[CVE-2026-80981][MODERATE 7.0] net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()

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

CVE: CVE-2026-80981
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()
Commit: c52a998a223e7e84333306996edec096178d1e95
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c52a998a223e7e84333306996edec096178d1e95
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80981
Analysis date: Fri, 11 Sep 2026 18:27:33 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80981 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80981

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-2026-80981	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80981 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-825;CWE-125;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 use-after-free in the SMC LLC add link server path occurs because add_llc points into an LLC queue entry that can be freed before smc_llc_save_add_link_rkeys reads from it. A remote SMC peer on the same SMC/RDMA or rxe capable network may be able to trigger the vulnerable add link flow when SMC-R V2 is used and the connection does not use a shared v2 receive buffer. For the CVSS the PR:N is used because the attacker does not need a local account on the victim and only needs protocol reachability to the exposed SMC service in the relevant fabric. The attack complexity is high because exploitation depends on a specific SMC-R configuration and link negotiation state. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because the bug is a real UAF read from a freed kmalloc object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	READ OOB DANGER UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the conservative score. No floor or cap changed the paranoid score.

2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / active lifetime violation: `add_llc` points inside `qentry`, `smc_llc_flow_qentry_del()` frees `qentry`, and the stale pointer is later passed to `smc_llc_save_add_link_rkeys()`.
* +1 Reliable kernel crash / strong DoS: KASAN shows `slab-use-after-free` in `smc_llc_save_add_link_rkeys()`, and the path is in kernel workqueue context.
* +2 Network or fabric reachable protocol path: the vulnerable SMC LLC add-link flow is reachable from an SMC peer over an SMC/RDMA or rxe-capable environment, without requiring a local account on the victim.

Conservative negative signals:

* No negative privilege penalty: host-admin-equivalent privilege is not required by the attacker in the supplied attacker model.
* No race penalty: this is an ordered lifetime error in one flow, not a narrow timing race.
* No rare-hardware penalty: RDMA or rxe-capable SMC-R deployment is a material condition, but rxe indicates this is not strictly physical-only rare hardware.

Paranoid additional signal:

* +1 Structured stale-object exploitation leverage: the stale pointer references an LLC queue message object containing protocol fields, and the later stale read feeds `smc_llc_save_add_link_rkeys()`, which processes link/rkey information used in SMC-R setup. This is more than a trivial cleanup-only dereference, but controlled reclaim or arbitrary write is not demonstrated.

Important non-awarded signals:

* Strong LPE / strong exploitation leverage +2 not awarded: no controlled reclaim, object replacement, arbitrary kernel R/W, callback control, credential manipulation, or demonstrated privilege escalation is established.
* Concrete repeated release/refcount +1 not awarded: the bug is a free followed by stale read, not a second lifetime/refcount mutation through the same dangling reference.
* Paranoid repeated-refcount leverage +1 not awarded: no second `put`, `release`, `free`, or refcount decrement on the exact same freed object is shown.
* Confidentiality +1 not awarded independently: the UAF read is internal to kernel processing and no user/network disclosure path is demonstrated.
* Integrity +1 not awarded independently: rkey/link state use is concerning, but unauthorized modification of protected state is not concretely established.
* Extra Availability +1 not awarded: the same KASAN/Oops/crash is already counted as Reliable kernel crash / strong DoS.
* Remote Internet exposure bonus not added: SMC-R is normally a fabric/datacenter style protocol path, not a public Internet service.

Repeated-release checklist:

* First release can end lifetime: yes, `smc_llc_flow_qentry_del()` kfree()s the queue entry.
* Exact same reference survives: yes, `add_llc` remains pointing inside the freed `qentry`.
* Second operation is lifetime/refcount mutation: no, the later operation is a stale read/use in `smc_llc_save_add_link_rkeys()`.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: not needed. Conservative arithmetic already reaches 5.

3. Reachability analysis

The evaluated attacker is a remote or adjacent SMC peer, not a local user on the victim. The vulnerable path is in the SMC LLC server add-link handling flow and is exercised during SMC-R V2 link negotiation. The supplied reproduction uses rxe and a forced `max_recv_sge == 1`, and the vulnerable branch requires no shared v2 receive buffer.

