[CVE-2026-45973][MODERATE REGULAR] RDMA/mlx5: Fix UMR hang in LAG error state unload [ Upstream

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

CVE: CVE-2026-45973
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/mlx5: Fix UMR hang in LAG error state unload [ Upstream
Commit: c8fb5c965ac7d0104872a8e4f6451f3bc6328199
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8fb5c965ac7d0104872a8e4f6451f3bc6328199
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45973
Analysis date: Wed, 27 May 2026 09:15:52 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45973 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45973

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: 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
======================================================================

CVE-2026-45973	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'RDMA mlx5 in LAG mode can hang indefinitely during device unload after a firmware reset because the bond device may miss sys_error handling while a slave is already dead. UMR requests can be posted successfully but their completions never arrive, leaving deregistration or uverbs cleanup stuck in the teardown path. For the CVSS the PR:N is used only for the paranoid adjacent/device mediated case where firmware or fabric failure conditions may influence reset handling without local privileges on the victim. In the realistic base case triggering requires administrative device management, driver unload, or firmware reset conditions on a host using mlx5 LAG. The issue is not Internet reachable and has no evidence of memory corruption, information disclosure, or privilege escalation. Impact is denial of service through an indefinite RDMA device unload or reset hang.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	INIT RACE NETWORK HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

2. Signal breakdown
* Reliable kernel hang / strong DoS: +1. The commit describes an indefinite wait for UMR completion during device unload.
* Firmware-mediated external influence: +1 in paranoid scoring. The trigger involves firmware reset and LAG error-state propagation, which may be influenced by device or fabric failure conditions rather than only local code.
* Privileged kernel/device-management path: +1. The hang occurs in RDMA/mlx5 device teardown, unload, firmware reset, and IB unregister paths.
* Availability impact realistic: +1. The unload/reset path can hang forever and block RDMA/uverbs cleanup.
* Broad data-center deployment relevance: +1 in paranoid scoring. mlx5 RDMA is common in high-performance data-center environments, though this specific bug requires LAG mode.
* Requires admin/device-management conditions in the conservative case: -2. Reliable local triggering normally requires driver unload, firmware reset, eswitch/LAG changes, or equivalent host/device control.
* Configuration-specific LAG condition: -1. The issue requires mlx5 LAG mode and the master/slave sys_error ordering problem.
* No memory corruption: +0. The patch fixes notifier ordering and error-state propagation, not UAF, OOB write, arbitrary write, or page-cache corruption.
* No confidentiality or integrity primitive: +0. The demonstrated impact is hang only.

3. Reachability analysis
The affected path is RDMA/mlx5 teardown during firmware reset in LAG mode. A host administrator or device-management process can trigger it through unload/reset/LAG or eswitch transitions. In some environments, firmware or fabric failure conditions may externally influence reset timing, but this is adjacent/device-mediated rather than general network reachability. Containers do not normally gain access unless they are delegated RDMA device-management capabilities. The bug is not default-exposed on all mlx5 systems and requires LAG mode.

4. Severity interpretation
This behaves like a borderline Moderate availability issue. The realistic impact is an indefinite driver unload or RDMA cleanup hang, not memory corruption or privilege escalation. It deserves manual review for mlx5 LAG deployments because RDMA teardown hangs can affect production nodes and recovery automation, but it is not an Important-class kernel vulnerability without stronger evidence of remote control or corruption.

5. One-sentence report phrase
In mlx5 RDMA LAG mode, firmware reset can cause sys_error events to miss the bond device and leave UMR completions waiting forever during device unload, resulting in an availability-impacting teardown hang.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review is recommended for systems using mlx5 RDMA with LAG because the DoS is persistent and device-mediated, but no memory corruption, information disclosure, or privilege escalation is shown.

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

Patch: RDMA/mlx5: Fix UMR hang in LAG error state unload [ Upstream
Commit: c8fb5c965ac7d0104872a8e4f6451f3bc6328199
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8fb5c965ac7d0104872a8e4f6451f3bc6328199

Changed files:
  drivers/infiniband/hw/mlx5/main.c
  drivers/infiniband/hw/mlx5/mlx5_ib.h

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=c8fb5c965ac7d0104872a8e4f6451f3bc6328199

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

The original Linux kernel CVE announcement for CVE-2026-45973 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45973

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:A/AC:H/PR:N/UI:N/S:U/C:N/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: 2
  Paranoid ActionableScore: 4

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).