[CVE-2026-98204][MODERATE REGULAR] Input: rmi_smbus - fix out-of-bounds read in rmi_smb_write_block()

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

CVE: CVE-2026-98204
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Input: rmi_smbus - fix out-of-bounds read in rmi_smb_write_block()
Commit: d01337c0892d1509500c727edf81380777c2dd0f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d01337c0892d1509500c727edf81380777c2dd0f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98204
Analysis date: Fri, 09 Oct 2026 04:23:43 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98204 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98204

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 REGULAR
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
======================================================================

CVE-2026-98204	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98204 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L';CWE-125;CWE-126;CWE-193;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.5';DESCR 'An out of bounds read occurs in rmi_smb_write_block because every SMBus chunk is calculated from the original transfer length instead of the remaining length. For a transfer larger than 32 bytes with a partial final chunk, smb_block_write can read up to 31 bytes beyond the end of the input buffer and transmit those bytes to the attached RMI SMBus device. The demonstrated primitive is a bounded invalid read with possible limited disclosure of adjacent kernel data. No out of bounds write or other direct memory corruption primitive is present. For the CVSS the PR:N applies to the physical attack interpretation because an attacker with access to the device or SMBus does not require a local account, although practical exploitation depends on the affected RMI hardware and the ability to reach a transfer with a suitable length. The issue is not remotely network reachable. Impact is primarily limited confidentiality loss. A kernel fault is a conservative worst case if the over read reaches inaccessible memory, but reliable privilege escalation is not supported by this code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	WRITE OOB SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1.
* Conservative score: 0.
* Raw paranoid score: -1.
* Paranoid score: 0.
* Applied score lower bound: -1 -> 0.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Confidentiality plausible. The final SMBus transaction may copy up to 31 bytes beyond the source buffer and transmit them to the attached RMI device, providing a concrete but limited device-visible disclosure path.
* -2 Physical-only exploitation context. Observing the excess bytes requires control of or physical visibility into the affected RMI SMBus device or bus. No local userspace or network disclosure path is established.
* +0 Weak corruption concern. The primitive is a bounded OOB read, not an OOB write.
* +0 Availability. A fault is theoretically possible if the read crosses inaccessible memory, but a realistic or reliable kernel crash is not established.
* +0 B5-R. The supplied B5-R profile does not apply because condition 1 fails. There is no heap OOB write. Conditions 2 through 4 also fail because there is no retry-accumulated offset, attacker-influenced retry sequence, or later consumption of corrupted structured state.
* Controlled reclaim, arbitrary write, UAF, active-state corruption, privilege escalation, and remote reachability are not demonstrated.
* No C or I impact beyond the limited device-visible read is inferred.

3. Reachability analysis

The vulnerable function is used by the Synaptics RMI4 SMBus transport. A transfer longer than 32 bytes with a non-aligned final chunk reaches the over-read, but the supplied patch does not show which callers permit an attacker to select such a length.

The complete trigger is therefore unresolved with respect to an ordinary local user, a privileged device-management process, or normal driver activity. Host-admin privilege is not proven, but below-host-admin invocation is also not established, so HostAdminRequired is UNKNOWN.

No namespace capability is involved. No network trigger exists. Practical extraction of the excess bytes requires an attached malicious device, SMBus observation, or equivalent physical access. This is deterministic length-accounting behavior, not a race or retry condition.

4. Primitive and severity interpretation

The exact primitive is a bounded read of up to 31 bytes beyond the end of `databuff`, followed by transmission through `smb_block_write`. It is not a write outside kernel memory and does not corrupt a descriptor, pointer, operation array, refcount, or active structured object.

There is no stale storage, lifetime violation, repeated release, or UAF. PrimitiveClass is CLASS_C because the issue is a constrained invalid read with a limited disclosure sink and no established stronger corruption primitive.

The demonstrated consequence is possible disclosure of adjacent kernel bytes to the attached SMBus device. A kernel fault is a theoretical boundary case rather than a demonstrated reliable consequence. ImportantCandidate is NO because no Important-preserving primitive or practical low-privilege disclosure chain is established. AutoDowngradeAllowed is YES because the issue remains a physically constrained, bounded OOB read without unresolved write or lifetime leverage.

5. One-sentence report phrase

A final partial RMI SMBus write can read and transmit up to 31 bytes beyond its kernel input buffer, but exploitation appears physically constrained and no memory write, UAF, network trigger, or privilege escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review callers and source-buffer allocation boundaries to determine whether an attacker can select the transfer length and whether the attached device can expose sensitive adjacent bytes.

7. Call-site confidence

Call-site confidence: medium

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

Patch: Input: rmi_smbus - fix out-of-bounds read in rmi_smb_write_block()
Commit: d01337c0892d1509500c727edf81380777c2dd0f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d01337c0892d1509500c727edf81380777c2dd0f

Commit description:

When chunking writes into SMBus blocks in rmi_smb_write_block(), the
loop calculates block_len using the original total length (len) instead
of the remaining length (cur_len).

If len is greater than 32 bytes (SMB_MAX_COUNT), block_len remains 32
for every iteration, even on the final partial chunk where fewer than 32
bytes remain. This causes smb_block_write() to read 32 bytes from the
advanced data buffer pointer, reading past the end of the input buffer.

Fix this by calculating block_len using cur_len and advancing the buffer
and address pointers by block_len.

Fixes: 82264d0 ("Input: synaptics-rmi4 - add SMBus support")
Cc: stable@vger.kernel.org
Reported-by: sashiko-bot@kernel.org
Assisted-by: LLM
Link: https://patch.msgid.link/anLFSMKSoKyyZ272@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/input/rmi4/rmi_smbus.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=d01337c0892d1509500c727edf81380777c2dd0f

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

The original Linux kernel CVE announcement for CVE-2026-98204 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98204

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS score: 3.5

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: 0

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).