[CVE-2026-72032][LOW] net/mlx5: HWS, fix matcher leak on resize target setup failure [ Upstream commit bb09d0e64ecaa0aa0f7d1133a1696ed74dead295 ]

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

CVE: CVE-2026-72032
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/mlx5: HWS, fix matcher leak on resize target setup failure [ Upstream commit bb09d0e64ecaa0aa0f7d1133a1696ed74dead295 ]
Commit: a751ccdc6ea9bde154f25a5ba66926f462f96c19
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a751ccdc6ea9bde154f25a5ba66926f462f96c19
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72032
Analysis date: Sat, 15 Aug 2026 11:08:46 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A failed mlx5 HWS matcher resize-target setup can leak the newly allocated replacement matcher, allowing repeated privileged or delegated local control-plane operations to cause resource exhaustion DoS on affected mlx5 HWS-capable systems.

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

The original Linux kernel CVE announcement for CVE-2026-72032 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72032

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-2026-72032	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-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 HWS matcher resize can leak a newly allocated replacement matcher when setting the resize target fails. Repeated local control-plane operations that force this failure path could consume kernel or device driver memory and eventually cause denial of service on systems with mlx5 HWS capable hardware. For the CVSS the PR:L value is used for the paranoid score because some deployments may allow a local user or service account with access to RDMA or flow steering interfaces to drive matcher operations without full host administrator privileges. The issue is not directly network reachable through normal packet traffic. Impact is resource exhaustion DoS only, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-72032 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE LEAK NETWORK HARDWARE TEST  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Resource leak / memory leak concern: counted qualitatively, but no positive memory-corruption signal. The patch fixes a leaked `new_matcher` object when `mlx5hws_matcher_resize_set_target()` fails.
* Requires admin/root/CAP or privileged device control in typical deployments: -2. HWS matcher resize and mlx5 steering control are normally not reachable by arbitrary remote traffic and typically require privileged RDMA, devlink, netdev, or driver-management access.
* Rare hardware / difficult-to-reach configuration: -1. The issue requires mlx5 HWS-capable hardware and the relevant steering resize path.
* Availability impact is possible but not immediate. A single failed resize leaks one matcher, and practical DoS would require repeated triggering, so this does not raise the conservative score above Low-like.

Paranoid signals:

* Local unprivileged or reduced-privilege trigger: +1. In some deployments, RDMA or flow-steering access may be delegated to a local service account, container, or non-root workload with device access.
* Availability impact realistic: +1. Repeatedly forcing the resize-target failure path could accumulate leaked matcher objects and exhaust kernel or device-driver resources.
* Rare hardware / configuration limitation is noted, but the paranoid score keeps the issue visible because the leak occurs in a trusted device-management path.

Not applied:

* No generic memory corruption. The patch shows a missing destroy call, not UAF, double-free, OOB write, type confusion, or arbitrary write.
* No privilege escalation plausible. There is no reclaim, stale callback, attacker-controlled overwrite, or object confusion primitive.
* No network-triggerable signal. Normal packet traffic does not appear to reach this path directly.
* No confidentiality or integrity impact. The demonstrated effect is resource leakage only.

## 3. Reachability analysis

The bug is reachable through mlx5 HWS matcher resize handling, not through the normal packet receive or transmit path. In typical deployments, triggering it requires local control over mlx5 hardware steering objects, RDMA or related privileged device-management interfaces. Namespace or container setups may reduce the effective privilege requirement if device access or RDMA resources are delegated, but this is deployment-specific. The path is hardware-specific and requires mlx5 HWS-capable devices, so exposure is narrower than core networking or common syscall paths.

Call-site confidence: medium. The changed code is local and clear, but the full user-facing call chain that can repeatedly force `mlx5hws_matcher_resize_set_target()` failure is not present in the supplied patch.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate resource leak, not an Important-class kernel vulnerability. The theoretical impact is denial of service through repeated resource exhaustion, but the patch does not support memory corruption, privilege escalation, information disclosure, or unauthorized cross-boundary access. The paranoid score remains low because the vulnerability class is a leak in an error path and the affected path is hardware-specific and control-plane oriented.

## 5. One-sentence report phrase

A failed mlx5 HWS matcher resize-target setup can leak the newly allocated replacement matcher, allowing repeated privileged or delegated local control-plane operations to cause resource exhaustion DoS on affected mlx5 HWS-capable systems.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage purposes because it is a resource leak without a demonstrated memory-corruption primitive, remote trigger, confidentiality impact, integrity impact, or plausible privilege-escalation path.

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

Patch: net/mlx5: HWS, fix matcher leak on resize target setup failure [ Upstream commit bb09d0e64ecaa0aa0f7d1133a1696ed74dead295 ]
Commit: a751ccdc6ea9bde154f25a5ba66926f462f96c19
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a751ccdc6ea9bde154f25a5ba66926f462f96c19

Commit description:

hws_bwc_matcher_move() allocates a replacement matcher before setting it
as the resize target. If mlx5hws_matcher_resize_set_target() fails, the
replacement matcher is not attached anywhere and is leaked.

Fix the leak by destroying the replacement matcher before returning from
the resize-target failure path.

The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1.1.

An x86_64 allyesconfig build showed no new warnings. As we do not have a
mlx5 HWS-capable device to test with, no runtime testing was able to be
performed.

Fixes: 2111bb970c78 ("net/mlx5: HWS, added backward-compatible API handling")
Cc: stable@vger.kernel.org
Signed-off-by: Dawei Feng <dawei.feng@seu.edu.cn>
Reviewed-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260629064049.3852759-1-dawei.feng@seu.edu.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/net/ethernet/mellanox/mlx5/core/steering/hws/mlx5hws_bwc.c 1

Changed files:
  drivers/net/ethernet/mellanox/mlx5/core/steering/hws/mlx5hws_bwc.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=a751ccdc6ea9bde154f25a5ba66926f462f96c19

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

The original Linux kernel CVE announcement for CVE-2026-72032 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72032

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: 0
  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).