[CVE-2026-46049][LOW] ALSA: ctxfi: Add fallback to default RSR for S/PDIF

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

CVE: CVE-2026-46049
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ALSA: ctxfi: Add fallback to default RSR for S/PDIF
Commit: 25ded535ee261161bcf19dafd525c542e606559d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=25ded535ee261161bcf19dafd525c542e606559d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46049
Analysis date: Wed, 27 May 2026 11:03:27 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local user with access to Creative X-Fi ctxfi S/PDIF passthrough can trigger a 32000 Hz setup path where `pll_rate` remains zero, causing an infinite loop and DoS without memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-46049 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46049

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-2026-46049	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-835;**CWE-400;*CWE-20;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 the ALSA ctxfi S/PDIF passthrough setup path because atc pll_rate may remain 0 after card initialization. When 32000 Hz setup skips atc_pll_init(), the MSR calculation can keep using rsr 0 and spin indefinitely. For the CVSS the PR:L is used because a local user normally needs access to the ALSA device node or an audio service that can configure the ctxfi PCM path. AC:H is used for the realistic score because the issue depends on specific Creative X Fi hardware, S/PDIF passthrough, and the 32000 Hz path. The issue is not network reachable and does not involve UAF, out of bounds access, arbitrary write, information disclosure, or privilege escalation. Impact is denial of service only through an infinite loop or soft lockup.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	SIMPLEFIX HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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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 the ALSA PCM/control device may be able to request the affected S/PDIF passthrough setup.

* Reliable kernel stall / strong DoS: +1
  With `rsr == 0`, the MSR calculation can spin indefinitely and cause a soft lockup.

* Availability impact realistic: +1
  The practical effect is local DoS through a stuck audio driver path or system responsiveness loss.

Subtracting signals:

* Physical/hardware-specific condition: -2
  Requires Creative X-Fi / ctxfi compatible hardware and the S/PDIF passthrough path.

* Special configuration/path condition: -1
  Requires the 32000 Hz case where `atc_pll_init()` is skipped and `pll_rate` remains zero.

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

Score is clamped to Low-like range.

## 3. Reachability analysis

The issue is reachable locally through the ALSA ctxfi S/PDIF passthrough setup path. A remote attacker cannot trigger it directly. The attacker needs access to the relevant ALSA device node or to an audio service capable of configuring this hardware path.

Namespaces and containers matter only if the audio device is delegated to an untrusted workload. Practical exploitation requires affected Creative X-Fi hardware, S/PDIF passthrough usage, and the 32000 Hz path.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate local DoS. The bug is an infinite-loop condition caused by using a zero `pll_rate`, not memory corruption.

Theoretical impact is limited to availability. Realistic evidence does not support confidentiality impact, integrity impact, or privilege escalation.

## 5. One-sentence report phrase

A local user with access to Creative X-Fi ctxfi S/PDIF passthrough can trigger a 32000 Hz setup path where `pll_rate` remains zero, causing an infinite loop and DoS without memory corruption.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a hardware-specific local infinite-loop DoS with no supported memory corruption, remote exposure, or privilege-escalation primitive.

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

Patch: ALSA: ctxfi: Add fallback to default RSR for S/PDIF
Commit: 25ded535ee261161bcf19dafd525c542e606559d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=25ded535ee261161bcf19dafd525c542e606559d

Commit description:

spdif_passthru_playback_get_resources() uses atc->pll_rate as the RSR
for the MSR calculation loop. However, pll_rate is only updated in
atc_pll_init() and not in hw_pll_init(), so it remains 0 after the
card init.

When spdif_passthru_playback_setup() skips atc_pll_init() for
32000 Hz, (rsr * desc.msr) always becomes 0, causing the loop to spin
indefinitely.

Add fallback to use atc->rsr when atc->pll_rate is 0. This reflects
the hardware state, since hw_card_init() already configures the PLL
to the default RSR.

Fixes: 8cc7236 ("ALSA: SB X-Fi driver merge")
Cc: stable@vger.kernel.org
Signed-off-by: Harin Lee <me@harin.net>
Link: https://patch.msgid.link/20260406074913.217374-1-me@harin.net
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/pci/ctxfi/ctatc.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=25ded535ee261161bcf19dafd525c542e606559d

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

The original Linux kernel CVE announcement for CVE-2026-46049 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46049

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).