[CVE-2026-64376][LOW] firmware_loader: fix device reference leak in firmware_upload_register()

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

CVE: CVE-2026-64376
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: firmware_loader: fix device reference leak in firmware_upload_register()
Commit: 517676ec7dfca064e08f94007a4abd21969de0a0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=517676ec7dfca064e08f94007a4abd21969de0a0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64376
Analysis date: Sat, 25 Jul 2026 12:37:52 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A privileged firmware upload registration failure path can leak embedded device references by freeing the instance directly instead of using device core reference release, causing only low-risk resource leakage in repeated failure scenarios.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64376 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64376

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64376	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'firmware_upload_register can take the error path after fw_create_instance has initialized the embedded struct device, but the old cleanup path frees the instance directly instead of dropping the device reference. This leaves device core lifetime accounting unbalanced and can leak references or related resources when alloc_lookup_fw_priv fails during firmware upload registration. For the CVSS the PR:H is selected because reliable triggering normally requires administrative control over driver loading, device probing, or firmware upload provider registration rather than access from an ordinary remote user. The issue is not network reachable and has no evident memory corruption primitive. Impact is limited to availability through resource leakage in repeated failure scenarios.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	LEAK ERRORPATH HARDWARE LINUS 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* +1 Real lifetime corruption: the error path violates device core lifetime rules after `device_initialize()` by freeing `fw_sysfs` directly instead of calling `put_device()`.
* +1 Availability impact realistic, paranoid only: repeated privileged triggering could leak device references or related resources over time.

Subtracting signals:

* -2 Requires admin/root or privileged device-management control in typical deployments: reliable triggering normally requires driver or firmware upload provider registration paths, not ordinary user access.
* No remote reachable signal: this is not network-triggerable.
* No generic memory corruption signal: the patch indicates a refcount/resource leak, not UAF, OOB write, double free, type confusion, or attacker-controlled overwrite.
* No LPE signal: no reclaim, callback control, object replacement, or write primitive is shown.

Call-site confidence: high. The relevant allocation, initialization, failure path, and cleanup change are visible in the provided patch.

## 3. Reachability analysis

The bug is reachable only through `firmware_upload_register()` failure handling after `fw_create_instance()` succeeds and `alloc_lookup_fw_priv()` fails. In normal deployments this path is controlled by kernel drivers or privileged device-management code. A local unprivileged user is not expected to be able to trigger it directly. Namespaces or containers do not materially lower the privilege requirement unless a product exposes firmware upload provider registration or device probing to a reduced-privilege service, which would be unusual. The path is not remotely reachable and realistic exploitation is limited to repeated privileged failure-path triggering.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate cleanup/lifetime bug, not an Important-class vulnerability. The theoretical issue is an unbalanced device reference and resource leak. Realistic impact is limited availability degradation from accumulated leaks. There is no demonstrated memory corruption primitive, privilege escalation path, confidentiality impact, or integrity impact.

## 5. One-sentence report phrase

A privileged firmware upload registration failure path can leak embedded device references by freeing the instance directly instead of using device core reference release, causing only low-risk resource leakage in repeated failure scenarios.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a privileged-only refcount/resource leak with no remote reachability, no concrete memory corruption primitive, and no plausible privilege escalation evidence from the patch context.

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UPSTREAM PATCH SUMMARY
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Patch: firmware_loader: fix device reference leak in firmware_upload_register()
Commit: 517676ec7dfca064e08f94007a4abd21969de0a0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=517676ec7dfca064e08f94007a4abd21969de0a0

Commit description:

firmware_upload_register()
  -> fw_create_instance()
     -> device_initialize()

After fw_create_instance() succeeds, the lifetime of the embedded struct
device is expected to be managed through the device core reference
counting, since fw_create_instance() has already called
device_initialize().

In firmware_upload_register(), if alloc_lookup_fw_priv() fails after
fw_create_instance() succeeds, the code reaches free_fw_sysfs and frees
fw_sysfs directly instead of releasing the device reference with
put_device(). This may leave the reference count of the embedded struct
device unbalanced, resulting in a refcount leak.

The issue was identified by a static analysis tool I developed and
confirmed by manual review. Fix this by using put_device(fw_dev) in the
failure path and letting fw_dev_release() handle the final cleanup,
instead of freeing the instance directly from the error path.

Fixes: 97730bb ("firmware_loader: Add firmware-upload support")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Link: https://patch.msgid.link/20260505091231.607089-1-lgs201920130244@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/base/firmware_loader/sysfs_upload.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=517676ec7dfca064e08f94007a4abd21969de0a0

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

The original Linux kernel CVE announcement for CVE-2026-64376 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64376

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: 0
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).