* [CVE-2026-89979][LOW] ALSA: pcm: Fix race between non-atomic ops and trigger-start
@ 2026-09-16 19:01 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 19:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89979
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ALSA: pcm: Fix race between non-atomic ops and trigger-start
Commit: b1d12144557fceed5de6e22e2c2e30a40ed37702
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1d12144557fceed5de6e22e2c2e30a40ed37702
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89979
Analysis date: Wed, 16 Sep 2026 15:01:44 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89979 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89979
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-2026-89979 LOW https://www.kernelcve.org/list/?q=CVE-2026-89979 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-362;CWE-667;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race in ALSA PCM state handling can allow trigger start to run while non atomic operations such as hw_params, hw_free, or prepare are still active on the same stream. This can create inconsistent PCM runtime state and has been observed by syzkaller as ODEBUG warnings. For the CVSS the PR:L is used because triggering requires a local process with access to the ALSA PCM device rather than full administrative privileges. The issue is not network reachable and is triggered through local sound device operations. Impact is primarily denial of service or subsystem instability. No concrete UAF, OOB write, information disclosure, or privilege escalation primitive is visible from the provided patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES OOB INIT RACE HARDWARE LINUS SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changed the score.
2. Signal breakdown
Positive signals:
* +1 Local below-host-admin trigger: the issue is reachable by a local process that can operate an ALSA PCM device. This is not host-admin-equivalent access.
Negative or non-awarded signals:
* 0 Real UAF not awarded: the patch does not establish use-after-free, stale post-lifetime object use, double release, or refcount mutation.
* 0 Reliable kernel crash not awarded: supplied evidence mentions inconsistent PCM runtime state and ODEBUG warning, not a demonstrated kernel panic or host-wide fatal crash.
* 0 Confidentiality and integrity not awarded: no disclosure, arbitrary write, object corruption, credential impact, or security-boundary bypass is shown.
* 0 Strong or weak LPE concern not awarded: no concrete exploitation primitive beyond inconsistent state is established.
* 0 Structured stale-object leverage not awarded: there is no stale object reuse or post-free field consumption.
* 0 Concrete repeated release/refcount not awarded: no first release, surviving dangling reference, or second lifetime mutation exists.
* 0 Race penalty not applied: although this is a race, the attacker can likely run concurrent operations on the same PCM stream. The evidence does not show a narrow one-shot or externally uncontrollable timing window.
* 0 Remote reachability not awarded: the trigger is local ALSA PCM operations, not network traffic.
3. Reachability analysis
The likely trigger is a local process issuing concurrent ALSA PCM operations on the same stream, for example one thread performing PREPARE or HW_PARAMS while another thread issues trigger start. The relevant access is to the local sound device, typically through `/dev/snd/*` permissions or an equivalent audio service path. This is below host-admin in normal desktop or audio-user scenarios, so HostAdminRequired=NO.
No network trigger is established. No namespace-scoped capability is involved. No prior host-admin setup is required beyond the system having ALSA PCM devices available and accessible to the local user or service. No special rare hardware requirement is established beyond ordinary ALSA PCM device availability. The race is local and repeatable by coordinating operations on the same stream, so no hard timing penalty is applied.
4. Primitive and severity interpretation
The primitive is a PCM state-transition race between non-atomic operations such as `hw_params`, `hw_free`, or `prepare` and the atomic trigger-start path. The vulnerable path allowed `snd_pcm_pre_start()` to proceed while `runtime->buffer_accessing` indicated that a non-atomic buffer operation was in progress.
This is not an active structured UAF and not fixed stale storage. It is an invalid-state or synchronization bug. The demonstrated consequence is subsystem inconsistency and ODEBUG warning. A stronger kernel crash, memory corruption, information leak, or privilege escalation path is not supported by the supplied patch context.
PrimitiveClass=CLASS_C because the established behavior is invalid state / warning / possible local DoS-like instability without an independently useful corruption primitive. ImportantCandidate=NO because there is no Class A primitive and no Class B lifetime/corruption primitive requiring Important-vs-Moderate review. AutoDowngradeAllowed=YES because no unresolved memory-corruption, ownership, authorization, or boundary-bypass primitive remains.
Likely operational severity is low-end Moderate or Low-like local DoS / subsystem instability.
5. One-sentence report phrase
A local ALSA PCM race can allow trigger start to run during hw_params, hw_free, or prepare on the same stream, causing inconsistent runtime state and ODEBUG warnings without a demonstrated memory corruption or privilege escalation primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The issue appears to be a local synchronization bug with warning or minor DoS-style impact only, and the supplied evidence does not establish UAF, OOB access, repeated lifetime mutation, information disclosure, authorization bypass, or privilege escalation.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: pcm: Fix race between non-atomic ops and trigger-start
Commit: b1d12144557fceed5de6e22e2c2e30a40ed37702
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1d12144557fceed5de6e22e2c2e30a40ed37702
Commit description:
We protect the races of the concurrent state transitions between
atomic PCM ops, but the checks between the non-atomic ops (hw_params,
hw_free and prepare) and the atomic ops aren't perfect; there is a
check of the conflicting PCM state at the beginning of hw_params & co,
but the atomic PCM ops can be still issued during the non-atomic PCM
operations. An example such scenario is that a thread A re-issues the
PREPARE or HW_PARAMS for the already prepared stream, while another
thread B triggers the PCM start in the middle of the prepare
operation. Although this usually doesn't lead to much serious issues,
it can give some inconsistency as reported by syzkaller (such as
ODEBUG warning).
There are various atomic PCM ops, and basically the only problem is
the PCM start as it operates from the PREPARED state. Other trigger
commands (stop, etc) are for the running or the other special state,
hence they are filtered as pre-condition.
This patch is for preventing the PCM trigger-start during the non-
atomic operations in order to address the problems above.
Fortunately, the hw_params, hw_free and prepare operations call
snd_pcm_buffer_access_lock(), and this can be used for checking the
concurrent operations at the PCM trigger -- which sets the
runtime->buffer_accessing to a negative (if possible), so the PCM
trigger just needs to check the runtime->buffer_accessing value; if
it's negative, it means the concurrent non-atomic PCM ops is running.
Reported-by: [email protected]
Closes: https://lore.kernel.org/[email protected]
Cc: <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
sound/core/pcm_native.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=b1d12144557fceed5de6e22e2c2e30a40ed37702
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89979 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89979
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: unknown
Paranoid ActionableScore: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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