[CVE-2026-90421][MODERATE REGULAR] PCI: Fix UAF when probe runs concurrent to dyn ID removal [ Upstream

[CVE-2026-90421][MODERATE REGULAR] PCI: Fix UAF when probe runs concurrent to dyn ID removal [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90421
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: PCI: Fix UAF when probe runs concurrent to dyn ID removal [ Upstream
Commit: 42a5661ff7e4c7d3c5025d0f8e5079fb5479ea49
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42a5661ff7e4c7d3c5025d0f8e5079fb5479ea49
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90421
Analysis date: Thu, 17 Sep 2026 17:21:46 -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.

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

The original Linux kernel CVE announcement for CVE-2026-90421 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90421

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-2026-90421	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90421 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-367;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the PCI dynamic ID matching path can return a pointer to dynid id after dynids.lock is released while remove_id_store can concurrently remove and free the same dynamic ID node. A following probe may pass this stale pci_device_id pointer to the driver probe callback, so the driver can read freed memory and act on corrupted or reused id fields. For the CVSS the PR:L is used in the paranoid score because reliable triggering needs local code or a local management context, but delegated driver sysfs access or reduced capability root should not be treated as full PR:H for manual-review sensitivity. The issue is not network reachable and is triggered through local PCI driver dynamic ID management. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free in a core driver binding path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	LOCK UAF HARDWARE LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

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

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation: `pci_match_device()` could return a pointer to `dynid->id`, but `remove_id_store()` may free the containing dynamic ID after `dynids.lock` is released.
* +1 Reliable kernel crash / strong DoS: a later probe path may pass the stale `pci_device_id` pointer to driver probe code, creating a realistic stale dereference / kernel fault risk.
* +1 Attacker-influenced repeatable lifetime manipulation: the same administrative actor can add/remove dynamic IDs and provoke matching/probing repeatedly, affecting the lifetime transition relevant to the stale pointer.
* -2 Host-admin-equivalent privilege: PCI dynamic ID management through sysfs `new_id` / `remove_id` is normally host-root / host-admin controlled and not namespace scoped.

Paranoid additional signal:

* +1 Structured stale-object exploitation leverage: `pci_device_id` is an active structured object consumed by driver matching/probe logic, and fields such as match values and `driver_data` may influence probe behavior. This is enough for a cautious extra review point, but not enough for Class A.

Important non-awarded signals:

* Strong LPE +2 not awarded: no controlled reclaim, attacker-shaped replacement object, arbitrary write, callback control, or demonstrated privilege escalation is established.
* Confidentiality / integrity bonuses not awarded: C/I impact is possible only as a speculative consequence of UAF reuse, not directly shown.
* Concrete repeated release/refcount +1 not awarded: the stale pointer is passed/read by probe logic, but the patch does not show a second `put` / `release` / refcount mutation on the same dangling reference.
* Extra Availability not awarded: the same potential crash is already counted once.
* Remote reachability not awarded: this is local PCI driver sysfs control-plane behavior, not packet or network input.
* Race penalty not applied: although the bug is a race, the administrative actor can plausibly retry add/remove/probe operations. The patch does not establish a rare one-shot timing window.

Repeated-release/refcount checklist:

* First release can end lifetime: yes, `remove_id_store()` can free the dynamic ID node.
* Exact same reference survives: yes, old code could keep `&dynid->id` after dropping `dynids.lock`.
* Second operation is lifetime/refcount mutation: no, the later operation is probe consumption of the stale ID pointer.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no, because there is no concrete second lifetime/refcount mutation and host-admin-equivalent privilege is established.

3. Reachability analysis

The trigger requires manipulating PCI driver dynamic IDs through sysfs, specifically adding/removing IDs and racing that against PCI driver matching/probe. These sysfs controls are normally writable only by host root or an equivalent host administrator. The complete trigger is not known to be available inside attacker-created namespaces, and PCI physical device/driver binding is not generally namespace scoped.

There is no direct network vector. There is no ordinary local unprivileged path established by the supplied evidence. A delegated device-management service or misconfigured sysfs permissions could reduce the practical privilege requirement in a specific product, but that is not established by the patch itself.

Prior host setup is effectively required in the sense that the attacker must have access to PCI driver dynamic ID management. No rare hardware penalty is applied because PCI is common, but the vulnerable interface is administrative control-plane functionality rather than a broadly exposed data-plane API.

The bug is a concurrency issue between probe/match and dynamic ID removal. The race is real, but repeated attempts appear feasible for an actor who can manage dynamic IDs, so no hard-race penalty is applied.

4. Primitive and severity interpretation

The exact primitive is a real stale pointer / use-after-free of a `pci_device_id` embedded in a dynamic PCI ID node. The stale object is an active structured object, not fixed stale storage, because its fields are consumed by PCI driver matching and probe behavior. The demonstrated consequence is kernel instability or crash when driver probe code receives or reads a freed ID object.

This is not merely an ordinary stale cleanup dereference, but it also is not a concrete repeated lifetime/refcount mutation. The first lifetime operation is freeing the dynamic ID node. The second operation is structured consumption of the stale `pci_device_id`, not a second `put` or `free`.

PrimitiveClass is CLASS_B. The bug establishes a real kernel lifetime violation, but not a Class A primitive such as controlled reclaim, arbitrary write, callback hijack, demonstrated LPE, or security-boundary bypass.

ImportantCandidate is NO because the complete established trigger is host-admin-equivalent and no below-host-admin exploitation path or strong post-free exploitation primitive is demonstrated. AutoDowngradeAllowed is YES for generic triage because this is a host-admin-gated Class B UAF with crash/DoS as the concrete demonstrated consequence, although manual review is still recommended if the product delegates PCI driver sysfs management.

Likely operational severity: borderline to actionable Moderate in generic kernel triage, higher only for environments where dynamic PCI ID management is delegated below host admin.

5. One-sentence report phrase

A race between PCI dynamic ID matching and sysfs dynamic ID removal can leave probe code using a freed `pci_device_id`, causing a local host-admin-triggered UAF with likely kernel crash impact and no established remote or unprivileged path.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real core PCI UAF involving an active structured object passed into driver probe callbacks, but the established trigger appears host-admin-gated and no controlled reclaim, arbitrary write, or below-host-admin privilege escalation path is shown.

7. Call-site confidence

Call-site confidence: high

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

Patch: PCI: Fix UAF when probe runs concurrent to dyn ID removal [ Upstream
Commit: 42a5661ff7e4c7d3c5025d0f8e5079fb5479ea49
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42a5661ff7e4c7d3c5025d0f8e5079fb5479ea49

Changed files:
  drivers/pci/pci-driver.c
  include/linux/pci.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=42a5661ff7e4c7d3c5025d0f8e5079fb5479ea49

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

The original Linux kernel CVE announcement for CVE-2026-90421 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90421

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:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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).