[CVE-2026-74297][MODERATE 7.0] RDMA/mlx5: Fix undefined shift of user RQ WQE size [ Upstream

[CVE-2026-74297][MODERATE 7.0] RDMA/mlx5: Fix undefined shift of user RQ WQE size [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74297
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/mlx5: Fix undefined shift of user RQ WQE size [ Upstream
Commit: 9fff54929cc00849d738faa99f06c32399aeb026
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fff54929cc00849d738faa99f06c32399aeb026
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74297
Analysis date: Sun, 16 Aug 2026 01:54:59 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A user-controlled `rq_wqe_shift` in the mlx5 RDMA uverbs QP creation path can trigger undefined left-shift behavior and invalid RQ WQE sizing, creating a local DoS risk and a weak device-queue corruption concern that should be manually reviewed.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74297 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74297

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-2026-74297	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-190;CWE-682;CWE-758;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.6';DESCR 'An undefined left shift in the RDMA mlx5 userspace QP creation path can occur because set_rq_size computes the RQ WQE size from a user controlled rq_wqe_shift value. Values such as 31 or 32 can overflow or exceed the valid signed shift range and may produce an invalid WQE size or an inconsistent max_gs value. For the CVSS the PR:L is used because reliable triggering requires local access to the RDMA uverbs device, but this access can be available to non root users through an rdma group or a service account. The issue is not directly network reachable and requires local interaction with the RDMA device interface. Base impact is likely local denial of service or invalid queue setup. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives. Impact may include limited confidentiality or integrity impact if the bad size calculation reaches later queue or WQE handling code, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	SIMPLEFIX NETWORK  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: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The value comes from a user command through the RDMA uverbs QP creation path, and access may be available to non-root users via `/dev/infiniband/uverbsX` permissions or an `rdma` group.
* Weak or indirect corruption candidate: +1. The patch fixes an undefined shift in a user-controlled size calculation that affects RQ WQE sizing and `max_gs`, but it does not show a concrete UAF, OOB write, arbitrary write, or reclaim primitive.
* Availability impact plausible: +1. Invalid queue sizing or undefined behavior can plausibly cause failed queue setup, WARN/Oops, or device/driver instability, but no reliable crash path is demonstrated.

Paranoid additional signals:

* Local high-control device object layout concern: +1. The user-controlled shift affects RDMA queue/WQE layout-related values, which are later used by a trusted device driver path.
* DMA-adjacent driver metadata concern: +1. RQ WQE sizing is close to RDMA queue and device-facing metadata, so a bad size calculation deserves manual review even though the patch only proves validation failure.
* Validation-only cap applied. This is primarily an input-validation fix using `check_shl_overflow()`, so the paranoid score is capped at 5 without a concrete downstream corruption primitive.

Not awarded:

* No remote/network-triggerable score. This is not packet-triggered.
* No strong LPE score. No attacker-controlled reclaim, arbitrary write, type confusion, callback control, or refcount takeover is shown.
* No strong memory corruption score. The patch shows undefined behavior and bad size calculation, not a demonstrated write primitive.

## 3. Reachability analysis

The likely trigger is a local process that can access the mlx5 RDMA userspace verbs device and create or configure a QP with a crafted `rq_wqe_shift`. In typical deployments this does not require full root if uverbs access is delegated to a user or service account, so PR-like reasoning is closer to local low privilege than administrator-only. Containers or workloads with passed-through RDMA devices may also reduce the practical privilege barrier.

The path is hardware and configuration dependent because it requires mlx5 RDMA-capable hardware and exposed uverbs access. It is not a default network attack surface and cannot be triggered merely by sending packets to the host.

Call-site confidence: medium. The patch shows the vulnerable calculation and immediate use in RQ sizing fields, but not all later consumers of `wqe_shift`, `wqe_size`, and `max_gs`.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than an ordinary Moderate because the invalid value is user-controlled and affects RDMA queue sizing in a trusted driver path. The realistic evidence supports local DoS or invalid queue/device state. Theoretical memory corruption or privilege escalation is not proven, but the queue-layout and DMA-adjacent context make auto-closing risky without manual review.

## 5. One-sentence report phrase

A user-controlled `rq_wqe_shift` in the mlx5 RDMA uverbs QP creation path can trigger undefined left-shift behavior and invalid RQ WQE sizing, creating a local DoS risk and a weak device-queue corruption concern that should be manually reviewed.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not a proven Important-class memory corruption bug, but the affected value influences RDMA queue sizing and device-facing metadata from a local userspace API, so it should not be auto-closed based only on the small validation patch.

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

Patch: RDMA/mlx5: Fix undefined shift of user RQ WQE size [ Upstream
Commit: 9fff54929cc00849d738faa99f06c32399aeb026
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fff54929cc00849d738faa99f06c32399aeb026

Changed files:
  drivers/infiniband/hw/mlx5/qp.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=9fff54929cc00849d738faa99f06c32399aeb026

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

The original Linux kernel CVE announcement for CVE-2026-74297 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74297

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:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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).