[CVE-2026-98489][MODERATE REGULAR] net: atl1c: fix soft lockup on out-of-range tpd_cons read

[CVE-2026-98489][MODERATE REGULAR] net: atl1c: fix soft lockup on out-of-range tpd_cons read

[AL-KERNEL]

CVE: CVE-2026-98489
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: atl1c: fix soft lockup on out-of-range tpd_cons read
Commit: e7acd4cdeccbcdfd407adeb72b1eba14d1145b6f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7acd4cdeccbcdfd407adeb72b1eba14d1145b6f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98489
Analysis date: Mon, 19 Oct 2026 00:38:34 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An invalid atl1c hardware transmit consumer index can make the NAPI cleanup loop run indefinitely after an adjacent link reset, causing a CPU soft lockup and network denial of service without evidence of memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-98489 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98489

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: MODERATE REGULAR
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-2026-98489	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98489 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;*CWE-20;**CWE-400;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'The atl1c transmit cleanup path can enter an infinite loop when the NIC reports an out of range tpd_cons value such as 0xffff during a MAC reset or link state transition. The software cleanup index can never reach this value, so atl1c_clean_tx continues running and causes a NAPI thread or CPU soft lockup. A directly connected network device may trigger the required link flap by rebooting or resetting its port, but ordinary routed packet traffic is not shown to be sufficient. For the CVSS the PR:N value is used because an actor controlling the adjacent peer does not need an authenticated user context or privileges on the affected host. AV:A and AC:H reflect the need for direct network adjacency, affected atl1c hardware, and a specific reset or link transition. Impact is denial of service through CPU lockup and loss or severe degradation of network processing. No UAF, OOB access, information disclosure, or memory write primitive is supported by the provided code change. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.3 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	REMOTE OOB DEADLOCK DANGER NETWORK HARDWARE BOOT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Firmware-mediated external influence. Rebooting a directly connected peer caused a link or MAC reset during which the NIC exposed the invalid `tpd_cons` value `0xffff`.
* +1 Reliable strong DoS. The unreachable consumer index makes `atl1c_clean_tx()` spin indefinitely, and CPU soft lockups were reproduced on two systems.
* +0 Additional availability. Network degradation and the stuck NAPI thread are consequences of the same infinite loop and are not counted twice.
* +0 Remote reachability. Ordinary routed packets are not shown to produce the invalid hardware register value.
* +0 Memory corruption. The ring index is advanced using the normal wrapping logic. The demonstrated defect is nontermination because it can never equal `0xffff`, not an OOB access.
* +0 Active-state corruption. No attacker-influenced structured state is written or later consumed by a privileged component.
* +0 Authorization impact. No security check, protected resource, or DENY-to-ALLOW transition is involved.
* No hardware penalty was applied. The issue requires affected atl1c hardware, but the supplied evidence does not establish that physical access to the victim or exceptionally rare hardware is required.
* No timing penalty was applied. The bad value occurs during a reset transition, but the condition was reproduced and is not shown to require an uncontrollable narrow race.
* NEW52 B5-R does not apply because there is no confirmed heap OOB write, retry-accumulated offset, or subsequent consumption of corrupted structured state.
* NEW53 B3-PENDING and V32 through V34 do not apply because no checksum metadata or shared-backing write exists.
* NEW54 B4-PENDING does not apply because there is no authorization decision.

3. Reachability analysis

The demonstrated trigger is control over a network device directly connected to the affected atl1c interface. Rebooting or resetting that peer produces a link transition, after which the NIC may return `0xffff` for `tpd_cons`.

No account, UID 0 status, capability, or host-administrator privilege is required on the affected host. The actor does require control of the adjacent peer, so this is not established as an Internet-routable packet attack. No user-namespace or network-namespace capability participates in the demonstrated trigger.

The affected host must use compatible atl1c hardware, with the report specifically identifying Qualcomm Atheros AR8151 v2.0. There is no attacker-created kernel object, sysctl, boot option, or local control-plane prerequisite. Trigger reliability across other atl1c devices remains unresolved.

