[CVE-2026-64327][MODERATE REGULAR] usb: gadget: f_fs: Initialize epfile->in early to fix endpoint direction checks

[CVE-2026-64327][MODERATE REGULAR] usb: gadget: f_fs: Initialize epfile->in early to fix endpoint direction checks

[AL-KERNEL]

CVE: CVE-2026-64327
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: gadget: f_fs: Initialize epfile->in early to fix endpoint direction checks
Commit: 82cf1142e5ccf2b6d6d22ef713aaf3e5f2b5716b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82cf1142e5ccf2b6d6d22ef713aaf3e5f2b5716b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64327
Analysis date: Sat, 25 Jul 2026 08:41:35 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / not an Important candidate from the patch alone
Manual review required: YES

Summary:
FunctionFS DMABUF attach can use an incorrect DMA direction before USB host connection because epfile direction is initialized too late, potentially causing stale data exposure, buffer content corruption, or gadget failure for local users with endpoint file access.

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

The original Linux kernel CVE announcement for CVE-2026-64327 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64327

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64327	MODERATE	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:L/UI:N/S:U/C:L/I:L/A:L';CWE-665;CWE-908;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '5.3';DESCR 'FunctionFS DMABUF attach can use the wrong DMA direction because epfile in is not initialized until endpoint enable while userspace ioctls can run earlier. An IN endpoint is then treated as OUT before USB host connection, so DMA mapping and synchronization may be performed with the wrong direction for imported buffers. For the CVSS the PR:L is used for the paranoid score because endpoint file access can be delegated to a local FunctionFS service account after privileged gadget setup. The issue is not network reachable and requires local access to the gadget FunctionFS endpoint files. Impact is mainly incorrect DMA handling with possible stale data exposure, buffer content corruption, or device function failure rather than a proven kernel privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / not an Important candidate from the patch alone (with actual score 3)  SKIP CVE-2026-64327 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	USB SIMPLEFIX DMAorINTERRUPT LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / not an Important candidate from the patch alone**

## 2. Signal breakdown

Paranoid score signals:

* Local delegated trigger: +1
  A local userspace process with access to FunctionFS endpoint files can call early ioctls such as FUNCTIONFS_DMABUF_ATTACH before USB host connection.

* Privileged kernel or device management DMA adjacent path: +1
  The bug affects USB gadget FunctionFS DMABUF handling and DMA direction selection, which is a trusted kernel device and DMA mapping path.

* Confidentiality impact plausible: +1
  Incorrect DMA direction can plausibly cause stale data exposure or incorrect cache synchronization, but no direct info leak primitive is shown.

* Integrity impact plausible: +1
  Wrong DMA direction can plausibly corrupt buffer contents or cause incorrect data transfer semantics.

* Rare or configuration dependent exposure: -1
  The issue requires USB gadget FunctionFS plus the DMABUF import interface and endpoint file access, so it is not a broad default server exposure.

Conservative interpretation:

* Counts DMA adjacent correctness and limited data integrity or availability concern, but does not assume memory corruption, LPE, or broad unprivileged reachability.

## 3. Reachability analysis

The bug is triggered locally from userspace through FunctionFS endpoint files, specifically when a DMABUF related ioctl is issued before endpoint enablement during USB host connection. In typical systems, USB gadget and FunctionFS setup is privileged, but endpoint files may be handed to a reduced privilege gadget service account. Namespaces or containers only matter if the host explicitly exposes the gadget FunctionFS interface or delegates endpoint access. This is not network reachable and is not triggered by ordinary USB packet traffic alone. Realistic exploitation requires a system using USB gadget FunctionFS with DMABUF import support.

Call-site confidence: medium. The patch shows the initialization point and the later endpoint enable point, and the commit identifies FUNCTIONFS_DMABUF_ATTACH as the affected early ioctl path.

## 4. Severity interpretation

This behaves more like an actionable low to borderline Moderate issue than an Important kernel vulnerability. The patch does not show UAF, OOB write, arbitrary write, type confusion, refcount abuse, or a demonstrated privilege escalation primitive. The practical concern is incorrect DMA direction handling, which can cause stale data, buffer content corruption, or gadget malfunction. The theoretical risk is higher than a pure logic cleanup because DMA direction bugs can cross cache coherency and ownership boundaries, but the provided patch does not justify treating it as strong memory corruption.

## 5. One-sentence report phrase

FunctionFS DMABUF attach can use an incorrect DMA direction before USB host connection because epfile direction is initialized too late, potentially causing stale data exposure, buffer content corruption, or gadget failure for local users with endpoint file access.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a DMA direction issue in a device data path, and the real impact depends on how imported DMABUFs are shared, mapped, synchronized, and exposed to the FunctionFS userspace service.

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

Patch: usb: gadget: f_fs: Initialize epfile->in early to fix endpoint direction checks
Commit: 82cf1142e5ccf2b6d6d22ef713aaf3e5f2b5716b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82cf1142e5ccf2b6d6d22ef713aaf3e5f2b5716b

Commit description:

When parsing endpoint descriptors, ffs_data_got_descs() generates the
eps_addrmap which contains the endpoint direction. However, epfile->in
was previously only populated in ffs_func_eps_enable() which executes
upon USB host connection. As a result, early userspace ioctls like
FUNCTIONFS_DMABUF_ATTACH that run before the host connects would see
epfile->in as 0, leading to incorrect DMA directions.

By moving the initialization to ffs_epfiles_create(), epfile->in is
accurate before userspace opens the endpoint files.

Fixes: 7b07a2a ("usb: gadget: functionfs: Add DMABUF import interface")
Cc: stable <stable@kernel.org>
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Neill Kapron <nkapron@google.com>
Link: https://patch.msgid.link/20260619040609.4010746-2-nkapron@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/gadget/function/f_fs.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=82cf1142e5ccf2b6d6d22ef713aaf3e5f2b5716b

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

The original Linux kernel CVE announcement for CVE-2026-64327 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64327

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:L/PR:H/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS score: 5.3

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: 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).