[CVE-2026-68217][LOW] media: pwc: Drain fill_buf on start_streaming() failure

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

CVE: CVE-2026-68217
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: media: pwc: Drain fill_buf on start_streaming() failure
Commit: a56e7641e09bd80b976e944ae759109b86fd5b38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a56e7641e09bd80b976e944ae759109b86fd5b38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68217
Analysis date: Mon, 10 Aug 2026 12:49:05 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local user with access to the PWC V4L2 camera device may trigger a start_streaming failure race that leaves a vb2 buffer owned by the driver, causing a WARN and local denial of service, with kernel panic possible only on panic_on_warn systems.

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

The original Linux kernel CVE announcement for CVE-2026-68217 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68217

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
======================================================================

CVE-2026-68217	LOW	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:N/I:N/A:H';*CWE-772;CWE-459;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The pwc V4L2 USB camera driver can leave a vb2 buffer owned by the driver when start_streaming fails after an isochronous URB completion already moved a queued buffer into pdev fill_buf. This creates a buffer ownership leak and can trigger WARN_ON owned_by_drv_count in vb2_start_streaming, causing a local denial of service for the video device and possibly a kernel level DoS if warnings are configured to panic. For the CVSS the PR:L reflects that a local process needs access to the V4L2 video device and must attempt streaming while USB URB setup fails. The issue is not network reachable. No UAF or arbitrary write primitive is indicated by the code change, so confidentiality and integrity impact are not assigned.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	USB WARNONLY LEAK ERRORPATH HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process with access to the V4L2 video device can attempt streaming.
* Availability impact realistic: +1
  The bug can leave a vb2 buffer owned by the driver and trigger `WARN_ON(owned_by_drv_count)`, causing local device DoS or failed streaming state.
* Hard or unreliable race / special timing required: -1
  Trigger requires an URB completion to move a buffer into `pdev->fill_buf` before a later URB submission fails.
* No memory corruption bonus: +0
  The patch shows a buffer ownership leak, not UAF, double free, OOB write, type confusion, or arbitrary write.
* No LPE signal: +0
  There is no attacker-controlled reclaim, callback corruption, stale freed object reuse, or write primitive.

Paranoid additional signal:

* Reliable kernel crash / strong DoS: +1
  Only in hardened deployments where `panic_on_warn` is enabled, the WARN can become a system-wide kernel DoS.

Call-site confidence: high. The commit message provides the relevant start_streaming, URB completion, cleanup, and vb2 ownership path.

## 3. Reachability analysis

The bug is locally reachable through a PWC V4L2 USB camera device. A normal user may be able to trigger it if they have permission to open the corresponding `/dev/video*` node, commonly through the `video` group or device ACLs.

It is not network reachable. Containers or namespaces do not materially improve reachability unless the video device is explicitly passed through to the container.

The affected path is hardware and driver specific. It requires a PWC USB camera and an error during URB submission after at least one URB completion has already run, so practical triggering is conditional and timing dependent.

## 4. Severity interpretation

This behaves like a low-end Moderate or Low-like local DoS, not an Important-class vulnerability. The realistic impact is a V4L2 buffer ownership leak that can trigger a WARN and leave streaming cleanup inconsistent.

Theoretical kernel-wide DoS is possible only if WARNs are configured to panic. There is no evidence in the patch of UAF, double free, arbitrary write, object replacement, callback control, or privilege escalation.

## 5. One-sentence report phrase

A local user with access to the PWC V4L2 camera device may trigger a start_streaming failure race that leaves a vb2 buffer owned by the driver, causing a WARN and local denial of service, with kernel panic possible only on panic_on_warn systems.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed or deprioritized for most security triage workflows because it is local, device-specific, timing/error-path dependent, and does not show a concrete memory corruption or privilege escalation primitive.

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

Patch: media: pwc: Drain fill_buf on start_streaming() failure
Commit: a56e7641e09bd80b976e944ae759109b86fd5b38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a56e7641e09bd80b976e944ae759109b86fd5b38

Commit description:

pwc_isoc_init() submits its isochronous URBs with
usb_submit_urb(.., GFP_KERNEL) in a loop. After the first URB is
submitted, its completion handler pwc_isoc_handler() can run on another
CPU before the loop finishes:

  start_streaming()
    pwc_isoc_init()
      usb_submit_urb(urbs[0], GFP_KERNEL)
                                  pwc_isoc_handler(urbs[0])
                                    pdev->fill_buf =
                                      pwc_get_next_fill_buf(pdev)
      usb_submit_urb(urbs[i>0], ..)  -> fails
      pwc_isoc_cleanup(pdev)           /* kills URBs */
      return ret;
    pwc_cleanup_queued_bufs(pdev, VB2_BUF_STATE_QUEUED)

pwc_get_next_fill_buf() detaches a buffer from pdev->queued_bufs and
stores it in pdev->fill_buf. The error path in start_streaming() only
drains pdev->queued_bufs, so the buffer parked in pdev->fill_buf is
leaked. vb2_start_streaming() then triggers
WARN_ON(owned_by_drv_count).

stop_streaming() already handles this since commit 80b0963
("[media] pwc: fix WARN_ON"), which added the fill_buf drain in the
teardown path but not in the start_streaming() error path. Mirror that
handling on failure so start_streaming() returns with no buffer owned
by the driver.

Issue identified by automated review of the INV-003 series at
https://sashiko.dev/

Fixes: 885fe18 ("[media] pwc: Replace private buffer management code with videobuf2")
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=a56e7641e09bd80b976e944ae759109b86fd5b38

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

The original Linux kernel CVE announcement for CVE-2026-68217 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68217

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).