[CVE-2026-90001][MODERATE 7.0] HID: bpf: serialize device reference release in struct_ops destroy path

[CVE-2026-90001][MODERATE 7.0] HID: bpf: serialize device reference release in struct_ops destroy path

[AL-KERNEL]

CVE: CVE-2026-90001
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: HID: bpf: serialize device reference release in struct_ops destroy path
Commit: 401359684620145be710de97b87e1a47abfe1459
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=401359684620145be710de97b87e1a47abfe1459
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90001
Analysis date: Wed, 16 Sep 2026 08:50:32 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
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-2026-90001 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90001

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-2026-90001	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90001 CHECK WITH IMPACT FROM ORIG NN LOW	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-415;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the HID BPF struct_ops destroy path can allow __hid_bpf_ops_destroy_device and hid_bpf_unreg to release the same hid_device registration reference. This can double put struct hid_device and free it while hid_destroy_device is still using the object, creating a kernel use after free condition. For the CVSS the PR:L is used because exploitation requires local code able to interact with HID BPF or a process holding the needed BPF related capability, but it does not necessarily require full unrestricted root in practical deployments. The issue is not network reachable and depends on racing BPF link or map release with HID device teardown. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel UAF memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	LOCK USB BPF RACE UAF HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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

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

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

Applied conservative floor: 4 -> 5. The REAL UAF FLOOR 5 applies because the patch establishes a concrete repeated release/refcount operation on the same registration reference after an earlier release may end the object lifetime.

2. Signal breakdown

Positive conservative signals:

* +2 Real UAF / active lifetime violation: `hid_bpf_unreg()` and `__hid_bpf_ops_destroy_device()` can race on the same HID-BPF registration reference. The same `struct hid_device` reference can be put twice, and the object can be freed while `hid_destroy_device()` still uses it.
* +1 Concrete repeated release/refcount operation: each successful attach takes one `hid_get_device()` reference, and both destroy and unreg paths can perform `hid_put_device()` for the same registration reference. The first put can end lifetime, and the exact same reference can reach a second lifetime-mutating put.
* +1 Reliable kernel crash / strong DoS: the commit states that the device can be freed while teardown is still using it, causing subsequent teardown to touch freed memory.

Positive paranoid-only signal:

* +1 Paranoid repeated-refcount leverage: awarded in raw paranoid scoring because the second `hid_put_device()` is a real write-like lifetime/refcount mutation through storage whose original `hid_device` lifetime may already have ended. This is not arbitrary write or controlled reclaim, but it is stronger than a shallow stale dereference.

Non-awarded or withheld signals:

* +0 Controlled reclaim not demonstrated: no evidence that attacker can place a controlled replacement object at the freed `hid_device` address.
* +0 Arbitrary read/write not demonstrated: no directed kernel read/write primitive is shown.
* +0 Structured stale-object leverage not separately awarded: the meaningful structured operation is the second lifetime/refcount mutation and is already counted under the concrete repeated release/refcount rule.
* +0 Weak LPE not separately awarded: same repeated-release fact is not double-counted as Weak LPE.
* +0 Confidentiality and integrity bonuses not awarded: C/I impact is not established by the patch beyond unresolved UAF corruption risk.
* +0 Extra availability not awarded: the crash/DoS effect is already counted once.
* +0 Remote reachability not established: the issue is local HID-BPF control path, not packet/network triggered.
* +0 Race timing penalty not applied: although this is a race, the supplied evidence shows a concrete TOCTOU between two reachable release paths rather than proving an unusually narrow or externally uncontrollable one-shot timing window.
* +0 Host-admin penalty not applied: host-admin-equivalent privilege is not positively established from the supplied evidence.
* FLOOR 5 applied: yes. First release can end lifetime, exact same reference survives, second operation is a real `hid_put_device()` lifetime/refcount mutation, and the operation is not harmless/idempotent.

3. Reachability analysis

The trigger involves HID-BPF struct_ops registration lifetime and two paths: HID device teardown through `hid_destroy_device()` and BPF registration release through `hid_bpf_unreg()`, for example via BPF map delete when `BPF_F_LINK` is not used.

The vulnerable operation is local. No network path is established.

BPF/HID-BPF setup is privilege-gated in normal Linux deployments. However, the supplied patch does not fully establish whether the complete trigger requires host-root-equivalent privilege, a reduced delegated BPF capability, a service account, or another below-host-admin management context. Therefore `HostAdminRequired=UNKNOWN`.

No complete namespace-scoped trigger is established. The issue is not a netns object and no evidence shows that all required BPF load, HID-BPF attach, device teardown, and unreg stages can be performed inside attacker-created namespaces. Therefore `NamespaceScopedPrivilege=UNKNOWN`.

Prior setup likely includes a HID device and HID-BPF availability. HID devices are common, but HID-BPF struct_ops usage is a specialized control-plane path. No rare physical-only hardware penalty is applied because the vulnerability is in the kernel lifetime handling, not in a rare device quirk.

Race repeatability is plausible for a capable local actor able to attach and release HID-BPF programs while device teardown occurs, but complete attacker control over both sides of the race is not fully established.

