[CVE-2026-98848][LOW] rtc: ac100: Assign .num before accessing .hws

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

CVE: CVE-2026-98848
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: rtc: ac100: Assign .num before accessing .hws
Commit: 6bb55381daf1a1bed0657189a1396e7467712525
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6bb55381daf1a1bed0657189a1396e7467712525
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98848
Analysis date: Sat, 24 Oct 2026 12:55:28 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Late counted-by metadata initialization can trigger UBSAN during AC100 probe despite all stores remaining within the allocated array.

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

The original Linux kernel CVE announcement for CVE-2026-98848 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98848

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.

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

CVE-2026-98848	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98848 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-665;*CWE-457;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'The AC100 RTC clock registration path accesses clk_data hws while the __counted_by field clk_data num is still zero. The backing allocation already contains AC100_CLKOUT_NUM entries, so this is a sanitizer metadata initialization error rather than a real out of bounds write. With CONFIG_UBSAN_BOUNDS it produces a bounds report during device probe, and with CONFIG_UBSAN_TRAP the first store can trap and cause probe failure or a kernel oops. For the CVSS the PR:H value reflects that reliable retriggering normally requires administrative control over driver binding or device probing. There is no supported confidentiality impact, integrity impact, UAF, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.1 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	KASAN OOB SIMPLEFIX LINUS 	-	-	checked

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

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0 (+1 plausible trap/Oops, -1 specialized sanitizer/compiler configuration).
* Conservative score: 0; no floor or cap applied.
* Raw paranoid score: 0.
* Paranoid score: 0; stronger consequences are unsupported.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash/strong DoS: with `CONFIG_UBSAN_BOUNDS`, counted-by-aware compiler support, and `CONFIG_UBSAN_TRAP`, the first store can trap during device probe.
* -1 Non-default configuration: the fault requires a new compiler implementing `__counted_by` bounds checking plus UBSAN bounds instrumentation; trapping additionally requires `CONFIG_UBSAN_TRAP`.
* The backing allocation already has `AC100_CLKOUT_NUM` entries. Only the sanitizer's current logical bound is zero because `.num` is initialized late; no physical heap OOB write is shown.
* No UAF, retry accumulation, shared-backing write, authorization bypass, protected-state corruption, disclosure, or integrity primitive is present.
* B5-R does not apply: there is no heap/slab OOB write, retry accumulation, attacker-influenced retry sequence, or later consumption of corrupted state.
* Extra availability, C/I, and LPE points are not awarded.

3. Reachability analysis

The path runs while probing AC100 RTC hardware. No attacker-invocable data path or below-host-admin trigger is established. Administrative driver rebinding might retrigger probe, but the supplied source does not prove that this is the only trigger; therefore host-admin and UID-0 requirements remain unknown. No namespace capability, remote input, race, or prior attacker-controlled object setup is shown.

4. Primitive and severity reading

The exact defect is late initialization of counted-by metadata before valid in-allocation array stores. It can cause a sanitizer report or trap, but it does not write outside the allocated `hws[]` storage. This is CLASS_C configuration-dependent fault behavior, not memory corruption. The fix changes initialization order without changing successful provider behavior. ImportantCandidate is NO and automatic downgrade is allowed because no unresolved corruption or trust-boundary primitive remains.

5. One-sentence report phrase

Late counted-by metadata initialization can trigger UBSAN during AC100 probe despite all stores remaining within the allocated array.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch and commit explicitly establish a sanitizer metadata false positive rather than a real out-of-bounds access.

7. Call-site confidence

Call-site confidence: high

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

Patch: rtc: ac100: Assign .num before accessing .hws
Commit: 6bb55381daf1a1bed0657189a1396e7467712525
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6bb55381daf1a1bed0657189a1396e7467712525

Commit description:

Commit f316cdf ("clk: Annotate struct clk_hw_onecell_data with
__counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
about the number of elements in .hws[], so that it can warn when .hws[]
is accessed out of bounds. As noted in that change, the __counted_by
member must be initialized with the number of elements before the first
array access happens, otherwise there will be a warning from each access
prior to the initialization because the number of elements is zero.
This occurs in ac100_rtc_register_clks() due to .num being assigned only
after every clkout clock has been stored in .hws[]. With
CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
during probe, and with CONFIG_UBSAN_TRAP the first store traps.

Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was
allocated with, right after the allocation. That is the value the loop
counter ends up at on the success path anyway, so the provider's
behaviour is unchanged.

Cc: stable@vger.kernel.org
Fixes: f316cdf ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
Assisted-by: LLM
Signed-off-by: Aamir Ahmed <elb12345@hotmail.co.uk>
Reviewed-by: Chen-Yu Tsai <wens@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/AS8P251MB00013E724A77A355668B6CCEC8B42@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/rtc/rtc-ac100.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=6bb55381daf1a1bed0657189a1396e7467712525

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

The original Linux kernel CVE announcement for CVE-2026-98848 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98848

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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: 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).