4. Primitive and severity interpretation

The exact primitive is an infinite kernel loop caused by accepting an impossible hardware consumer index. `next_to_clean` remains ring-bounded while `hw_next_to_clean` is `0xffff`, so the termination condition cannot be reached.

This is CLASS_C invalid-state and DoS behavior. It is not a UAF, OOB read, OOB write, double release, authorization bypass, or active structured-state corruption. The demonstrated consequence is a stuck NAPI thread and CPU soft lockup, with corresponding loss or severe degradation of network processing.

A host-wide panic is not established. There is also no independent integrity primitive or credible path to privilege escalation. Therefore `ImportantCandidate=NO` and automatic downgrade is allowed. Manual review remains recommended to determine whether affected deployments can escalate the single-CPU soft lockup into host-wide unavailability and how reliably an adjacent peer can reproduce it.

5. One-sentence report phrase

An invalid atl1c hardware transmit consumer index can make the NAPI cleanup loop run indefinitely after an adjacent link reset, causing a CPU soft lockup and network denial of service without evidence of memory corruption.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the affected atl1c device range, trigger reliability from an adjacent peer, watchdog recovery behavior, and whether the observed soft lockup remains CPU or interface local.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: atl1c: fix soft lockup on out-of-range tpd_cons read
Commit: e7acd4cdeccbcdfd407adeb72b1eba14d1145b6f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7acd4cdeccbcdfd407adeb72b1eba14d1145b6f

Commit description:

The hardware can report an out-of-range tpd_cons (seen as 0xffff)
while the PCIe link/MAC is resetting. An out-of-range value can
never be reached and the loop below would spin forever. To avoid
a soft lockup treat it as "nothing new to clean" instead.

Reproduced on two machines, same NIC (Qualcomm Atheros AR8151 v2.0,
4-port), triggered by rebooting a Mikrotik CCR2004 PCIe card that
the ports are directly linked to:

- Ubuntu 26.04.1 LTS, kernel 7.0.0-31-generic. The link-flap
  precursor, before the lockup was captured with a full trace
  elsewhere:

    atl1c 0000:05:00.0 enp5s0f0: NETDEV WATCHDOG: CPU: 4: transmit queue 2 timed out 489984 ms
    atl1c 0000:05:00.0: MAC state machine can't be idle since disabled for 10ms second
    atl1c 0000:05:00.0: atl1c: enp5s0f0 NIC Link is Up<65535 Mbps Full Duplex>

  65535 (0xffff) here is the same value tpd_cons reads back once the
  loop below gets stuck.

- Proxmox VE, kernel 7.0.14-11-pve. Same NIC/trigger, this time
  caught by the soft lockup watchdog with a full stack trace:

    watchdog: BUG: soft lockup - CPU#12 stuck for 354s! [napi/eth%d-0:329]
    CPU: 12 UID: 0 PID: 329 Comm: napi/eth%d-0 Tainted: P O L 7.0.14-11-pve #1 PREEMPT(lazy)
    RIP: 0010:atl1c_clean_tx+0x142/0x2d0 [atl1c]
    Call Trace:
     <TASK>
     __napi_poll+0x32/0x1e0
     napi_threaded_poll_loop+0x286/0x2e0
     napi_threaded_poll+0xfd/0x140
     kthread+0xf7/0x130
     ret_from_fork+0x2da/0x3a0
     ret_from_fork_asm+0x1a/0x30
     </TASK>

Fixes: 43250dd ("atl1c: Atheros L1C Gigabit Ethernet driver")
Cc: stable@vger.kernel.org
Signed-off-by: Gajdos Tamás <tamas@rimpianto.com>
Link: https://patch.msgid.link/20260921091334.3571525-2-tamas@rimpianto.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/ethernet/atheros/atl1c/atl1c_main.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=e7acd4cdeccbcdfd407adeb72b1eba14d1145b6f

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

The original Linux kernel CVE announcement for CVE-2026-98489 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98489

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: unknown
  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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).