[CVE-2026-80739][LOW] net/mlx5e: TC, Check if flow is PEER before acquiring devcom lock [ Upstream

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

CVE: CVE-2026-80739
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/mlx5e: TC, Check if flow is PEER before acquiring devcom lock [ Upstream
Commit: 607adbda01053abf5f93e322fe39325da8828cb8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=607adbda01053abf5f93e322fe39325da8828cb8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80739
Analysis date: Thu, 03 Sep 2026 05:25:43 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
mlx5e TC peer flow cleanup can recursively acquire the ESW devcom lock during failed peer FDB flow creation, causing a local CAP_NET_ADMIN reachable deadlock and denial of service on affected mlx5 eswitch setups.

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

The original Linux kernel CVE announcement for CVE-2026-80739 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80739

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: 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
======================================================================

CVE-2026-80739	LOW	https://www.kernelcve.org/list/?q=CVE-2026-80739 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'mlx5e TC peer flow cleanup can deadlock because mlx5e_tc_del_flow may try to acquire the ESW devcom lock while the same lock is already held during peer flow creation failure handling. The trigger is local control plane configuration of TC flower offload on mlx5 eswitch or representor setups, especially when lower level FDB flow creation fails and cleanup is invoked for a peer flow. For the CVSS the PR:L is used in the paranoid interpretation because CAP_NET_ADMIN may be delegated to a reduced capability root, container root, or network service account even though normal host administration often makes it PR:H. The issue is not directly network reachable and is not triggered by packet traffic alone. Impact is denial of service through a stuck lock path and stalled TC offload or network configuration operations, with no evidence of memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-80739 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE LOCK DEADLOCK 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
======================================================================

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Reliable kernel crash / strong DoS: +1
  The patch fixes an AA recursive lock deadlock in the mlx5e TC peer-flow cleanup path. This can stall the task performing TC offload configuration or cleanup.

* Availability impact realistic: +1 in paranoid only
  The deadlock can block network control-plane operations on affected mlx5 eswitch setups. I count this only in the paranoid score because the impact is not shown as a broad host-wide panic.

Subtracted signals:

* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2 conservative
  Creating or modifying TC flower offload rules normally requires CAP_NET_ADMIN or root-level network administration.

* Rare AND difficult-to-reach subsystem/configuration: -1
  The issue requires Mellanox mlx5 hardware, eswitch/devcom peer devices, duplicated TC offload, and a lower-level FDB flow creation failure.

Paranoid privilege interpretation:

* The full -2 privilege penalty is relaxed to -1 in the paranoid score because CAP_NET_ADMIN may be delegated to a container root, reduced-capability root, or network service account. This still does not make the issue unprivileged.

No awarded signals:

* No remote reachable / network-triggerable signal. Packet traffic alone does not trigger the issue.
* No generic memory corruption. The patch shows recursive locking, not UAF, OOB, double-free, type confusion, or stale pointer reuse.
* No privilege escalation plausible. There is no concrete primitive for write, object replacement, callback control, or credential impact.
* No confidentiality or integrity impact.

## 3. Reachability analysis

The trigger is a local network control-plane operation through TC flower offload configuration on mlx5 representor or eswitch setups. In normal deployments this requires CAP_NET_ADMIN or equivalent administrative control. Namespace or container delegation can lower the practical privilege boundary if a reduced-capability container or service account is allowed to configure the relevant TC offload objects, but this is still not PR:N.

The path is not a common packet receive or transmit data path. It depends on specific mlx5 hardware features, peer flow duplication, devcom locking, and an error path during FDB flow creation. Realistic exploitation is therefore configuration-dependent and mostly useful as a local privileged or semi-privileged DoS.

Call-site confidence: high. The supplied trace and diff show the relevant path from tc_new_tfilter to mlx5e_configure_flower, __mlx5e_add_fdb_flow, mlx5e_flow_put, and mlx5e_tc_del_flow.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel issue rather than an Important-class vulnerability. The demonstrated failure mode is a deadlock in a driver control-plane cleanup path. There is no evidence of memory corruption, privilege escalation, information disclosure, or direct network reachability.

The paranoid score is slightly higher only because delegated CAP_NET_ADMIN environments can make the trigger more accessible than full host-root administration. Even then, the bug remains DoS-only and hardware/configuration-specific.

## 5. One-sentence report phrase

mlx5e TC peer flow cleanup can recursively acquire the ESW devcom lock during failed peer FDB flow creation, causing a local CAP_NET_ADMIN reachable deadlock and denial of service on affected mlx5 eswitch setups.

## 6. Manual review recommendation

NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED

Reason: the patch shows a lock-ordering deadlock only, with no UAF, OOB access, stale pointer traversal, arbitrary write, credential impact, or network packet trigger.

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

Patch: net/mlx5e: TC, Check if flow is PEER before acquiring devcom lock [ Upstream
Commit: 607adbda01053abf5f93e322fe39325da8828cb8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=607adbda01053abf5f93e322fe39325da8828cb8

Changed files:
  drivers/net/ethernet/mellanox/mlx5/core/en/tc_priv.h
  drivers/net/ethernet/mellanox/mlx5/core/en_tc.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=607adbda01053abf5f93e322fe39325da8828cb8

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

The original Linux kernel CVE announcement for CVE-2026-80739 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80739

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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).