[CVE-2026-80951][IMPORTANT] i3c: master: svc: bound IBI payload to the requested max_payload_len

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

CVE: CVE-2026-80951
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: i3c: master: svc: bound IBI payload to the requested max_payload_len
Commit: f296a0d5907bf88314dfda67245f7f69d1552470
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f296a0d5907bf88314dfda67245f7f69d1552470
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80951
Analysis date: Fri, 11 Sep 2026 16:31:36 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80951 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80951

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: IMPORTANT
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-2026-80951	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-80951 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-119;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'An out of bounds write in the Silvaco I3C master IBI receive path can occur because svc_i3c_master_handle_ibi() bounded reads by the hardware FIFO size instead of the per slot max_payload_len requested by the client driver. A malicious or compromised I3C device can send an IBI payload larger than the allocated slot size, causing readsb() to write past slot data into the IBI pool. For the CVSS the PR:N is used because the attacker does not need local code execution or privileges on the host once a hostile device can signal on the I3C bus. The issue is not Internet network reachable and is best modeled as adjacent bus access rather than AV:N. Impact is at least denial of service via kernel memory corruption, with plausible confidentiality and integrity impact in the paranoid score because the primitive is an OOB write in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6)	YES	WRITE OOB INIT SIMPLEFIX LEAK HARDWARE LINUS 	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 7
* Applied paranoid floor/cap: Class A important-preservation floor 6 -> 7 for a concrete attacker-influenced kernel OOB write reachable from a hostile device without host-admin privilege.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive. The patch establishes an attacker-influenced out-of-bounds write: readsb() copies RX FIFO bytes past slot->data when max_payload_len is smaller than SVC_I3C_FIFO_SIZE.
* +1 Firmware-mediated external influence. The trigger comes from a malicious or compromised I3C device sending an oversized IBI payload, not from ordinary local code or direct Internet traffic.
* +1 Reliable kernel crash / strong DoS. The write corrupts kernel memory in the IBI pool and can realistically cause kernel malfunction or crash.
* +1 Weak exploitation concern for conservative scoring. The attacker controls the device-supplied payload bytes and can exceed a small requested slot size such as max_payload_len 1, although the overwritten target is constrained to adjacent IBI pool memory.
* +1 Integrity plausible for paranoid scoring. The primitive is a controlled write beyond an allocated kernel buffer into another kernel-owned region, but exact sensitive target control is not demonstrated.

Non-awarded / limiting signals:

* RealUAF not awarded. This is an OOB write, not a lifetime or stale-reference bug.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality not awarded. No read-back or disclosure path is shown.
* Direct remote network reachability not established. This is adjacent/device-bus reachable, not AV:N style packet reachability.
* Extra Availability not awarded. The same crash/corruption consequence is already counted once.
* Physical-only / rare hardware penalty not applied as a hard negative because the supplied evidence establishes a concrete hostile-device trigger path. Exposure is still deployment-limited to systems using this Silvaco I3C master path and IBI-capable devices.

3. Reachability analysis

The relevant attacker is a malicious or compromised I3C device capable of sending an IBI payload larger than the host driver requested. The attacker does not need host local code execution or host administrative privileges once such a device can signal on the I3C bus.

This is not namespace-scoped. Linux user namespaces or network namespaces do not materially affect this trigger path.

The complete trigger requires an affected system with the Silvaco I3C master driver and an IBI client configuration where max_payload_len can be smaller than the hardware FIFO size. The commit gives mctp-i3c requesting 1 byte as a concrete example. Prior platform configuration and attached device topology matter for exposure, but they do not make the attacker host-admin in the device-threat model.

Race repeatability is not a key constraint. The bug is a deterministic bounds error in the IBI receive path when oversized device data is present.

4. Primitive and severity interpretation

The exact primitive is an attacker-influenced kernel heap/buffer out-of-bounds write from the I3C RX FIFO into the IBI pool. The vulnerable loop was bounded by SVC_I3C_FIFO_SIZE instead of dev->ibi->max_payload_len, and the per-read count was not clamped to remaining slot capacity.

This is not fixed stale storage and not a cleanup/destructor UAF. It is direct memory corruption of kernel-managed IBI pool storage. The target is constrained because the write goes past the current slot into nearby pool memory rather than to an arbitrary address, but the primitive is still stronger than crash-only invalid dereference because attacker-supplied device bytes are copied out of bounds.

PrimitiveClass is CLASS_A because a concrete attacker-influenced OOB write into kernel memory is established. Demonstrated consequence is at least kernel memory corruption and DoS. Speculative consequence is stronger corruption impact depending on adjacent object layout in the IBI pool, but arbitrary R/W or privilege escalation is not proven.

ImportantCandidate=YES because concrete kernel memory corruption with attacker-controlled input should not be automatically downgraded. AutoDowngradeAllowed=NO because the established OOB write is a meaningful unresolved corruption primitive, even though exposure is adjacent/device-bus rather than Internet remote.

Likely operational severity: strong Important candidate for affected hardware deployments, especially where I3C devices are externally attachable, replaceable, or firmware-compromisable.

5. One-sentence report phrase

A malicious or compromised I3C device can send an oversized IBI payload that makes the Silvaco I3C master driver copy beyond the allocated IBI slot into the kernel IBI pool, causing kernel memory corruption and likely DoS with unresolved stronger exploitation potential.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete attacker-influenced kernel OOB write into an active kernel pool is established, while exact object adjacency and exploitation leverage require manual kernel memory-layout review.

7. Call-site confidence

Call-site confidence: high

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

Patch: i3c: master: svc: bound IBI payload to the requested max_payload_len
Commit: f296a0d5907bf88314dfda67245f7f69d1552470
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f296a0d5907bf88314dfda67245f7f69d1552470

Commit description:

svc_i3c_master_handle_ibi() reads the IBI payload from the RX FIFO into
the IBI slot. The loop is bounded by the hardware FIFO size
(SVC_I3C_FIFO_SIZE), not by the slot size.

slot->data points into the IBI pool, which i3c_generic_ibi_alloc_pool()
sizes at max_payload_len per slot. svc_i3c_master_request_ibi() only
rejects a max_payload_len larger than SVC_I3C_FIFO_SIZE, so a driver can
request a smaller one. mctp-i3c requests 1. Each readsb() then copies the
controller RXCOUNT bytes (up to 31) with no check against the slot size.
A device that sends more bytes than the slot holds writes past
slot->data, an out-of-bounds write into the IBI pool.

Bound the loop by dev->ibi->max_payload_len and clamp each read to the
space left in the slot, the same way dw-i3c does. A device can still send
more than the requested payload. Flush the leftover bytes from the RX FIFO
so they do not leak into the next transfer.

Fixes: dd3c528 ("i3c: master: svc: Add Silvaco I3C master driver")
Cc: stable@vger.kernel.org
Co-developed-by: Kaixuan Li <kaixuan.li@ntu.edu.sg>
Signed-off-by: Kaixuan Li <kaixuan.li@ntu.edu.sg>
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/178227747353.2931373.15868718612134648277@maoyixie.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/i3c/master/svc-i3c-master.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=f296a0d5907bf88314dfda67245f7f69d1552470

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

The original Linux kernel CVE announcement for CVE-2026-80951 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80951

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT

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).