[CVE-2026-46157][MODERATE REGULAR] ALSA: pcm: oss: Fix data race at accessing runtime.oss.trigger

[CVE-2026-46157][MODERATE REGULAR] ALSA: pcm: oss: Fix data race at accessing runtime.oss.trigger

[AL-KERNEL]

CVE: CVE-2026-46157
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: pcm: oss: Fix data race at accessing runtime.oss.trigger
Commit: 49f9d048845be874df7997e4b1ce662de450c4b6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49f9d048845be874df7997e4b1ce662de450c4b6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46157
Analysis date: Thu, 28 May 2026 11:56:01 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
ALSA PCM OSS accessed `runtime.oss.trigger` without consistent locking, allowing a local race on a bitfield that can corrupt OSS runtime state and potentially cause local denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-46157 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46157

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.

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

CVE-2026-46157	MODERATE	CHECK	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:L/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'ALSA PCM OSS accessed runtime oss trigger without consistent locking, creating a data race on a bitfield. Concurrent reads and writes may also affect adjacent OSS runtime bitfields and leave the PCM OSS state inconsistent, which can cause malfunction or local denial of service. For the CVSS the PR:L is used because a local user needs access to the PCM OSS device interface, but no administrative privileges are required in typical audio device access setups. The issue is not network reachable. Impact is limited to availability and possibly low integrity of kernel audio state, with no supported memory corruption, information disclosure, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-46157  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER RACE HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user with access to ALSA OSS PCM device operations may exercise the affected poll and trigger paths.
* Availability impact realistic: +1. Fuzzing found that the race can confuse OSS PCM state and may cause malfunction or local DoS.
* Broad subsystem exposure: +1. ALSA PCM device access is common on desktop and multimedia systems.

Paranoid additional signal:

* Weak/indirect corruption candidate: +1. The raced field is a bitfield, so writes may disturb adjacent bitfields in the same storage unit and corrupt local OSS runtime state.

Limiting factor:

* Hard/racy condition: -1. The issue depends on concurrent access to the OSS trigger state.
* No generic memory corruption. The patch does not show UAF, OOB write, heap overwrite, arbitrary write, or refcount takeover.
* No information disclosure.
* No privilege escalation primitive.
* No network reachability.

## 3. Reachability analysis

The bug is local and requires access to ALSA OSS PCM interfaces. A user may trigger it by racing OSS PCM operations such as polling and trigger state changes.

Namespaces or containers matter only if audio devices are exposed to untrusted workloads. The issue is not reachable by remote network traffic.

## 4. Severity interpretation

This behaves like a borderline Moderate local DoS or state-corruption issue. The realistic impact is inconsistent PCM OSS state or possible kernel/audio subsystem malfunction.

It does not behave like an Important memory-corruption vulnerability because the corruption is limited to synchronized bitfield state, with no demonstrated arbitrary memory overwrite or LPE path.

## 5. One-sentence report phrase

ALSA PCM OSS accessed `runtime.oss.trigger` without consistent locking, allowing a local race on a bitfield that can corrupt OSS runtime state and potentially cause local denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review whether untrusted users have access to OSS PCM devices. The issue is local and race-dependent, with no proven memory corruption or privilege escalation, but bitfield state corruption justifies manual triage.

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

Patch: ALSA: pcm: oss: Fix data race at accessing runtime.oss.trigger
Commit: 49f9d048845be874df7997e4b1ce662de450c4b6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49f9d048845be874df7997e4b1ce662de450c4b6

Commit description:

Currently the runtime.oss.trigger field may be accessed concurrently
without protection, which may lead to the data race.  And, in this
case, it may lead to more severe problem because it's a bit field; as
writing the data, it may overwrite other bit fields as well, which
confuses the operation completely, as spotted by fuzzing.

Fix it by covering runtime.oss.trigger bit fled also with the existing
params_lock mutex in both snd_pcm_oss_get_trigger() and
snd_pcm_oss_poll().

Reported-and-tested-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Closes: https://lore.kernel.org/20260423145330.210035-1-jjy600901@snu.ac.kr
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260424112205.123703-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/oss/pcm_oss.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=49f9d048845be874df7997e4b1ce662de450c4b6

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

The original Linux kernel CVE announcement for CVE-2026-46157 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46157

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:L/A:H
  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: 3
  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).