[CVE-2026-72140][MODERATE REGULAR] i2c: mlxbf: Fix use-after-free in mlxbf_i2c_init_resource()

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

CVE: CVE-2026-72140
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: i2c: mlxbf: Fix use-after-free in mlxbf_i2c_init_resource()
Commit: 6a108c9f5a81bb7b29dbb1398be0089655b6bfd2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6a108c9f5a81bb7b29dbb1398be0089655b6bfd2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72140
Analysis date: Sat, 15 Aug 2026 14:29:45 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Borderline manual review because UAF class
Manual review required: NO

Summary:
A constrained use-after-free read in the BlueField I2C driver error path can occur during resource initialization failure, but practical triggering is limited to local device-management or firmware/resource-control scenarios and mainly supports DoS-level impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72140 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72140

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72140	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';*CWE-416;CWE-825;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A use after free read exists in mlxbf_i2c_init_resource() because tmp_res is freed before the code reads tmp_res io to derive the error return from a failed devm_platform_get_and_ioremap_resource() call. The trigger is limited to the driver probe or resource initialization error path on Mellanox BlueField I2C hardware, so it is not network reachable and normally requires control over driver binding, module loading, firmware resources, or a similar local management path. For the CVSS the PR:L is used only for the paranoid score because a delegated local service account or reduced capability root with device management access may be able to force reprobe or resource failure without full host administration. Impact is at least a local denial of service via KASAN report, driver probe failure, or possible kernel crash. The observed primitive is an invalid read after free, so privilege escalation is not strongly supported, but the UAF class should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline manual review because UAF class (with actual score 2)	YES	USB UAF LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScoreLower=1
ActionableScore=3

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Borderline manual review because UAF class**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is a real use-after-free, but the observed operation is a read of `tmp_res->io` immediately after `devm_kfree(tmp_res)`, used only to return `PTR_ERR()`.
* Real lifetime corruption: +1
  The patch fixes an object lifetime ordering bug: read error code first, free object after.
* Requires admin/root/device-management in typical deployments: -2
  Triggering this path normally requires driver probe/reprobe, platform resource failure, module/device binding control, firmware/resource manipulation, or similar privileged management.
* Availability impact realistic: +1
  The realistic effect is probe failure, KASAN report, warning, or possible crash on affected systems.
* Rare hardware/device-specific condition: -1
  The affected driver is specific to Mellanox/NVIDIA BlueField I2C hardware.

Paranoid adjustments:

* Privileged kernel/device-management memory corruption path: +1
  The UAF occurs in a trusted driver initialization path tied to platform resources.
* Reduced-capability management scenario: +1 effective adjustment
  In some environments, a service account, container root with delegated device control, or reduced-capability root may influence driver reprobe/resource failure without full host-root equivalence.

No strong LPE signal is awarded. No attacker-controlled reclaim, write-after-free, callback dispatch, type confusion, refcount takeover, or arbitrary write primitive is shown.

## 3. Reachability analysis

The bug is local and device-specific. It is reached only when `devm_platform_get_and_ioremap_resource()` fails during `mlxbf_i2c_init_resource()`. A normal unprivileged user cannot typically force this path. Practical triggering usually requires control over driver binding, reprobe, module/device management, platform firmware/resource state, or equivalent administrative access on a BlueField system.

Namespaces and containers do not normally make this reachable unless device management capabilities are delegated into the container or service context. The path is not network reachable.

Call-site confidence: medium. The changed code is in the direct error path, but broader probe/reprobe call paths are not fully included in the supplied diff.

## 4. Severity interpretation

This behaves more like a Low-to-Moderate kernel UAF cleanup issue than an Important-class vulnerability. The theoretical concern comes from the UAF class, but the concrete primitive is a constrained invalid read after free in an initialization error path. Realistic exploitation evidence supports local DoS or diagnostic failure, not privilege escalation.

The paranoid score keeps it in manual-review territory because early kernel UAF triage should avoid false-negative closure, but the patch does not support escalating this into a strong LPE or broad memory corruption case.

## 5. One-sentence report phrase

A constrained use-after-free read in the BlueField I2C driver error path can occur during resource initialization failure, but practical triggering is limited to local device-management or firmware/resource-control scenarios and mainly supports DoS-level impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real UAF class bug, but the primitive is highly constrained and device-management gated. It should not be treated as Important without additional evidence of attacker-controlled reuse, write access, or privilege-escalation mechanics.

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

Patch: i2c: mlxbf: Fix use-after-free in mlxbf_i2c_init_resource()
Commit: 6a108c9f5a81bb7b29dbb1398be0089655b6bfd2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6a108c9f5a81bb7b29dbb1398be0089655b6bfd2

Commit description:

If devm_platform_get_and_ioremap_resource() returns an error,
mlxbf_i2c_init_resource() frees tmp_res before reading tmp_res->io to
get the error code. This results in a use-after-free.

Save the error code before freeing tmp_res.

Fixes: b5b5b32 ("i2c: mlxbf: I2C SMBus driver for Mellanox BlueField SoC")
Signed-off-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260714150808.85045-1-xuanqiang.luo@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/i2c/busses/i2c-mlxbf.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=6a108c9f5a81bb7b29dbb1398be0089655b6bfd2

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

The original Linux kernel CVE announcement for CVE-2026-72140 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72140

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 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).