[CVE-2026-74546][LOW] hwmon: (adt7470) Fix divide-by-zero TOCTOU crash in fan speed read [ Upstream

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

CVE: CVE-2026-74546
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: hwmon: (adt7470) Fix divide-by-zero TOCTOU crash in fan speed read [ Upstream
Commit: d328175045176f85c15c369bd21dc551351e7935
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d328175045176f85c15c369bd21dc551351e7935
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74546
Analysis date: Sat, 15 Aug 2026 13:14:41 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A TOCTOU race in the ADT7470 hwmon fan read path can let a local user trigger a divide-by-zero kernel crash when cached fan data changes to zero between validation and RPM conversion.

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

The original Linux kernel CVE announcement for CVE-2026-74546 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74546

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-2026-74546	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-369;CWE-367;CWE-362;BEST CVSS score: '4.7';DESCR 'adt7470_fan_read() has a TOCTOU race because the cached fan value can be checked once and then read again during RPM conversion. If a concurrent device update changes the cached fan period to zero between these two reads, FAN_PERIOD_TO_RPM() can divide by zero and crash the kernel. For the CVSS the PR:L is used because a local user or local process can typically trigger hwmon sysfs reads, but the issue still requires local code execution and a system with the adt7470 driver and hardware present. The issue is not network reachable. Impact is denial of service via kernel crash. No credible confidentiality or integrity impact is indicated because the primitive is divide by zero rather than memory corruption.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DANGER RACE UAF KERNEL_PANIC_PLUS_UAF HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  hwmon fan input attributes are commonly readable by local users through sysfs, so a local process may be able to trigger repeated reads.

* Reliable kernel crash / strong DoS: +1
  The described failure mode is a divide-by-zero in `FAN_PERIOD_TO_RPM()`, which can crash the kernel.

Negative signals:

* Hard or unreliable race / special timing required: -1
  The bug requires the cached fan value to become zero between validation and conversion.

* Physical-only or rare hardware-only condition: -2 conservative
  The issue requires the `adt7470` hwmon driver and compatible hardware or platform exposure.

Paranoid adjustment:

* For the paranoid score, the hardware rarity penalty is treated as -1 instead of -2 because sysfs access to the affected read path is straightforward once the driver and hardware are present.

No memory corruption signals apply. This is divide-by-zero DoS, not UAF, OOB write, type confusion, refcount misuse, or page-cache corruption.

## 3. Reachability analysis

A local user or local process can potentially trigger the read path if the affected hwmon sysfs attributes are exposed and readable. No network reachability is present. Containers do not generally improve reachability unless the host exposes the relevant hwmon sysfs entries into the container. The path is hardware and driver dependent, so exposure is limited to systems using the ADT7470-compatible monitoring device.

Call-site confidence: high. The changed code is directly in the fan read handler.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS. The theoretical impact is limited to kernel crash by divide-by-zero. There is no realistic evidence of privilege escalation, confidentiality impact, integrity impact, or memory corruption. The race makes triggering less reliable, and the required hardware significantly limits exposure.

## 5. One-sentence report phrase

A TOCTOU race in the ADT7470 hwmon fan read path can let a local user trigger a divide-by-zero kernel crash when cached fan data changes to zero between validation and RPM conversion.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed in most triage workflows because it is hardware-specific, local-only, race-dependent, and shows DoS-only impact without a memory corruption or privilege-escalation primitive.

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

Patch: hwmon: (adt7470) Fix divide-by-zero TOCTOU crash in fan speed read [ Upstream
Commit: d328175045176f85c15c369bd21dc551351e7935
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d328175045176f85c15c369bd21dc551351e7935

Changed files:
  drivers/hwmon/adt7470.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=d328175045176f85c15c369bd21dc551351e7935

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

The original Linux kernel CVE announcement for CVE-2026-74546 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74546

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 1

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).