[CVE-2026-97946][MODERATE REGULAR] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[CVE-2026-97946][MODERATE REGULAR] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[AL-KERNEL]

CVE: CVE-2026-97946
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: x86/amd_node: Fix PCI device reference counting in amd_smn_init()
Commit: 84e3a71d11d8593c127b468d75b2653af5074f81
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84e3a71d11d8593c127b468d75b2653af5074f81
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97946
Analysis date: Sat, 26 Sep 2026 14:49:36 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97946 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97946

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-2026-97946	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97946 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-911;*CWE-672;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'Incorrect PCI device reference handling in amd_smn_init can store a PCI root device pointer in amd_roots without taking an independent reference. The search iterator later drops its temporary reference, and removal of the PCI device can leave a stale pointer that may be dereferenced by later AMD SMN handling. This is a use after free candidate that can at least cause a kernel crash. For the CVSS the PR:N because the selected physical attack scenario does not require a local user account, but it requires physical PCI device removal or equivalent platform level control. The issue is not network reachable. The base impact is denial of service. The paranoid impact includes confidentiality and integrity because a stale kernel PCI device pointer can be a memory corruption primitive if freed memory can be reused in a controlled manner. This requires manual review of amd_roots users and PCI hot remove exposure.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	INIT SIMPLEFIX HARDWARE DEBUGFS 	YES	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 2
* Paranoid score: 4
* Applied conservative floor: 2 -> 4. A cached PCI device pointer can outlive the temporary iterator reference and is intended for later in-use access.
* Applied paranoid floor: 2 -> 4.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF or lifetime violation. `amd_roots[node]` previously stored `root` without `pci_dev_get(root)`. The subsequent `get_next_root(root)` iterator operation drops the temporary reference to the prior PCI device. If the PCI device is removed and its final reference is dropped, the cached entry can become stale while later AMD SMN code still retains the raw pointer.
* +0 Reliable kernel crash. A stale `struct pci_dev` dereference can plausibly fault, but the supplied patch does not show a crash trace or the later dereference call site.
* +0 Remote reachability. No network-triggerable path is established.
* +0 Local unprivileged trigger. The supplied material does not establish that an ordinary local user can remove the relevant PCI root device or cause the complete stale-use sequence.
* +0 Strong exploitation leverage. Controlled reclaim, object substitution, attacker-controlled post-free fields, arbitrary read or write, callback control, and refcount takeover are not demonstrated.
* +0 Concrete repeated release or refcount mutation. The patch fixes a missing retained reference, not a sequence where the same dangling reference later receives a second `pci_dev_put()` or another lifetime-mutating operation.
* +0 Confidentiality and integrity impact. These are not awarded merely because a stale pointer could theoretically refer to reused memory.
* +0 Hard-race penalty. This is primarily an ownership and reference-lifetime defect, not a demonstrated narrow timing race.
* +0 hardware or physical-only penalty. AMD Zen and PCI topology are relevant conditions, but the supplied evidence does not prove a physical-only attacker model or rare hardware prerequisite for all affected systems.

The prior LLM hint proposing `AV:P` and `C:H/I:H` is not sufficient evidence for ActionableScore escalation. A physical removal scenario and controlled post-free reuse remain plausible hypotheses, but neither is established by the supplied patch.

3. Reachability analysis

The affected code executes during `amd_smn_init()` on AMD Zen systems and caches PCI root devices in the global `amd_roots` array. The vulnerable lifetime sequence requires a cached PCI root device to later lose its PCI-core lifetime protection while code can still use the cached entry.

The supplied patch does not establish who can complete that sequence. Possible conditions include PCI hot removal, platform-level device removal, driver-mediated removal, or another PCI-device lifecycle transition. However, the patch does not prove that an ordinary local user, a namespaced user, a delegated service, or a host administrator can reliably trigger the complete sequence.

HostAdminRequired is therefore `UNKNOWN`, not `YES` and not `NO`. NamespaceScopedPrivilege is also `UNKNOWN`. No relevant namespace-aware capability check or complete namespace-scoped trigger path is supplied. No network exposure, prior privileged setup requirement, boot parameter requirement, or attacker-controlled PCI device provisioning is established by the provided context.

4. Primitive and severity interpretation

The exact primitive is a stale cached `struct pci_dev` pointer caused by failure to take an independent `pci_dev_get()` reference before storing the pointer in `amd_roots`. The iterator owns only a temporary search reference and releases the previous iterator object when advancing.

This is an active structured-object lifetime issue, not a fixed async buffer case. However, the supplied diff does not show a post-free dereference site, object replacement, attacker-shaped reuse, callback dispatch, or a second lifetime-mutating operation through the stale pointer. It therefore remains `CLASS_B`, not `CLASS_A`.

The demonstrated defect is a missing ownership reference that can permit a stale pointer after device removal. The likely direct consequence is a kernel fault or DoS if later AMD SMN handling dereferences the stale entry. A confidentiality, integrity, or privilege-escalation consequence is speculative because controlled post-free reuse and attacker influence over the reused object are not established.

ImportantCandidate is `NO` because this is currently a constrained lifetime UAF candidate with unresolved reachability and no demonstrated exploitation leverage beyond a possible stale dereference. AutoDowngradeAllowed is `YES` because no concrete repeated refcount mutation, controlled reclaim, security-boundary bypass, disclosure primitive, or directed corruption mechanism is established. Manual review remains recommended to inspect all `amd_roots` consumers and determine whether PCI root removal can occur before those consumers run.

5. One-sentence report phrase

A missing `pci_dev_get()` when caching AMD PCI root devices can leave stale `amd_roots` entries after device removal, potentially causing a later kernel use-after-free dereference and denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review later `amd_roots` dereference sites and PCI root-device removal paths to determine whether a stale cached `struct pci_dev` can be reached by a realistic attacker and whether any post-free structured-object processing occurs.

7. Call-site confidence

Call-site confidence: medium

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

Patch: x86/amd_node: Fix PCI device reference counting in amd_smn_init()
Commit: 84e3a71d11d8593c127b468d75b2653af5074f81
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84e3a71d11d8593c127b468d75b2653af5074f81

Commit description:

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kernel/amd_node.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=84e3a71d11d8593c127b468d75b2653af5074f81

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

The original Linux kernel CVE announcement for CVE-2026-97946 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97946

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:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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).