[CVE-2026-80970][MODERATE 7.0] ALSA: FCP: do not copy out an uninitialised init response

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

CVE: CVE-2026-80970
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: FCP: do not copy out an uninitialised init response
Commit: 29ab2df278ab4f1d238cd9c1c393ee00db175cba
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29ab2df278ab4f1d238cd9c1c393ee00db175cba
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80970
Analysis date: Fri, 11 Sep 2026 15:54:27 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A local information disclosure in the ALSA FCP ioctl path can copy uninitialized kernel heap bytes, including possible kernel pointers, to userspace when a short USB step0 response is accepted as success.

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

The original Linux kernel CVE announcement for CVE-2026-80970 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80970

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.

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

CVE-2026-80970	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80970 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';*CWE-200;CWE-908;CWE-226;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '5.5';DESCR 'An information disclosure bug in the ALSA FCP ioctl path can copy uninitialized kernel heap bytes to userspace. fcp_ioctl_init allocates the response buffer with kmalloc and later copies the full buffer to the caller, while a short or zero length USB step0 response can leave part of the buffer unchanged. For the CVSS the PR:L is used because a local user or local process must be able to access the ALSA control interface for the affected USB device. The issue is not network reachable. Impact is confidentiality loss only, with possible kernel pointer disclosure and KASLR weakening. The bug requires a suitable or malicious FCP USB device, so real exposure is mostly local systems where such USB audio hardware is attached or can be attached.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	OOB DANGER USB HARDWARE LINUS KPANIC 	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap was applied.

## 2. Signal breakdown

Conservative signals:

* +2: Concrete kernel information disclosure. `fcp_ioctl_init()` allocates a kernel heap buffer with `kmalloc()`, leaves part of it uninitialized after a short USB step0 response, and copies the full buffer to userspace.
* +1: Below-host-admin local reachability. The primitive is exposed through an ALSA ioctl path to a local process with access to the affected device node, not through a host-admin-only kernel-management interface.
* +1: Attacker-influenced disclosure window. The caller controls `step0_resp_size` and `step2_resp_size` in the 1..255 range, influencing the total allocation size and slab-cache class.

Paranoid additional signal:

* +1: Demonstrated sensitive disclosure quality. The supplied evidence shows disclosure of a kernel text pointer and controlled kmalloc-cache pre-seeding behavior, making KASLR weakening and useful heap disclosure plausible.

Material non-awarded signals:

* RealUAF not awarded. No stale lifetime or post-free object use is established.
* Controlled corruption not awarded. The patch shows disclosure from uninitialized memory, not overwrite or object corruption.
* Arbitrary write not demonstrated.
* Integrity impact not awarded.
* Availability impact not awarded.
* Remote reachability not awarded. This is not network-triggerable.
* Strong LPE not awarded. The leak can assist exploitation, but no complete privilege-escalation chain is supplied.
* Hardware rarity penalty not applied. The affected path is device-specific, but the prompt requires concrete evidence before treating hardware specificity as a strong negative.

## 3. Reachability analysis

The evaluated attacker is a local user or local process that can access the ALSA control interface for the affected USB FCP device. Host administrator privilege is not positively required by the supplied call path, so `HostAdminRequired=NO`.

A suitable or malicious USB FCP device is material because the leak depends on the step0 USB control transfer returning a short or zero-length data stage while the kernel accepts it as success. This limits practical exposure to systems where such USB audio hardware is attached or can be attached.

No namespace-scoped privilege is involved. No network trigger is established. No race is required. The behavior is a deterministic ioctl plus short USB response condition rather than a timing-dependent race.

## 4. Primitive and severity interpretation

The exact primitive is a user-visible uninitialized kernel heap disclosure. The kernel allocates `resp` with `kmalloc()`, the device may provide fewer step0 bytes than requested, and the uninitialized remainder is later copied back to userspace.

This is not an active structured-object UAF and not fixed stale storage after free. It is an information disclosure primitive caused by incomplete initialization and insufficient validation of the USB transfer length.

