[CVE-2026-72149][LOW] dmaengine: tegra: Fix burst size calculation

[CVE-2026-72149][LOW] dmaengine: tegra: Fix burst size calculation

[AL-KERNEL]

CVE: CVE-2026-72149
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dmaengine: tegra: Fix burst size calculation
Commit: 735951baa311c66353405dcac39375dd66441db0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=735951baa311c66353405dcac39375dd66441db0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72149
Analysis date: Sat, 15 Aug 2026 07:38:35 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like, not an Important candidate
Manual review required: YES

Summary:
The Tegra GPC DMA driver could select a burst size that does not divide the requested transfer length, causing partial-burst DMA hangs for clients such as PL011 UART TX DMA and resulting in local device-level denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-72149 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72149

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: LOW
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-2026-72149	LOW	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-682;CWE-754;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The Tegra GPC DMA driver could program a burst size that does not evenly divide the requested transfer length. When the final transfer fragment becomes a partial burst, the hardware may hang instead of completing the DMA operation. This was observed with PL011 UART TX DMA where user supplied or driver supplied transmit lengths can be arbitrary. For the CVSS the PR:L is used because reliable triggering generally requires local access to a DMA backed client device such as a UART tty or another local interface using this DMA engine. The issue is not network reachable by itself and does not show evidence of memory corruption, information disclosure, or privilege escalation. Impact is denial of service through a stuck DMA transfer, usually limited to the affected device path but potentially higher if the DMA controller or dependent driver cannot recover cleanly.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, not an Important candidate (with actual score 2)	YES	SIMPLEFIX DMAorINTERRUPT HARDWARE LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like, not an Important candidate**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user or process may be able to submit arbitrary-length TX data through a DMA-backed client such as PL011 UART, depending on device permissions.

* Reliable device-level DoS: +1
  The described failure is a DMA hang when the transfer length is not divisible by the programmed burst size. This is a realistic availability issue for the affected DMA channel or client device.

* Availability impact realistic: +1 only in paranoid score
  Counted only for the paranoid score because a stuck DMA channel may require driver reset or affect dependent device operation. It is not clearly system-wide from the patch.

Subtracting signals:

* Rare and hardware-specific path: -1
  This requires Tegra GPC DMA hardware and a client using DMA transfers with incompatible lengths. It is not a broad kernel path.

Not triggered:

* No remote reachability.
* No firmware-mediated attacker influence shown.
* No UAF, double free, OOB write, type confusion, arbitrary write, page-cache corruption, or lifetime corruption.
* No plausible privilege escalation primitive.
* No confidentiality or integrity impact supported by the patch.

Call-site confidence: medium. The patch only shows the helper change, but the commit explicitly states the observed PL011 UART TX DMA call path.

## 3. Reachability analysis

The bug is locally reachable through DMA clients that can request transfers of arbitrary length. The clearest described case is PL011 UART TX DMA. In practice, triggering depends on whether an untrusted user can access the relevant tty or another DMA-backed device path.

Namespaces and containers do not generally make this broadly reachable unless the affected device node is delegated into the container. The path is hardware-specific to Tegra GPC DMA and is not network-triggerable by itself. Realistic exploitation is a local device DoS, not host compromise.

## 4. Severity interpretation

This behaves like a Low or ordinary Moderate availability bug. The failure mode is a DMA transfer hang caused by unsupported partial bursts. There is no evidence of memory corruption, data disclosure, privilege escalation, or cross-boundary policy bypass.

The paranoid score only raises availability from limited device impact to stronger DoS in case recovery requires reset or affects a critical serial path. It still does not become Actionable Moderate or Important.

## 5. One-sentence report phrase

The Tegra GPC DMA driver could select a burst size that does not divide the requested transfer length, causing partial-burst DMA hangs for clients such as PL011 UART TX DMA and resulting in local device-level denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED because this is a hardware-specific DMA hang with no supported memory corruption, privilege escalation, confidentiality impact, integrity impact, or network exposure.

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

Patch: dmaengine: tegra: Fix burst size calculation
Commit: 735951baa311c66353405dcac39375dd66441db0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=735951baa311c66353405dcac39375dd66441db0

Commit description:

Currently, the Tegra GPC DMA hardware requires the transfer length to
be a multiple of the max burst size configured for the channel. When a
client requests a transfer where the length is not evenly divisible by
the configured max burst size, the DMA hangs with partial burst at
the end.

Fix this by reducing the burst size to the largest power-of-2 value
that evenly divides the transfer length. For example, a 40-byte
transfer with a 16-byte max burst will now use an 8-byte burst
(40 / 8 = 5 complete bursts) instead of causing a hang.

This issue was observed with the PL011 UART driver where TX DMA
transfers of arbitrary lengths were stuck.

Fixes: ee17028 ("dmaengine: tegra: Add tegra gpcdma driver")
Cc: stable@vger.kernel.org
Signed-off-by: Kartik Rajput <kkartik@nvidia.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://patch.msgid.link/20260422064134.1323610-1-kkartik@nvidia.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/dma/tegra186-gpc-dma.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=735951baa311c66353405dcac39375dd66441db0

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

The original Linux kernel CVE announcement for CVE-2026-72149 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72149

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).