[CVE-2026-68216][LOW] media: pwc: Return queued buffers on start_streaming() failure

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

CVE: CVE-2026-68216
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: media: pwc: Return queued buffers on start_streaming() failure
Commit: f2f9fcacd81953dde6cb86312ab13ca13e689664
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f2f9fcacd81953dde6cb86312ab13ca13e689664
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68216
Analysis date: Mon, 10 Aug 2026 13:23:57 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
The pwc V4L2 driver failed to return already queued vb2 buffers when start_streaming() exited early, allowing a local process with video-device access to trigger WARN conditions and buffer leaks that may cause device-level denial of service.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68216 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68216

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-2026-68216	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:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-755;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The pwc V4L2 driver could fail start_streaming after vb2 had already queued buffers to the driver. In the USB disconnect path and in the interruptible mutex failure path, those queued buffers were not returned to vb2, which can trigger a WARN and leave buffers owned by the driver. For the CVSS the PR:L is used because a local user or process generally needs access to the affected video device to start streaming and trigger the failing path. The issue is not network reachable and requires local device interaction or a local process using the camera interface. Impact is denial of service through leaked video buffers, failed streaming, warning noise, and possible resource exhaustion after repeated failures.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	LOCK USB WARNONLY SIMPLEFIX LEAK ERRORPATH DMAorINTERRUPT HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process with access to the affected V4L2 video device can call streaming operations and hit the failing paths.
* Availability impact realistic: +1 in the paranoid score. Queued buffers can remain owned by the driver, streaming can fail, and repeated failures may cause resource leakage or device-level DoS.
* WARN_ON continuation rule: +0. The patch describes WARN_ON(owned_by_drv_count), but no concrete panic, UAF, OOB access, double free, or privilege escalation primitive.
* Resource leak only: no memory-corruption bonus. The bug is missing cleanup of vb2 buffers on error paths, not attacker-controlled memory corruption.
* Rare device-specific exposure: -1. The issue is specific to the pwc USB camera driver and requires the affected hardware or device node.

## 3. Reachability analysis

The bug is locally reachable through the V4L2 camera interface if a user or process has permission to access the pwc video device. It is not network reachable. Containers or namespaces matter only if the video device is passed through into the container. The USB disconnect path may require physical or device-management conditions, while the interrupted mutex path can be hit by local process behavior. The affected driver is hardware-specific and not a broad default kernel attack surface.

Call-site confidence: high. The patch directly shows the failing start_streaming() early returns and the missing cleanup calls.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource cleanup bug. The realistic impact is denial of service for the camera streaming path or possible resource leakage after repeated failures. There is no evidence of UAF, OOB access, stale callback, object replacement, arbitrary write, information disclosure, or privilege escalation.

## 5. One-sentence report phrase

The pwc V4L2 driver failed to return already queued vb2 buffers when start_streaming() exited early, allowing a local process with video-device access to trigger WARN conditions and buffer leaks that may cause device-level denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a constrained resource-leak and error-path cleanup issue with no demonstrated memory corruption or security-boundary bypass.

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UPSTREAM PATCH SUMMARY
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Patch: media: pwc: Return queued buffers on start_streaming() failure
Commit: f2f9fcacd81953dde6cb86312ab13ca13e689664
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f2f9fcacd81953dde6cb86312ab13ca13e689664

Commit description:

The vb2 framework hands buffers to the driver via buf_queue() before
calling start_streaming().  If start_streaming() returns an error
without first returning those buffers via vb2_buffer_done(),
vb2_start_streaming() fires WARN_ON(owned_by_drv_count) and the queued
buffers leak.

pwc's start_streaming() had two early returns that hit this trap:
-ENODEV when the USB device was already disconnected, and -ERESTARTSYS
when mutex_lock_interruptible() was interrupted by a signal.  Call the
existing pwc_cleanup_queued_bufs() helper with VB2_BUF_STATE_QUEUED
before returning (matching the state already used by the
pwc_isoc_init() error path in the same function).

This mirrors the uvcvideo fix in commit 4cf3b6f ("media: uvcvideo:
Return queued buffers on start_streaming() failure").

Fixes: ceede9f ("[media] pwc: Fix locking")
Cc: stable@vger.kernel.org
Signed-off-by: Valery Borovsky <vebohr@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/usb/pwc/pwc-if.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=f2f9fcacd81953dde6cb86312ab13ca13e689664

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

The original Linux kernel CVE announcement for CVE-2026-68216 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68216

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1
  Paranoid ActionableScore: 2

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).