Host administrator privilege is not required for the attacker once the victim exposes the relevant SMC service and SMC/RDMA or rxe environment. Therefore `HostAdminRequired=NO`. This is not a namespace-scoped privilege case, so `NamespaceScopedPrivilege=NO`.

Prior system setup is relevant operationally: the victim must support and use SMC-R V2 with a suitable RDMA or rxe configuration. That affects real-world exposure, but it is not a reason to treat the attacker as host-admin. The issue is not a generic Internet TCP bug, but it is protocol/fabric reachable from an SMC peer in the relevant environment.

No hard race is required. The core bug is deterministic lifetime ordering: free the queue entry, keep a pointer into it, then read through that pointer later in the same function flow.

4. Primitive and severity interpretation

The exact primitive is a real slab use-after-free read. `add_llc` points into an LLC queue entry. The entry is freed by `smc_llc_flow_qentry_del()`. Later, when there is no shared v2 receive buffer, the stale `add_llc` pointer is used as `llc_msg` and read by `smc_llc_save_add_link_rkeys()`.

This is an active structured object, not fixed stale storage. The stale data is an SMC LLC message structure used for link setup and rkey processing. The demonstrated consequence is a kernel KASAN UAF report and likely kernel crash or DoS. The speculative consequence is stronger exploitation through stale structured message processing, especially if reuse can be influenced between free and read, but controlled reclaim is not established.

This is not an ordinary repeated-release bug. It is category A under the prompt distinction for stale read/use, not category B second lifetime/refcount mutation. There is no second `free` or `put` on the same dangling reference in the shown patch.

Primitive class is `CLASS_B` because a concrete kernel lifetime violation exists, but no Class A primitive such as controlled reclaim, arbitrary write, callback control, or demonstrated LPE is shown. `ImportantCandidate=YES` because the bug is a network/fabric reachable real UAF in active protocol state and the exploitation leverage beyond crash is unresolved. `AutoDowngradeAllowed=NO` because automatically closing it as ordinary Moderate would discard a meaningful unresolved lifetime-corruption primitive in a network-adjacent SMC path.

Likely operational severity is Actionable Moderate at minimum, with Strong Important review warranted if further analysis shows controllable reclaim, stable post-free replacement, useful corruption of link/rkey state, or a practical crash trigger from an unauthenticated SMC peer.

5. One-sentence report phrase

A use-after-free in `smc_llc_srv_add_link()` lets an SMC/RDMA or rxe peer reach a stale LLC queue-entry read during SMC-R V2 add-link handling, causing kernel DoS and requiring manual review because active protocol state is consumed after free.

6. Manual review recommendation

MANUAL CHECK REQUIRED

A real UAF is confirmed, the path is reachable through SMC protocol handling, and the stale read feeds nontrivial SMC-R link/rkey processing. Controlled reclaim or privilege escalation is not demonstrated, but automatic downgrade is not safe.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()
Commit: c52a998a223e7e84333306996edec096178d1e95
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c52a998a223e7e84333306996edec096178d1e95

Commit description:

smc_llc_srv_add_link() keeps add_llc pointing into the queue entry:

  add_llc = &qentry->msg.add_link;			smc_llc.c:1482
  ...
  smc_llc_save_add_link_info(link_new, add_llc);	smc_llc.c:1494
  smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);		smc_llc.c:1495
  ...
  u8 *llc_msg = smc_link_shared_v2_rxbuf(link) ?
	(u8 *)lgr->wr_rx_buf_v2 : (u8 *)add_llc;	smc_llc.c:1504
  smc_llc_save_add_link_rkeys(link, link_new, llc_msg);	smc_llc.c:1506

smc_llc_flow_qentry_del() kfree()s the entry, so on a link without a shared
v2 receive buffer the pointer handed to smc_llc_save_add_link_rkeys() is
already freed. Before the Fixes: commit that branch always used
lgr->wr_rx_buf_v2 and add_llc was not used after the free.

Reproduced on an unpatched tree over rxe, with KASAN, kasan_multi_shot
and a link forced to max_recv_sge == 1: the entry is freed and read by
the same call, and the freeing frame is smc_llc_srv_add_link() itself.

