[CVE-2026-64134][LOW] ALSA: pcm: Don't setup bogus iov_iter for silencing

[CVE-2026-64134][LOW] ALSA: pcm: Don't setup bogus iov_iter for silencing

[AL-KERNEL]

CVE: CVE-2026-64134
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ALSA: pcm: Don't setup bogus iov_iter for silencing
Commit: 41a766c647294842c9b17672449f8e011048cba9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41a766c647294842c9b17672449f8e011048cba9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64134
Analysis date: Sun, 19 Jul 2026 15:56:24 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local NULL pointer dereference in the ALSA PCM interleaved copy path can occur when PCM silencing reaches the iov_iter transfer path with data NULL, causing a kernel crash on affected RISC-V systems.

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

The original Linux kernel CVE announcement for CVE-2026-64134 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64134

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-2026-64134	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-476;CWE-754;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the ALSA PCM interleaved copy path occurs because the iov_iter based transfer path could be reached with data NULL during silence handling. On affected RISC-V systems this can create a bogus iterator and crash the kernel. For the CVSS the PR:L is used because a local user or process needs access to an ALSA PCM device or an audio service path that can trigger PCM silencing. The issue is not network reachable. Impact is denial of service via kernel crash. No privilege escalation or information disclosure primitive is supported by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	NULLPTR SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	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 user or local process with access to an ALSA PCM device or audio service path may be able to trigger the PCM silencing path.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly states that the bogus iov_iter setup can cause a NULL dereference on RISC-V, which is a plausible kernel crash.

* Rare AND difficult-to-reach subsystem/configuration: -1 in conservative scoring
  The crash is described as architecture-dependent and currently observed on RISC-V, while most architectures did not show trouble. The affected condition also depends on the PCM silencing path.

* No generic memory corruption: +0
  The patch shows NULL data handling before do_transfer. It does not show UAF, double free, OOB write, type confusion, refcount misuse, or attacker-controlled overwrite.

* No privilege escalation plausible: +0
  There is no reclaim primitive, object replacement, write-after-free, callback control, or other LPE-relevant primitive.

* No confidentiality or integrity impact: +0
  The described failure mode is NULL dereference and crash only.

## 3. Reachability analysis

A local user or local service that can open and operate an ALSA PCM device may be able to trigger the affected interleaved PCM silencing path. This is not network reachable. Containers and namespaces generally do not make ALSA devices available unless the device node is deliberately passed through, so container reachability depends on device exposure. The affected subsystem is common on desktop and embedded systems, but the demonstrated crash is architecture-specific to RISC-V and path-specific to silencing with data NULL.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue, not an Important-class vulnerability. The theoretical kernel impact is a NULL dereference crash. The realistic exploitation evidence does not support memory corruption, privilege escalation, information disclosure, or cross-boundary security bypass. The paranoid score keeps the DoS as reliable on affected RISC-V systems but still does not upgrade the bug class.

## 5. One-sentence report phrase

A local NULL pointer dereference in the ALSA PCM interleaved copy path can occur when PCM silencing reaches the iov_iter transfer path with data NULL, causing a kernel crash on affected RISC-V systems.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an auto-close or deferred Moderate unless the affected product exposes ALSA PCM devices to untrusted local users on RISC-V systems where kernel crash availability is considered high priority.

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

Patch: ALSA: pcm: Don't setup bogus iov_iter for silencing
Commit: 41a766c647294842c9b17672449f8e011048cba9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41a766c647294842c9b17672449f8e011048cba9

Commit description:

At transition to the iov_iter for PCM data transfer, we blindly
applied the iov_iter setup also for silencing (i.e. data = NULL), and
it leads to a calculation of bogus iov_iter.  Fortunately this didn't
cause troubles on most of architectures but it goes wrong on RISC-V
now, causing a NULL dereference.

Handle the NULL data case to treat the silencing in interleaved_copy()
for addressing the bug above.  noninterleaved_copy() has already the
NULL data handling, so it doesn't need changes.

Reported-by: Jiakai Xu <xujiakai24@mails.ucas.ac.cn>
Closes: https://lore.kernel.org/20260515051516.3103036-1-xujiakai24@mails.ucas.ac.cn
Fixes: cf393ba ("ALSA: pcm: Add copy ops with iov_iter")
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260517165121.31399-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/pcm_lib.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=41a766c647294842c9b17672449f8e011048cba9

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

The original Linux kernel CVE announcement for CVE-2026-64134 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64134

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:H
  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).