[CVE-2026-46088][LOW] ALSA: control: Validate buf_len before strnlen() in snd_ctl_elem_init_enum_names()

[CVE-2026-46088][LOW] ALSA: control: Validate buf_len before strnlen() in snd_ctl_elem_init_enum_names()

[AL-KERNEL]

CVE: CVE-2026-46088
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ALSA: control: Validate buf_len before strnlen() in snd_ctl_elem_init_enum_names()
Commit: 1fbe46d2b72754d8bd580e13e59ccb5d3d0e8cb0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1fbe46d2b72754d8bd580e13e59ccb5d3d0e8cb0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46088
Analysis date: Wed, 27 May 2026 10:26:03 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local ALSA control input can exhaust the ENUMERATED names buffer and trigger a fortified `strnlen()` BRK panic on affected builds, causing local DoS without memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-46088 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46088

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-46088	LOW	CHECK	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-20;CWE-617;CWE-754;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 local denial of service can occur in snd_ctl_elem_init_enum_names() when the ENUMERATED control names buffer is exhausted but more items remain. The next loop iteration can call strnlen() with buf_len 0, and with CONFIG_FORTIFY_SOURCE a fortified strnlen() check may trigger a BRK exception before the normal EINVAL path is reached. For the CVSS the PR:L is used because a local user needs access to the ALSA control device or an equivalent audio control interface. The issue is not network reachable and does not involve UAF, out of bounds write, arbitrary write, information disclosure, or privilege escalation. Impact is kernel panic DoS only, mainly on affected fortified builds where the compiler loses object size tracking inside the loop.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	DANGER SIMPLEFIX ERRORPATH HARDWARE LINUS TEST  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user with access to ALSA control interfaces can potentially provide crafted ENUMERATED user control names.

* Broad/default/common subsystem exposure: +1
  ALSA control handling is a common local kernel interface on desktop, mobile, and embedded systems with audio enabled.

* Reliable kernel crash / strong DoS: +1
  On affected fortified builds, the fortified `strnlen()` path can trigger a BRK exception and panic the kernel.

* Availability impact realistic: +1
  The practical impact is local kernel panic or system crash.

Subtracting signals:

* Configuration/compiler-dependent condition: -1
  The panic depends on `CONFIG_FORTIFY_SOURCE` behavior and the compiler losing object size tracking in this loop.

* Hard or specific input condition: -1
  The attacker must craft the names buffer so `buf_len` is exhausted while more enum items remain.

No signals apply for memory corruption, UAF, OOB write, arbitrary write, privilege escalation, information disclosure, remote reachability, or security-boundary bypass.

## 3. Reachability analysis

The bug is reachable through local ALSA control creation or update paths for ENUMERATED user-space controls. A normal remote attacker cannot trigger it over the network. Practical reachability depends on whether the local user can access the relevant ALSA control device or an equivalent audio control interface.

Namespaces and containers do not materially increase severity unless audio devices are delegated into the container. The issue is build-dependent because the crash requires fortified `strnlen()` behavior on affected compiler/config combinations.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS. The patch prevents a fortified runtime check from panicking when `strnlen()` is called with `buf_len == 0`.

There is no demonstrated memory corruption primitive. Theoretical impact is kernel panic only, while realistic evidence does not support confidentiality impact, integrity impact, or privilege escalation.

## 5. One-sentence report phrase

A local ALSA control input can exhaust the ENUMERATED names buffer and trigger a fortified `strnlen()` BRK panic on affected builds, causing local DoS without memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a local, build-dependent fortified check panic with DoS-only impact and no supported memory corruption, remote exposure, or privilege-escalation primitive.

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

Patch: ALSA: control: Validate buf_len before strnlen() in snd_ctl_elem_init_enum_names()
Commit: 1fbe46d2b72754d8bd580e13e59ccb5d3d0e8cb0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1fbe46d2b72754d8bd580e13e59ccb5d3d0e8cb0

Commit description:

snd_ctl_elem_init_enum_names() advances pointer p through the names
buffer while decrementing buf_len. If buf_len reaches zero but items
remain, the next iteration calls strnlen(p, 0).

While strnlen(p, 0) returns 0 and would hit the existing name_len == 0
error path, CONFIG_FORTIFY_SOURCE's fortified strnlen() first checks
maxlen against __builtin_dynamic_object_size(). When Clang loses track
of p's object size inside the loop, this triggers a BRK exception panic
before the return value is examined.

Add a buf_len == 0 guard at the loop entry to prevent calling fortified
strnlen() on an exhausted buffer.

Found by kernel fuzz testing through Xiaomi Smartphone.

Fixes: 8d44816 ("ALSA: control: add support for ENUMERATED user space controls")
Cc: stable@vger.kernel.org
Signed-off-by: Ziqing Chen <chenziqing@xiaomi.com>
Link: https://patch.msgid.link/20260414132437.261304-1-chenziqing@xiaomi.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/control.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=1fbe46d2b72754d8bd580e13e59ccb5d3d0e8cb0

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

The original Linux kernel CVE announcement for CVE-2026-46088 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46088

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: unknown
  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).