  [    2.523161] BUG: KASAN: slab-use-after-free in smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523499] Read of size 2 at addr ffff8880052194de by task kworker/0:1/11
  [    2.523789]
  [    2.523862] CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 7.2.0-rc5-p0-g2c9dd296545d #35 PREEMPT(lazy)
  [    2.523865] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
  [    2.523866] Workqueue: smc_hs_wq smc_listen_work
  [    2.523869] Call Trace:
  [    2.523870]  <TASK>
  [    2.523871]  dump_stack_lvl+0x53/0x70
  [    2.523872]  print_report+0xd0/0x630
  [    2.523874]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
  [    2.523876]  ? smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523878]  kasan_report+0xce/0x100
  [    2.523879]  ? smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523881]  smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523883]  ? smcr_buf_reg_lgr+0x2a4/0x660
  [    2.523885]  smc_llc_srv_add_link+0xaa2/0x1e50
  [    2.523888]  ? _printk+0xba/0xf0
  [    2.523897]  ? __pfx_smc_llc_srv_add_link+0x10/0x10
  [    2.523899]  ? down_write+0xb0/0x130
  [    2.523903]  ? __pfx_down_write+0x10/0x10
  [    2.523905]  smc_listen_work+0x489e/0x4d00
  [    2.523907]  ? kmem_cache_free+0x1c6/0x3a0
  [    2.523911]  ? __pfx_smc_listen_work+0x10/0x10
  [    2.523913]  ? release_sock+0x148/0x1d0
  [    2.523915]  ? smc_tcp_listen_work+0xb4f/0xfc0
  [    2.523917]  ? _raw_spin_lock_irq+0x80/0xe0
  [    2.523918]  ? __pfx__raw_spin_lock_irq+0x10/0x10
  [    2.523920]  process_one_work+0x633/0x1030
  [    2.523922]  ? assign_work+0x11d/0x370
  [    2.523924]  worker_thread+0x45b/0xd10
  [    2.523926]  ? __pfx_worker_thread+0x10/0x10
  [    2.523928]  ? __pfx_worker_thread+0x10/0x10
  [    2.523929]  kthread+0x2c6/0x3b0
  [    2.523931]  ? recalc_sigpending+0x15c/0x1e0
  [    2.523934]  ? __pfx_kthread+0x10/0x10
  [    2.523935]  ret_from_fork+0x36e/0x5a0
  [    2.523937]  ? __pfx_ret_from_fork+0x10/0x10
  [    2.523938]  ? __switch_to+0x572/0xdd0
  [    2.523943]  ? __pfx_kthread+0x10/0x10
  [    2.523944]  ret_from_fork_asm+0x1a/0x30
  [    2.523947]  </TASK>
  [    2.523948]
  [    2.531253] Allocated by task 48:
  [    2.531399]  kasan_save_stack+0x33/0x60
  [    2.531570]  kasan_save_track+0x14/0x30
  [    2.531737]  __kasan_kmalloc+0x8f/0xa0
  [    2.531905]  __kmalloc_cache_noprof+0x158/0x370
  [    2.532100]  smc_llc_enqueue+0x72/0x560
  [    2.532268]  smc_wr_rx_tasklet_fn+0x474/0xa80
  [    2.532491]  tasklet_action_common+0x20f/0x8a0
  [    2.532714]  handle_softirqs+0x18e/0x590
  [    2.532886]  do_softirq+0x3b/0x60
  [    2.533036]  __local_bh_enable_ip+0x61/0x70
  [    2.533221]  __alloc_skb+0x732/0x890
  [    2.533384]  rxe_init_packet+0x16b/0x4f0
  [    2.533567]  prepare_ack_packet+0xb8/0x830
  [    2.533760]  rxe_receiver+0x495/0x96e0
  [    2.533933]  do_work+0x144/0x470
  [    2.534078]  process_one_work+0x633/0x1030

[Commit description truncated; see the upstream URL below]

Changed files:
  net/smc/smc_llc.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=c52a998a223e7e84333306996edec096178d1e95

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

The original Linux kernel CVE announcement for CVE-2026-80981 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80981

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: 5
  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).