[CVE-2026-80716][MODERATE 7.0] ALSA: pcm: wake linked drain waiters on unlink

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

CVE: CVE-2026-80716
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: pcm: wake linked drain waiters on unlink
Commit: c172e4c53321ee6429955295ea133bc3597a3ca9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c172e4c53321ee6429955295ea133bc3597a3ca9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80716
Analysis date: Fri, 28 Aug 2026 05:47:38 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free in ALSA PCM linked stream handling can leave an on-stack drain wait entry queued after snd_pcm_unlink(), allowing a later wake_up to walk a freed stack frame and potentially cause a kernel crash or, in the worst case, privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80716 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80716

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 7.0
Manual review required: YES

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-2026-80716	MODERATE	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free in ALSA PCM linked stream handling can occur when snd_pcm_drain() leaves an on stack wait entry queued on a peer runtime sleep list after group membership changes during snd_pcm_unlink(). A later wake_up can walk the stale wait entry after the draining function has returned, which means the kernel may dereference data from a freed stack frame. For the CVSS the PR:L is used because a local user with access to ALSA PCM devices can potentially exercise linked streams and trigger drain and unlink operations without full administrator privileges. AC:H is used because reliable triggering depends on a race window involving drain wait, unlink, and signal or timeout behavior. The issue is not network reachable and requires local interaction with the sound subsystem. Impact is at least local denial of service via kernel crash. In the paranoid assessment, the stack based UAF makes privilege escalation plausible enough for manual review even if the most direct symptom is a crash.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	LOCK UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user with access to ALSA PCM devices may exercise linked PCM streams, drain, unlink, signal, and timeout behavior without full host root.
* Memory corruption, Strong corruption primitive: +2. The bug leaves an on-stack wait entry queued after the function returns, and later wake_up walks a stale stack object.
* Real lifetime corruption: +1. This is a real lifetime bug involving a wait_queue_entry that outlives its stack frame.
* Reliable kernel crash / strong DoS: +1. A later wake_up can dereference the stale wait entry and crash the kernel.
* Hard or unreliable race / special timing required: -1. Reliable triggering depends on a race window involving snd_pcm_drain(), snd_pcm_unlink(), and signal or timeout completion.
* Weak LPE concern: +1. The stale object is a wait queue entry and wake_up may reach callback related fields, but the patch does not demonstrate controlled reclaim or a complete exploitation primitive.

Paranoid adjustment:

* Strong LPE plausibility: elevated from weak concern because stale on-stack wait queue entries are walked by wake_up and wait queue entries include callback semantics.
* Confidentiality impact plausible and Integrity impact plausible are considered for paranoid triage only, because successful control of the stale stack object could theoretically move beyond DoS.
* Paranoid score is kept at 7 rather than higher to avoid over-counting the same UAF primitive multiple times.

## 3. Reachability analysis

The bug is local and not network reachable. The likely attacker is a local user or process with access to ALSA PCM device nodes. On desktop systems this may include users in the audio group or users accessing audio through a local session stack. On locked-down servers or containers without sound devices exposed, reachability is much lower.

Namespaces do not inherently make the ALSA device available. Container impact depends on whether the host exposes sound device nodes into the container and whether device cgroup or LSM policy permits access. This is not a CAP_SYS_ADMIN-only path in typical desktop-like configurations, so PR:L is the practical CVSS interpretation.

Call-site confidence: high. The commit message directly describes snd_pcm_drain(), snd_pcm_unlink(), the on-stack wait entry, runtime sleep list, and later wake_up traversal.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is a concrete UAF/lifetime bug, not just a warning or resource leak. The realistic demonstrated impact is local kernel crash DoS. The theoretical higher impact is privilege escalation through stale stack wait queue object reuse, but the patch does not prove a controlled reclaim or full exploit chain.

Therefore, the conservative score is Actionable Moderate, while the paranoid score makes it a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A local use-after-free in ALSA PCM linked stream handling can leave an on-stack drain wait entry queued after snd_pcm_unlink(), allowing a later wake_up to walk a freed stack frame and potentially cause a kernel crash or, in the worst case, privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

This should not be auto-closed because it is a real UAF on a stack wait queue entry with later wake_up traversal, local unprivileged reachability in common audio configurations, and plausible but unproven LPE potential.

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

Patch: ALSA: pcm: wake linked drain waiters on unlink
Commit: c172e4c53321ee6429955295ea133bc3597a3ca9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c172e4c53321ee6429955295ea133bc3597a3ca9

Commit description:

snd_pcm_drain() on a linked stream parks an on-stack wait entry on the
drained peer's runtime->sleep, and after schedule_timeout() removes it
only if that peer is still found in the caller's group.  If group
membership changes during the wait and the sleep ends by signal or
timeout (so autoremove_wake_function() does not run), finish_wait() is
skipped and snd_pcm_drain() returns with the entry still queued on that
stream's sleep list; a later wake_up() then walks a freed stack frame.
This is reachable by unlinking either the drained or the draining stream.

Unlike the close path (snd_pcm_drop() -> snd_pcm_post_stop()),
snd_pcm_unlink() never wakes the sleep queues.  Wake every group member
under the group lock before the membership change, so a linked drainer is
released and drops its entry while the streams are still grouped.

The window was opened when snd_pcm_link_rwsem stopped being held across
the wait and the removal became conditional on group membership (see
Fixes). The later switch to finish_wait() kept that conditional removal,
so the signal/timeout case remained.

Fixes: f57f3df ("ALSA: pcm: More fine-grained PCM link locking")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Link: https://patch.msgid.link/A0705100-D10B-4286-9980-0142ABEEAD51@doyensec.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=c172e4c53321ee6429955295ea133bc3597a3ca9

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

The original Linux kernel CVE announcement for CVE-2026-80716 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80716

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:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 5
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).