[CVE-2026-72308][LOW] mlxsw: fix refcount leak in mlxsw_sp_port_lag_join()

[CVE-2026-72308][LOW] mlxsw: fix refcount leak in mlxsw_sp_port_lag_join()

[AL-KERNEL]

CVE: CVE-2026-72308
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mlxsw: fix refcount leak in mlxsw_sp_port_lag_join()
Commit: 8b3350eacd9df0597bfe36a594df7b9def0b3edf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b3350eacd9df0597bfe36a594df7b9def0b3edf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72308
Analysis date: Sun, 16 Aug 2026 06:31:58 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missed cleanup path in `mlxsw_sp_port_lag_join()` can leak a LAG reference after `mlxsw_sp_port_lag_index_get()` fails, causing a local privileged resource leak with possible denial of service after repeated attempts.

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

The original Linux kernel CVE announcement for CVE-2026-72308 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72308

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-2026-72308	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-772;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'mlxsw_sp_port_lag_join() can leak a LAG reference when mlxsw_sp_port_lag_index_get() fails after mlxsw_sp_lag_get() has already taken the reference. This is a refcount leak and resource management bug rather than a use after free or direct memory corruption primitive. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate CAP_NET_ADMIN or LAG management to a reduced capability root, container root, or network service account. The issue is not network reachable through packet traffic and requires local control plane access to mlxsw LAG configuration on affected hardware. Impact is mainly denial of service through accumulated leaked references or failed cleanup after repeated trigger attempts, with no strong evidence for confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE SIMPLEFIX LEAK ERRORPATH NETWORK  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Real lifetime corruption: +1
  This is a refcount lifetime bug. `mlxsw_sp_lag_get()` takes a LAG reference, but one error path returned directly without the matching `mlxsw_sp_lag_put()`.

* Availability impact realistic: +1 in paranoid scoring only
  Repeated triggering could accumulate leaked LAG references and cause cleanup failures or resource exhaustion. The patch does not show an immediate crash, UAF, double free, overwrite, or strong corruption primitive.

Subtracted signals:

* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2 conservative, -1 paranoid
  Joining a port to a LAG through mlxsw networking control paths normally requires administrative network configuration privileges. Paranoid scoring uses a smaller penalty because some environments may delegate CAP_NET_ADMIN or LAG management to container root, reduced-capability root, or a network management service account.

* Rare and hardware-specific condition: -1 conservative
  The affected path requires Mellanox mlxsw Spectrum hardware and a failing `mlxsw_sp_port_lag_index_get()` path during LAG join.

Not awarded:

* No remote/network-triggerable signal. Packet traffic does not directly trigger this path.
* No generic memory corruption signal. This is a missed put/refcount leak, not UAF, double free, OOB write, or type confusion.
* No privilege escalation signal. The patch does not support attacker-controlled reclaim, stale object reuse, callback control, arbitrary write, or security-boundary bypass.

Call-site confidence: high. The patch shows the relevant error path and the intended cleanup label.

## 3. Reachability analysis

The bug is triggered through local control-plane configuration of mlxsw LAG membership. In normal deployments this requires CAP_NET_ADMIN or equivalent administrative privileges. Namespace or container setups may reduce the practical privilege barrier if CAP_NET_ADMIN is delegated to a container or service account, but this is still not a fully unprivileged local trigger.

The path is not reachable from ordinary network packets. It also depends on affected mlxsw hardware and on an error from `mlxsw_sp_port_lag_index_get()`, so exploitation conditions are specific and not broadly default-exposed.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource lifetime bug. The theoretical impact is reference/resource leakage and possible denial of service after repeated failed LAG join attempts. Realistic exploitation evidence is weak because the patch only fixes a single missed cleanup path and does not show memory corruption, privilege escalation, or a reliable crash primitive.

It should not be treated as an Important-class kernel vulnerability.

## 5. One-sentence report phrase

A missed cleanup path in `mlxsw_sp_port_lag_join()` can leak a LAG reference after `mlxsw_sp_port_lag_index_get()` fails, causing a local privileged resource leak with possible denial of service after repeated attempts.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a localized refcount leak in a privileged, hardware-specific driver control path with no demonstrated memory corruption, privilege escalation, or remote reachability.

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

Patch: mlxsw: fix refcount leak in mlxsw_sp_port_lag_join()
Commit: 8b3350eacd9df0597bfe36a594df7b9def0b3edf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b3350eacd9df0597bfe36a594df7b9def0b3edf

Commit description:

When mlxsw_sp_port_lag_index_get() fails, mlxsw_sp_port_lag_join()
returns an error without releasing the lag reference obtained by
the earlier mlxsw_sp_lag_get().  All other error paths in the
function jump to the cleanup label that ends with
mlxsw_sp_lag_put(), so this is a single missed release.

Fix the leak by replacing the bare 'return err' with a goto to the
existing error cleanup label, which will drop the reference safely.

Cc: stable@vger.kernel.org
Fixes: 0d65fc1 ("mlxsw: spectrum: Implement LAG port join/leave")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260609083709.209743-1-vulab@iscas.ac.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/ethernet/mellanox/mlxsw/spectrum.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=8b3350eacd9df0597bfe36a594df7b9def0b3edf

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

The original Linux kernel CVE announcement for CVE-2026-72308 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72308

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: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: 1

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).