4. Primitive and severity interpretation

Exact primitive: a TOCTOU lifetime bug causing double put of the same `struct hid_device` registration reference.

This is an active structured kernel object, not fixed stale storage. The stale object is a `struct hid_device` whose lifetime is managed by references and which remains involved in teardown.

This is not merely an ordinary stale cleanup dereference. The stronger pattern is:

A. ordinary stale cleanup dereference:
stale pointer -> cleanup helper -> fault

versus this case:

B. second lifetime/refcount mutation through a potentially dangling object:
`hid_put_device()` by one path may end lifetime -> same registration reference remains reachable in the racing path -> a second `hid_put_device()` mutates lifetime/refcount state through a potentially freed object.

The patch supports category B.

Primitive class is `CLASS_B`: a real kernel lifetime/refcount corruption primitive exists, but controlled reclaim, arbitrary R/W, callback control, and demonstrated privilege escalation are not established.

Demonstrated consequence: local kernel crash / DoS via UAF during HID device teardown.

Speculative consequence: stronger exploitation may be possible because this is a kernel UAF with a concrete repeated lifetime mutation, but the supplied evidence does not prove a controlled replacement object or LPE chain.

`ImportantCandidate=YES` because a concrete repeated release/refcount UAF leaves meaningful Important-vs-Moderate exploitation leverage unresolved.

`AutoDowngradeAllowed=NO` because automatically closing this as ordinary crash-only would discard a concrete repeated lifetime/refcount mutation through a potentially dangling kernel object.

Likely operational severity: Actionable Moderate at minimum, with manual review needed to decide whether it should be treated as Important in the evaluated product.

5. One-sentence report phrase

A race between HID BPF struct_ops device destroy and unreg can double put the same hid_device registration reference, causing a kernel use after free and at least local denial of service, with unresolved exploitation leverage from the second lifetime mutation.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real UAF with a concrete double put/refcount lifetime mutation on the same object reference, not a simple crash-only NULL dereference or passive cleanup warning.

7. Call-site confidence

Call-site confidence: high

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

Patch: HID: bpf: serialize device reference release in struct_ops destroy path
Commit: 401359684620145be710de97b87e1a47abfe1459
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=401359684620145be710de97b87e1a47abfe1459

Commit description:

__hid_bpf_ops_destroy_device() and hid_bpf_unreg() can race on the
same registration reference, double-putting struct hid_device and
freeing it while hid_destroy_device() still uses it.  Serialize the
remove/NULL decision under hdev->bpf.prog_list_lock so exactly one
path releases each registration reference: unreg re-checks ops->hdev
under the lock and returns without putting when the destroy path
already cleared it; all put_device() calls happen after the lock is
dropped, which is safe because a concurrent unreg then observes
ops->hdev == NULL under the lock.

Background: each successful attach (hid_bpf_ops_reg) acquires one
device reference (hid_get_device()).  Two paths can release it:

- device destruction: hid_destroy_device() -> hid_bpf_destroy_device()
  -> __hid_bpf_ops_destroy_device(), which walks hdev->bpf.prog_list
  under rcu_read_lock() and drops one reference per attached program;
- BPF link release: bpf map delete (no BPF_F_LINK) synchronously calls
  st_ops->unreg() -> hid_bpf_unreg(), which drops the reference for
  its own registration.

The coordination handshake (e->hdev = NULL on the destroy side vs
"if (!hdev) return" on the unreg side) is a TOCTOU check: the two
paths run under different lock domains (rcu_read_lock vs
prog_list_lock), so a concurrent unreg can read ops->hdev as
non-NULL, block on prog_list_lock, and then proceed while the
destroy traversal executes - both paths then drop the same
reference.  The refcount reaches zero legitimately (each decrement
is individually valid), so no refcount_t saturation fires: the
device is simply freed while the transport is still inside
hid_destroy_device(), and subsequent teardown touches freed memory.

The fix serializes the remove/NULL decision under prog_list_lock on
both sides and moves the destroy-side puts outside the lock.  With
the lock held, plain reads/writes of ops->hdev are sufficient; no
READ_ONCE/WRITE_ONCE are added, keeping the patch minimal.

Unlocked-read safety: the unlocked read of ops->hdev at the top of
hid_bpf_unreg() cannot touch a freed device, because the unreg path
itself still holds this registration's reference (released only by
its own hid_put_device() after the lock is dropped), and a destroy
traversal that already cleared ops->hdev makes the lock-internal
re-check return early without any put.  At most one of the two
paths releases each registration reference.

Fixes: ebc0d80 ("HID: bpf: implement HID-BPF through bpf_struct_ops")
Cc: stable@vger.kernel.org
Signed-off-by: Shen Yongchao <grayhat@foxmail.com>
Assisted-by: Hermes:kimi-k3
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hid/bpf/hid_bpf_struct_ops.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=401359684620145be710de97b87e1a47abfe1459

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

The original Linux kernel CVE announcement for CVE-2026-90001 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90001

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: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: unknown
  Paranoid ActionableScore: 5

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).