-value kernel infrastructure.
* +1 Weak LPE concern: there is no demonstrated reclaim or controlled replacement, but write-after-free into a freed device object is enough to require manual review.
* -1 Corruption primitive constrained: the observed writes are metadata-oriented and not shown to be attacker-controlled arbitrary writes.

Paranoid total: 5

Call-site confidence: medium. The vulnerable function and direct lifetime ordering are visible, but broader DMA client call paths are not included in the input.

## 3. Reachability analysis

The likely trigger is local and tied to DMA channel release while the DMA provider has already gone away. In normal deployments this usually requires administrative device-management actions such as driver unload, device unbind, hotplug, or privileged control over a DMA client lifecycle.

Namespaces and containers do not generally make DMA provider teardown available to ordinary unprivileged users. A reduced-privilege service, container root with delegated device access, or a driver-specific userspace interface could lower the practical privilege requirement, but that is not proven by the patch.

The path is not network reachable. DMAengine is common kernel infrastructure, but exploitation depends on a specific DMA provider/client lifecycle condition.

## 4. Severity interpretation

This is not an ordinary cleanup bug because the patch fixes an explicit possible use-after-free in core DMA lifetime handling. Realistic impact is most clearly local kernel crash or host instability during provider teardown.

Privilege escalation is not demonstrated. However, because the stale object is accessed after a possible final put and because freed kernel memory may be reused, the issue should be treated as Actionable Moderate at minimum and manually reviewed for stronger memory corruption impact.

## 5. One-sentence report phrase

A possible use-after-free in `dma_release_channel()` can occur when `dma_chan_put()` drops the last DMA device reference before `privatecnt` cleanup, allowing a local DMA provider teardown path to crash the kernel and requiring manual review for possible memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes a UAF in DMA/device lifetime management, and the stale pointer is used after a final reference may be released. Practical LPE is not proven, but memory corruption class and privileged device lifecycle context make auto-close unsafe.

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

Patch: dmaengine: Fix possible use after free [ Upstream
Commit: 444f96066937f3fdf0e79b53289cff223c7d638b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=444f96066937f3fdf0e79b53289cff223c7d638b

Changed files:
  drivers/dma/dmaengine.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=444f96066937f3fdf0e79b53289cff223c7d638b

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

The original Linux kernel CVE announcement for CVE-2026-72476 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72476

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 5

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 7.0

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).