[CVE-2026-80979][MODERATE 7.0] net/smc: unregister the connection before draining the rx tasklet

[CVE-2026-80979][MODERATE 7.0] net/smc: unregister the connection before draining the rx tasklet

[AL-KERNEL]

CVE: CVE-2026-80979
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/smc: unregister the connection before draining the rx tasklet
Commit: b4d540ac95cd35c6ebab6afb7eae2bcac7b277a5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b4d540ac95cd35c6ebab6afb7eae2bcac7b277a5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80979
Analysis date: Fri, 11 Sep 2026 17:26:37 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
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-2026-80979 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80979

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 7.0
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-2026-80979	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80979 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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in the SMC-D teardown path can leave a freed connection registered in the smcd conn table while device IRQ handling can still re-arm the rx tasklet after tasklet_kill has returned. In the DMB nocopy path the send buffer can be freed after the drain, so the re-armed tasklet may later dereference freed memory and crash the kernel. For the CVSS the PR:N is used because an adjacent SMC-D peer may only need reachability to a service using SMC-D and not a local account on the victim. The attack is not expected to be directly Internet reachable and is mainly relevant to systems using SMC-D over ISM or similar adjacent fabric deployments. Impact is at least denial of service via kernel crash and in the paranoid interpretation may include confidentiality or integrity impact because the bug class is use-after-free in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 6
* Paranoid score: 6
* Applied conservative floor/cap: Real UAF floor 4 applied, 3 -> 4. No paranoid floor/cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / lifetime violation. The commit directly states that a ghost send buffer is freed after the drain and a re-armed rx tasklet can later dereference it.
* +1 Reliable kernel crash / strong DoS. The stale tasklet dereference is a realistic kernel crash path.
* +2 Adjacent network-triggerable exposure. The vulnerable path is in net/smc SMC-D receive/tasklet handling and can be influenced by an SMC-D peer when the target exposes a service using SMC-D.
* -1 Hard timing / teardown interleaving. The bug depends on a specific window between link-group unlinking, deferred connection killing, tasklet draining, and device IRQ re-arming.
* -1 Specialized configuration. The affected path requires SMC-D with ISM and DMB-nocopy support, not a generic TCP/IP Internet-facing path.

Paranoid additional signal:

* +1 Attacker-influenced active-object lifetime / repeatable state. In an exposed SMC-D deployment, a peer can plausibly drive connection activity and teardown attempts while device IRQs can re-arm the tasklet, making the active lifetime race more review-worthy.

Important non-awarded signals:

* +2 Strong exploitation leverage not awarded. Controlled reclaim, attacker-shaped replacement contents, arbitrary kernel read/write, callback control, or demonstrated LPE are not established.
* Structured stale-object leverage not separately awarded. The stale access is meaningful, but no distinct attacker-controlled replacement or post-reuse field consumption is shown.
* Concrete repeated release/refcount +1 not awarded. The patch shows kfree of sndbuf_desc and stale dereference risk, but not a second lifetime/refcount mutation on the exact same dangling reference.
* Paranoid repeated-refcount +1 not awarded. There is no concrete second put/release/refcount operation through freed storage.
* Extra Availability +1 not awarded. The same crash/DoS is already counted once.
* Confidentiality/Integrity points not awarded directly. C/I impact is unresolved and possible only as a paranoid consequence of UAF, not as a demonstrated primitive.

Repeated-release/refcount checklist:

* First release can end lifetime: kfree of sndbuf_desc can free the buffer descriptor.
* Exact same reference survives for second release: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 from repeated release/refcount applied: no.

3. Reachability analysis

The evaluated attacker is an adjacent SMC-D peer rather than a local host administrator. The issue is not expected to be reachable from the public Internet in ordinary deployments, because SMC-D over ISM is normally used in constrained data-center or host-adjacent environments. However, when an SMC-D service is reachable, the peer does not need host-admin privileges on the victim to influence connection activity and receive-side events.

HostAdminRequired is set to NO based on the supplied PR:N hint and the network-facing SMC-D connection context. NamespaceScopedPrivilege is NO because this is not primarily a namespace-created local capability path. Prior setup is required in the operational sense: the target must have SMC-D, an ISM-capable device, and DMB-nocopy support active. That setup is a deployment prerequisite, not an attacker privilege on the victim.

Race repeatability is uncertain. The conservative score penalizes the teardown/IRQ/tasklet timing window. The paranoid score does not apply that penalty because a reachable peer may be able to repeat connection and traffic patterns enough to make the interleaving worth manual review.

4. Primitive and severity interpretation

The exact primitive is a real use-after-free / stale post-lifetime dereference in the SMC-D teardown path. A connection can remain registered in smcd->conn[] after link-group unlinking, leaving smcd_handle_irq() gates open. The device can re-arm the rx tasklet after tasklet_kill() returns, and on the DMB-nocopy path the send buffer descriptor may already have been freed.

This is an active structured lifetime bug, not merely passive metadata corruption. The stale operation occurs in receive tasklet / IRQ-driven processing, not only in a local cleanup helper. At the same time, the patch does not establish controlled reclaim, arbitrary write, callback hijack, or a concrete privilege-escalation chain. Therefore the primitive is CLASS_B rather than CLASS_A.

Demonstrated consequence is kernel crash / DoS. Speculative consequence is broader kernel memory corruption impact if freed memory can be reused in an attacker-useful way, but that is unresolved. ImportantCandidate is YES because this is a network-adjacent active UAF in kernel networking code with unresolved exploitation leverage. AutoDowngradeAllowed is NO because automatically closing it as ordinary DoS would discard a concrete active-object lifetime primitive that requires manual review.

5. One-sentence report phrase

A race in the SMC-D teardown path can leave a connection registered long enough for device IRQ handling to re-arm the rx tasklet after drain, causing a freed DMB-nocopy send buffer to be dereferenced and creating at least an adjacent-network DoS with unresolved UAF exploitation risk.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real race-based UAF in an active network-related tasklet/IRQ path, with adjacent peer reachability and unresolved exploitation leverage beyond the demonstrated crash.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/smc: unregister the connection before draining the rx tasklet
Commit: b4d540ac95cd35c6ebab6afb7eae2bcac7b277a5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b4d540ac95cd35c6ebab6afb7eae2bcac7b277a5

Commit description:

smc_conn_free() calls smc_ism_unset_conn() only while the link group is
still on its device list, and never sets conn->killed.
smc_lgr_terminate_sched() unlinks the group immediately and defers killing
its connections to a work item, so a connection freed in that window keeps
its smcd->conn[] slot with both gates in smcd_handle_irq() open, and the
device can re-arm the receive tasklet after tasklet_kill() has returned. On
the DMB-nocopy path the ghost send buffer is freed right after that drain,
so the re-armed tasklet dereferences it.

Unregister unconditionally and drain before the detach at both teardown
sites, mirroring rmb_desc, which smc_buf_unuse() releases after the drain.
Clear conn->sndbuf_desc before freeing it as well, so a reader that samples
the pointer cannot get one that is already freed.

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-v2-1-61647601a6f3@proton.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/smc/smc_core.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=b4d540ac95cd35c6ebab6afb7eae2bcac7b277a5

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

The original Linux kernel CVE announcement for CVE-2026-80979 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80979

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 4
  Paranoid ActionableScore: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).