PrimitiveClass is `CLASS_A` because the supplied evidence demonstrates a concrete kernel heap disclosure, including a kernel text pointer. The demonstrated consequence is confidentiality loss. The speculative consequence is that the leak may help bypass KASLR or support another exploit, but no direct LPE or memory corruption chain is established here.

`ImportantCandidate=YES` because concrete kernel heap pointer disclosure should not be automatically downgraded without manual review. `AutoDowngradeAllowed=NO` because the issue exposes real kernel memory to userspace and the supplied evidence shows potentially security-useful leaked data.

Likely operational severity is actionable Moderate, with Important-candidate review justified mainly by kernel pointer disclosure and attacker influence over the allocation size.

## 5. One-sentence report phrase

A local information disclosure in the ALSA FCP ioctl path can copy uninitialized kernel heap bytes, including possible kernel pointers, to userspace when a short USB step0 response is accepted as success.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete kernel heap information leak to userspace with demonstrated kernel pointer disclosure and possible KASLR weakening.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: ALSA: FCP: do not copy out an uninitialised init response
Commit: 29ab2df278ab4f1d238cd9c1c393ee00db175cba
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29ab2df278ab4f1d238cd9c1c393ee00db175cba

Commit description:

fcp_ioctl_init() allocates its response buffer with kmalloc() and copies
the whole buffer back to userspace:

	buf_size = init.step0_resp_size + init.step2_resp_size;

	void *resp __free(kfree) =
		kmalloc(buf_size, GFP_KERNEL);
	...
	if (copy_to_user(arg->resp, resp, buf_size))
		return -EFAULT;

Nothing clears the buffer, and the only writer of its leading
step0_resp_size bytes is the step-0 control transfer:

	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0),
		FCP_USB_REQ_STEP0,
		USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
		0, private->bInterfaceNumber,
		step0_resp, private->step0_resp_size);
	if (err < 0)
		return err;

usb_fill_control_urb() does not set URB_SHORT_NOT_OK, so a short or
zero-length data stage completes with status 0 and snd_usb_ctl_msg()
returns a small actual_length.  The only check is err < 0, so a short
transfer is accepted as success.

snd_usb_ctl_msg() copies the full size back unconditionally:

	buf = kmemdup(data, size, GFP_KERNEL);
	...
	memcpy(data, buf, size);

Bytes the device never wrote are therefore restored into resp unchanged
and copied to userspace.  step0_resp_size and step2_resp_size are each
validated only to 1..255, so the caller also picks the slab cache, from
kmalloc-8 up to kmalloc-512.

On 7.2.0-rc5 (arm64), device answering step 0 with a zero-length data
stage, s0 = s2 = 255:

  # init_on_alloc off, no spray
  step0 window [0,255): nonzero=94/255
  000: 00 80 60 06 00 00 ff ff 18 00 00 00 57 01 ea 01
  010: 08 78 22 13 00 00 ff ff a8 c4 5f 80 00 80 ff ff

  # same kernel, kmalloc-512 pre-seeded with an 8-byte tag
  step0 window [0,255): nonzero=219/255  tagbytes=232

  # identical run, init_on_alloc=1
  step0 window [0,255): nonzero=0/255  tagbytes=0

  # all three runs
  step2 window [255,510): device words matched=62/62

a8 c4 5f 80 00 80 ff ff is the little-endian kernel text address
ffff8000805fc4a8.  The step-2 window is unaffected, so the disclosure is
exactly the step-0 region.

Zero the buffer, and require the step-0 transfer to deliver the full
step0_resp_size bytes so a short data stage is reported as an error.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Fixes: 46757a3 ("ALSA: FCP: Add Focusrite Control Protocol driver")
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260805013804.38839-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/fcp.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=29ab2df278ab4f1d238cd9c1c393ee00db175cba

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

The original Linux kernel CVE announcement for CVE-2026-80970 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80970

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:H/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 4
  Paranoid ActionableScore: 5

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).