[CVE-2026-63890][MODERATE REGULAR] scsi: fcoe: Reject FIP descriptors with zero fip_dlen in CVL walker

[CVE-2026-63890][MODERATE REGULAR] scsi: fcoe: Reject FIP descriptors with zero fip_dlen in CVL walker

[AL-KERNEL]

CVE: CVE-2026-63890
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: scsi: fcoe: Reject FIP descriptors with zero fip_dlen in CVL walker
Commit: d179949d2175d2857d1c3a275a22bea58bcc5d36
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d179949d2175d2857d1c3a275a22bea58bcc5d36
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63890
Analysis date: Sun, 19 Jul 2026 11:59:46 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / Actionable Moderate candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-63890 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63890

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-63890	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;*CWE-20;**CWE-400;BEST CVSS score: '6.5';DESCR 'A malformed FIP CVL frame can make the FCoE controller CVL descriptor walker loop forever because a non critical descriptor with fip_dlen 0 advances the descriptor cursor by zero bytes. An unauthenticated L2 peer on the FCoE control VLAN can trigger this against affected fcoe, qedf, or bnx2fc initiators by sending a crafted FIP frame. For the CVSS the PR:N is used because no victim side account or local code execution is needed once the attacker can transmit on the adjacent FCoE control network. The issue is adjacent network reachable rather than Internet remote, so AV:A is used. Impact is denial of service because FIP receive work can be blocked indefinitely and later FIP frames for that controller may not be processed. No memory corruption, information disclosure, or privilege escalation primitive is indicated by the code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / Actionable Moderate candidate (with actual score 4)	YES	LOCK HARDWARE  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / Actionable Moderate candidate**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. The trigger is an unauthenticated FIP frame from an L2 peer on the FCoE control VLAN. This is not Internet remote, but it is realistically network-triggerable on the adjacent storage network.
* Reliable kernel crash / strong DoS: +1. The zero-length descriptor causes the CVL walker to make no progress and can hang fcoe_ctlr_recv_work indefinitely.
* Important filesystem/storage path: +1. FCoE is a storage transport path, and blocking FIP processing can affect discovery, keep-alive, recovery, and storage availability.
* Rare AND difficult-to-reach subsystem/configuration: -1. FCoE deployments are specialized and normally limited to storage VLANs rather than broad default exposure.
* Availability impact realistic: +1. The impact can persist for the affected controller worker and block subsequent FIP frames, extending beyond a transient warning.
* No memory corruption bonus. The patch shows an input-validation fix for an infinite loop, not UAF, OOB write, double-free, type confusion, or refcount corruption.
* No privilege escalation bonus. No LPE primitive is supported by the patch or described behavior.
* No confidentiality or integrity impact. The demonstrated impact is availability only.

3. Reachability analysis
An unauthenticated host that can transmit FIP frames on the same FCoE control VLAN can trigger the issue. No local account on the victim is required, so the practical PR is none once adjacent L2 network access exists. Namespaces and containers do not materially lower the requirement unless they can send raw Ethernet traffic onto the FCoE VLAN, which is not typical. The affected path is only present on systems using FCoE initiators such as fcoe, qedf, or bnx2fc, so exposure is specialized but realistic in storage networks.

4. Severity interpretation
This behaves like an actionable Moderate availability issue, not an Important memory-corruption issue. The theoretical risk is limited because the bug is an infinite-loop/progress bug in descriptor walking and does not show stale object reuse, attacker-controlled overwrite, or privileged data exposure. The realistic impact is stronger than ordinary local Moderate because the trigger is unauthenticated on an adjacent storage control network and can block FIP processing for the controller.

5. One-sentence report phrase
A malformed FIP CVL descriptor with zero fip_dlen can cause the FCoE CVL walker to loop indefinitely, allowing an unauthenticated adjacent L2 peer on the FCoE control VLAN to block FIP processing and cause storage-path denial of service.

6. Manual review recommendation
MANUAL CHECK REQUIRED.
Reason: the issue is unauthenticated and network-triggerable on an adjacent storage control network, with reliable availability impact, even though there is no supported memory-corruption or privilege-escalation primitive.

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

Patch: scsi: fcoe: Reject FIP descriptors with zero fip_dlen in CVL walker
Commit: d179949d2175d2857d1c3a275a22bea58bcc5d36
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d179949d2175d2857d1c3a275a22bea58bcc5d36

Commit description:

drivers/scsi/fcoe/fcoe_ctlr.c::fcoe_ctlr_recv_clr_vlink() advanced the
descriptor cursor by an attacker-supplied fip_dlen without ever
requiring dlen >= sizeof(struct fip_desc) in the default branch.  The
named descriptor cases (FIP_DT_MAC, FIP_DT_NAME, FIP_DT_VN_ID) checked
their per-type minimum lengths, but a FIP_DT_NON_CRITICAL descriptor
(fip_dtype >= 128, which the standard requires receivers to silently
ignore) skipped that check entirely.

An unauthenticated L2 peer on the FCoE control VLAN could hang
fcoe_ctlr_recv_work on an fcoe, qedf, or bnx2fc initiator indefinitely
by emitting one FIP CVL frame whose single descriptor had fip_dtype ==
FIP_DT_NON_CRITICAL and fip_dlen == 0: the cursor advanced zero bytes
per iteration and the loop condition rlen >= sizeof(*desc) stayed true
forever, blocking every subsequent FIP frame on that controller.

Tighten the outer dlen guard to also reject dlen < sizeof(struct
fip_desc), so a malformed descriptor whose length cannot even cover the
descriptor header is rejected before the switch.  This is the same
lower-bound the named cases already apply and is the minimum scope that
closes the loop.

Fixes: 97c8389 ("[SCSI] fcoe, libfcoe: Add support for FIP. FCoE discovery and keep-alive.")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Link: https://patch.msgid.link/20260518144307.2820961-1-michael.bommarito@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/scsi/fcoe/fcoe_ctlr.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=d179949d2175d2857d1c3a275a22bea58bcc5d36

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

The original Linux kernel CVE announcement for CVE-2026-63890 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63890

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: Not available
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: unknown
  Paranoid ActionableScore: 4

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).