[CVE-2026-74397][LOW] IB/mlx5: Fix transport-domain rollback and initialize lb mutex earlier [ Upstream

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

CVE: CVE-2026-74397
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: IB/mlx5: Fix transport-domain rollback and initialize lb mutex earlier [ Upstream
Commit: 2c3b2667dad69d56774b79db763acb3a1bee0fc0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c3b2667dad69d56774b79db763acb3a1bee0fc0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74397
Analysis date: Sun, 16 Aug 2026 05:15:24 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
`mlx5_ib_alloc_transport_domain could leak a Transport Domain if local loopback enable failed after allocation, allowing repeated local device-context operations to potentially exhaust mlx5 RDMA resources and cause denial of service.`

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

The original Linux kernel CVE announcement for CVE-2026-74397 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74397

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: NO

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

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

CVE-2026-74397	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-665;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'mlx5_ib_alloc_transport_domain can allocate a Transport Domain and then fail while enabling local loopback support, leaving the allocated domain unreleased. Repeated triggering of this error path could exhaust mlx5 or RDMA device resources and cause denial of service for users of the affected adapter. For the CVSS the PR:L is used because reliable triggering requires local access to the RDMA device or a process context allowed to create mlx5 RDMA user contexts, rather than only remote packet delivery. The issue is not directly network reachable and does not provide an evident memory corruption primitive. Impact is resource exhaustion and denial of service only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	INIT SIMPLEFIX LEAK NETWORK LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	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**::

## 2. Signal breakdown

Conservative signals:

* Local reachable device API: **+1**. Triggering likely requires a local process able to create mlx5 RDMA user contexts or otherwise exercise the mlx5 IB device path.
* Rare AND hardware-dependent subsystem: **-1**. The issue requires mlx5 RDMA hardware and the affected loopback capability path.
* Availability impact possible: **+1**. A leaked Transport Domain can cause resource exhaustion if the failure path is repeated.
* Hard or unreliable triggering condition: **-1**. The leak requires `mlx5_ib_enable_lb()` to fail after TD allocation, which is a specific error path rather than a normal fast-path operation.
* Final conservative: **1**

Paranoid additions:

* Firmware-mediated or device-state influence: **+1**. The failure path may depend on mlx5 firmware or device capability behavior, so an external device or firmware condition could influence whether the leak is reachable.
* Final paranoid: **2**

Not awarded:

* No generic memory corruption. The patch fixes a resource leak and initialization ordering, not UAF, double-free, OOB write, refcount takeover, or type confusion.
* No privilege escalation plausible signal. No reclaim, overwrite, callback control, stale object reuse, or cross-boundary primitive is shown.
* No remote/network-triggerable signal. RDMA network traffic alone is not shown to directly trigger the allocation failure path.
* No strong DoS signal. Resource exhaustion is possible only through repeated triggering of a specific error path.

## 3. Reachability analysis

The likely trigger is local access to the mlx5 RDMA device or a process context permitted to create mlx5 IB ucontexts. This is not a general remote network attack surface. Namespaces or containers may matter only if RDMA device access is delegated into the container, but that still requires explicit device exposure or permissions. The affected code is hardware-specific and depends on mlx5 capabilities and loopback handling. Realistic exploitation requires repeatedly hitting an error path after successful Transport Domain allocation, so reliability is limited.

Call-site confidence: **medium**. The changed function and immediate error handling are visible, but broader caller behavior and practical ability to force `mlx5_ib_enable_lb()` failure are not fully shown in the supplied patch.

## 4. Severity interpretation

This behaves like an ordinary Low or Moderate resource leak rather than an Important kernel vulnerability. The theoretical impact is denial of service through exhaustion of mlx5 or RDMA Transport Domain resources. The realistic evidence supports only constrained device-resource exhaustion, not memory corruption or privilege escalation. It should not be treated as an actionable Moderate or Important candidate based on the supplied patch.

## 5. One-sentence report phrase

`mlx5_ib_alloc_transport_domain could leak a Transport Domain if local loopback enable failed after allocation, allowing repeated local device-context operations to potentially exhaust mlx5 RDMA resources and cause denial of service.`

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

This can be auto-closed or handled in deferred mode unless the target product exposes mlx5 RDMA device access to untrusted users or has evidence that `mlx5_ib_enable_lb()` failure is easily and repeatedly triggerable.

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

Patch: IB/mlx5: Fix transport-domain rollback and initialize lb mutex earlier [ Upstream
Commit: 2c3b2667dad69d56774b79db763acb3a1bee0fc0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c3b2667dad69d56774b79db763acb3a1bee0fc0

Changed files:
  drivers/infiniband/hw/mlx5/main.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=2c3b2667dad69d56774b79db763acb3a1bee0fc0

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

The original Linux kernel CVE announcement for CVE-2026-74397 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74397

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:L/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).