[CVE-2026-74396][LOW] RDMA/mlx5: Fix UMR XLT cleanup on ODP populate failure [ Upstream

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

CVE: CVE-2026-74396
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: RDMA/mlx5: Fix UMR XLT cleanup on ODP populate failure [ Upstream
Commit: ffa85a2c197935ace6f1634ad9eb0a44bc615670
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffa85a2c197935ace6f1634ad9eb0a44bc615670
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74396
Analysis date: Sun, 16 Aug 2026 05:03:15 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
RDMA mlx5 UMR XLT cleanup can be skipped after ODP populate failure, leaking a DMA mapped buffer and possibly leaving the emergency XLT mutex locked, causing RDMA denial of service under specific mlx5 ODP conditions.

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

The original Linux kernel CVE announcement for CVE-2026-74396 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74396

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74396	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'RDMA mlx5 UMR XLT cleanup can be skipped when mlx5_odp_populate_xlt fails during ODP population. This leaks the DMA mapped XLT buffer and may also leave the emergency XLT page mutex locked, which can block later RDMA operations that need the same emergency resource. For the CVSS the PR:L is used because reliable triggering normally requires a local process or authorized RDMA workload with access to mlx5 RDMA verbs or an already established RDMA context. The issue is not reachable over ordinary IP networking. A more conservative adjacent network view is possible for RDMA deployments where a peer can drive ODP activity after local setup. Impact is denial of service through resource leakage or RDMA path deadlock, with no concrete evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	SIMPLEFIX LEAK ERRORPATH NETWORK DMAorINTERRUPT 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**

## 2. Signal breakdown

Conservative signals:

* Local privileged or authorized local workload trigger: +0
  Triggering normally requires access to mlx5 RDMA verbs or an already configured RDMA/ODP workload. This is not a generic unprivileged local interface.
* Reliable RDMA subsystem DoS concern: +1
  The skipped cleanup can leak a DMA mapped XLT buffer and may leave `xlt_emergency_page_mutex` locked, potentially blocking later RDMA operations.
* Hard or condition dependent trigger: -1
  The issue requires `mlx5_odp_populate_xlt()` to fail after XLT allocation and DMA mapping.
* Rare and configuration dependent subsystem: -1
  Requires mlx5 RDMA with ODP/UMR paths, not a default broad kernel path.
* Availability impact realistic: +1
  Resource leakage and a stuck emergency mutex can degrade or block RDMA functionality.

Paranoid additions:

* Local unprivileged or tenant workload trigger: +1
  In some RDMA deployments, non-root users or tenants may have access to RDMA verbs after device and permissions are configured.
* Availability impact treated as stronger: +1
  If the emergency page mutex remains locked, the effect can persist for the affected RDMA path until recovery or device reset.

Not awarded:

* No generic memory corruption bonus. The patch shows a leak and missed unlock, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No privilege escalation bonus. There is no demonstrated reclaim, overwrite, callback control, refcount abuse, or cross-boundary primitive.
* No remote reachable bonus. This is not reachable over ordinary IP networking. RDMA peer influence is deployment dependent and not enough to score as remote network trigger.

## 3. Reachability analysis

The realistic trigger is a local process or authorized workload using mlx5 RDMA ODP/UMR functionality, combined with a failure from `mlx5_odp_populate_xlt()`. In multi-tenant HPC or storage environments, RDMA verbs may be delegated to non-root users, which supports the paranoid PR:L style interpretation. In typical systems without mlx5 RDMA ODP exposure, the affected path is not reachable. Containers or namespaces only matter if RDMA device access is explicitly passed through.

Call-site confidence: medium. The patch and commit message clearly describe allocation, DMA mapping, skipped cleanup, and mutex state, but the full caller tree and exact user trigger conditions are not included.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource cleanup bug, not an Important-class memory corruption issue. Theoretical impact is denial of service through DMA mapping or memory leakage and possible RDMA path blocking. Realistic exploitation evidence does not support privilege escalation, information disclosure, or kernel memory corruption.

## 5. One-sentence report phrase

RDMA mlx5 UMR XLT cleanup can be skipped after ODP populate failure, leaking a DMA mapped buffer and possibly leaving the emergency XLT mutex locked, causing RDMA denial of service under specific mlx5 ODP conditions.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch supports a resource leak and missed mutex cleanup only, with no concrete memory corruption or privilege escalation primitive and no ordinary network reachability.

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

Patch: RDMA/mlx5: Fix UMR XLT cleanup on ODP populate failure [ Upstream
Commit: ffa85a2c197935ace6f1634ad9eb0a44bc615670
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffa85a2c197935ace6f1634ad9eb0a44bc615670

Changed files:
  drivers/infiniband/hw/mlx5/umr.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=ffa85a2c197935ace6f1634ad9eb0a44bc615670

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

The original Linux kernel CVE announcement for CVE-2026-74396 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74396

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:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.8

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).