[CVE-2026-72006][LOW] net/mlx5: free mlx5_st_idx_data on final dealloc commit df6134b527a88b3e65ba6ae5073664af091d5fd2 upstream.

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

CVE: CVE-2026-72006
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/mlx5: free mlx5_st_idx_data on final dealloc commit df6134b527a88b3e65ba6ae5073664af091d5fd2 upstream.
Commit: 262da8b6ea03d01ee7ed01ad309e4c89941f6b14
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=262da8b6ea03d01ee7ed01ad309e4c89941f6b14
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72006
Analysis date: Sat, 15 Aug 2026 19:46:02 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing kfree in the mlx5 steering-tag index deallocation path leaks one mlx5_st_idx_data object per final mkey release cycle, allowing a local RDMA-capable workload to cause gradual memory exhaustion but not showing evidence of memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72006 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72006

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-2026-72006	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-401;*CWE-772;**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 ST index bookkeeping can leak one mlx5_st_idx_data object when the final reference to a steering tag table entry is dropped. The leak occurs because the entry is removed from the xarray but the backing allocation is not freed, so repeated allocation and release of mkeys with TPH steering tag hints can grow the kmalloc slab over time. For the CVSS the PR:L is used because a local user or local process with access to RDMA mlx5 resources may be able to churn memory registrations without full administrator privileges in some deployments. The issue is not directly network reachable because a remote peer does not directly call the mkey allocation and release path. Impact is denial of service through gradual memory exhaustion. No confidentiality or integrity impact is assigned because the patch shows a resource leak without a UAF, OOB access, info leak, or arbitrary write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-72006 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE LEAK NETWORK HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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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 non-admin trigger possible: +1. A local process with access to mlx5 RDMA resources may be able to repeatedly allocate and release MRs or mkeys carrying TPH steering-tag hints.
* Rare and configuration-dependent exposure: -1. This requires mlx5 hardware, steering-tag support, and workloads that churn relevant mkeys.
* Availability impact realistic: +1. Sustained leaking can grow the kmalloc slab over time and may eventually contribute to memory exhaustion.

Paranoid additional interpretation:

* Resource exhaustion DoS concern: +1. If an authorized local RDMA workload can churn these objects at high rate, the leak can become operationally relevant.
* No memory corruption signal is awarded. The patch adds a missing kfree after xa_erase, which indicates a leak of unreachable memory, not UAF, double free, OOB access, arbitrary write, or stale object reuse.

## 3. Reachability analysis

The issue is not remotely network-triggerable in the usual sense. A remote peer does not directly invoke mlx5_st_dealloc_index or allocate and release local mlx5 steering-tag mkeys. Triggering requires a local workload or service that can create and destroy relevant RDMA MRs or mkeys with TPH steering-tag hints.

Namespaces and containers may matter only if RDMA device access is delegated into a container or to a non-root service account. This supports PR:L style practical reachability, but not broad unprivileged local reachability. The path is hardware and feature dependent, and not a generic default kernel path.

Call-site confidence: medium. The patch shows the final deallocation point and the missing kfree directly, but the full allocation and userspace reachability path is inferred from mlx5 RDMA mkey and MR behavior described in the commit.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak, not an Important-class kernel vulnerability. The realistic impact is gradual memory consumption under repeated allocation and release cycles. There is no supported privilege escalation path, no confidentiality impact, and no integrity impact.

Theoretical worst case is local DoS via sustained memory exhaustion. The patch context does not support upgrading this to memory corruption, LPE, or a security-boundary bypass.

## 5. One-sentence report phrase

A missing kfree in the mlx5 steering-tag index deallocation path leaks one mlx5_st_idx_data object per final mkey release cycle, allowing a local RDMA-capable workload to cause gradual memory exhaustion but not showing evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED. This is a resource leak with hardware and workload-specific reachability, no concrete memory corruption primitive, and no network or privilege-escalation evidence.

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

Patch: net/mlx5: free mlx5_st_idx_data on final dealloc commit df6134b527a88b3e65ba6ae5073664af091d5fd2 upstream.
Commit: 262da8b6ea03d01ee7ed01ad309e4c89941f6b14
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=262da8b6ea03d01ee7ed01ad309e4c89941f6b14

Commit description:

Workloads that repeatedly allocate and release mkeys carrying TPH
steering-tag hints (e.g. churning RDMA MRs) leak one
struct mlx5_st_idx_data per cycle; kmemleak flags it as unreferenced
and the kmalloc slab grows over time.

When the last reference to an ST table entry is dropped,
mlx5_st_dealloc_index() removed the entry from idx_xa but the backing
mlx5_st_idx_data allocation was never freed.

Free idx_data after the xa_erase() so the lifetime of the bookkeeping
struct matches the lifetime of the ST entry it tracks.

Cc: stable@vger.kernel.org
Fixes: 888a7776f4fb ("net/mlx5: Add support for device steering tag")
Reviewed-by: Michael Gur <michaelgur@nvidia.com>
Signed-off-by: Zhiping Zhang <zhipingz@meta.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260702222507.1234467-1-zhipingz@meta.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/net/ethernet/mellanox/mlx5/core/lib/st.c 1

Changed files:
  drivers/net/ethernet/mellanox/mlx5/core/lib/st.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=262da8b6ea03d01ee7ed01ad309e4c89941f6b14

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

The original Linux kernel CVE announcement for CVE-2026-72006 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72006

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).