[CVE-2026-80984][MODERATE REGULAR] net/smc: do not dereference an unset send buffer on the SMC-D teardown path

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

CVE: CVE-2026-80984
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/smc: do not dereference an unset send buffer on the SMC-D teardown path
Commit: e3fcff8d22a6c9540748846cd800443a643553a6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3fcff8d22a6c9540748846cd800443a643553a6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80984
Analysis date: Fri, 11 Sep 2026 18:49:37 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
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-2026-80984 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80984

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-2026-80984	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80984 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-476;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'SMC-D teardown can hit a NULL pointer dereference because smc_close_stream_wait calls smc_tx_prepared_sends while sk_wait_event may evaluate the condition with the socket lock released. During link group termination smcd_buf_detach can clear conn sndbuf_desc, leaving the close path or SIOCOUTQ path to read an unset send buffer descriptor. For the CVSS the PR:N is used in the paranoid adjacent interpretation because an SMC peer may be able to influence link group teardown without local privileges on the victim, while the base local interpretation uses PR:L for a local process that owns an SMC socket. The issue is not Internet remote in the normal sense and is limited to SMC capable environments, especially SMC-D deployments. Impact is denial of service via kernel fault during close or ioctl. There is no concrete evidence of an information leak, arbitrary write, or privilege escalation primitive from this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DANGER SIMPLEFIX LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +1 Reliable kernel crash / strong DoS. The patch and commit describe a NULL pointer dereference faulting out of close or ioctl when conn->sndbuf_desc is unset.
* +1 Local below-host-admin trigger. A local process can own and close an SMC socket or issue SIOCOUTQ once the SMC environment is available.
* 0 Race penalty not applied. Although this is a race, the supplied evidence does not prove a one-shot or practically non-repeatable timing window.

Paranoid signals:

* +1 Reliable kernel crash / strong DoS. Same demonstrated NULL dereference.
* +2 Adjacent / peer-influenced reachability. In the stronger interpretation, an SMC peer or adjacent SMC-D environment may influence link group teardown while the victim socket is waiting.

Non-awarded signals:

* RealUAF not awarded. The supplied patch establishes an unset NULL sndbuf_desc dereference, not a stale freed object use.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded.
* Strong LPE or weak LPE not awarded.
* Concrete repeated release/refcount not present.
* Structured stale-object leverage not awarded because the stale operation is a NULL descriptor read/deref, not meaningful post-free structured processing.
* Extra availability not awarded because the same kernel fault is already counted.
* Direct Internet remote reachability not established.

Repeated-release/refcount checks:

* First release can end lifetime: not established.
* Exact same reference survives to a second lifetime mutation: not established.
* Second lifetime/refcount mutation: not present.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The realistic trigger is a local process using an SMC socket while SMC-D teardown or link group termination clears conn->sndbuf_desc. The local socket close path calls smc_close_stream_wait, which calls smc_tx_prepared_sends inside a wait condition that may be evaluated with the socket lock released. The ioctl path also reads sndbuf_desc.

Host administrator privilege is not positively required for the socket close or ioctl operation itself, so HostAdminRequired is NO. The environment still requires SMC-D support and suitable setup, but that is treated as deployment exposure rather than a proven host-admin trigger requirement.

Namespace-scoped privilege is not the relevant model here. No complete namespace capability chain is established or needed.

The paranoid reachability model is adjacent rather than Internet remote. An SMC peer may be able to influence link group termination, but the supplied evidence does not prove a pure unauthenticated remote packet-to-crash path.

Race repeatability is uncertain but not proven to be so narrow that a negative timing penalty should be applied.

4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference of conn->sndbuf_desc after teardown clears the send buffer descriptor. This is Class C invalid-state crash behavior, not a real UAF.

The affected object is a structured SMC connection, but the consumed field is simply an unset descriptor pointer. The patch does not show controlled object reuse, attacker-shaped replacement contents, callback use, arbitrary read/write, or refcount corruption.

Demonstrated consequence is denial of service through kernel fault during close or ioctl. Speculative consequences beyond DoS are not supported by the patch. ImportantCandidate is NO because no meaningful exploitation leverage beyond crash is established. AutoDowngradeAllowed is YES because this is constrained crash-only behavior without UAF, repeated lifetime mutation, authorization bypass, or controlled corruption.

Likely operational severity is ordinary to borderline Moderate, with manual review recommended mainly due to network-adjacent SMC-D teardown semantics and the note that a companion patch handles the receive tasklet path.

5. One-sentence report phrase

An SMC-D teardown race can clear conn->sndbuf_desc while close or SIOCOUTQ still reads it, causing a NULL pointer dereference and kernel DoS in SMC capable environments.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the demonstrated primitive is crash-only, but SMC-D peer influence and the dependency on the companion receive-tasklet fix should be checked before automatic closure.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/smc: do not dereference an unset send buffer on the SMC-D teardown path
Commit: e3fcff8d22a6c9540748846cd800443a643553a6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3fcff8d22a6c9540748846cd800443a643553a6

Commit description:

smc_close_stream_wait() calls smc_tx_prepared_sends() from inside its
sk_wait_event() condition, and sk_wait_event() evaluates that condition
once with the socket lock released. smcd_buf_detach() clears
conn->sndbuf_desc from smc_conn_kill() under lock_sock(), so a link group
terminating while a socket waits there leaves the helper dereferencing
NULL, faulting out of close(). SIOCOUTQ reads the field by hand, and
smc_close_cancel_work() drops the lock across two cancel_*_sync() calls.

Sample the pointer once in the helper, report nothing prepared while it is
unset, and bound the ioctl the same way. The receive tasklet dereferences
the field directly in smc_cdc_msg_recv_action(), not through this helper;
1/2 is what keeps it from running that late.

Fixes: ae2be35 ("net/smc: {at|de}tach sndbuf to peer DMB if supported")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
Link: https://patch.msgid.link/20260808-b4-disp-22f119e6-v2-2-61647601a6f3@proton.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/smc/af_smc.c
  net/smc/smc_tx.h

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=e3fcff8d22a6c9540748846cd800443a643553a6

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

The original Linux kernel CVE announcement for CVE-2026-80984 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80984

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:H
  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: 2
  Paranoid ActionableScore: 3

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).