CVE-2026-74549: hwmon: (nct6775-core) Prevent access to unsupported weight registers

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

hwmon: (nct6775-core) Prevent access to unsupported weight registers

Sashiko reports:

During initialization of the nct6116 chip, the driver sets data->pwm_num
to 5. However, it assigns several NCT6106 register arrays (such as
NCT6106_REG_WEIGHT_DUTY_STEP, NCT6106_REG_WEIGHT_TEMP_SEL, and
NCT6106_REG_WEIGHT_TEMP_*) to data->REG_PWM and data->REG_WEIGHT_TEMP.
These arrays only contain 3 elements.

In nct6775_update_pwm(), the driver iterates up to data->pwm_num. If
data->has_pwm has bits 3 or 4 set (which is structurally possible for
nct6116), the loop attempts to read elements at index 3 and 4 from these
3-element arrays. This results in a global out-of-bounds read, which can
be caught by KASAN.

Furthermore, the driver uses these garbage out-of-bounds values as
hardware register addresses for subsequent read and write operations. This
leads to invalid hardware register access, potentially causing hardware
misconfiguration or system crashes.

The underlying problem is that the chip does support up to five fan
control channels, but only the first three support weight control.
Fix the problem by extending the affected weight register arrays with
zeroed fields. The driver uses zeroed register addresses to determine
if a register is supported or not, and skips accesses for unsupported
registers.

The Linux kernel CVE team has assigned CVE-2026-74549 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.4 with commit 29c7cb485b321c024dedc168bcbb04451176b163 and fixed in 6.6.151 with commit 25b528816f5d83be5236dc182692369e8c9402b0
	Issue introduced in 5.4 with commit 29c7cb485b321c024dedc168bcbb04451176b163 and fixed in 6.12.103 with commit 689082a4cb166a7ae9729f7b12339e69fdad6c52
	Issue introduced in 5.4 with commit 29c7cb485b321c024dedc168bcbb04451176b163 and fixed in 6.18.44 with commit 1b722740ac5c2b2070f9ba922f4e0f227faf0246
	Issue introduced in 5.4 with commit 29c7cb485b321c024dedc168bcbb04451176b163 and fixed in 7.1.8 with commit 4ad2972ef0e1bd1018ad7a72661a4636ed7daecc
	Issue introduced in 5.4 with commit 29c7cb485b321c024dedc168bcbb04451176b163 and fixed in 7.2-rc6 with commit d0b704e569ac3b8416d8e02270cdc9bf830ed395

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74549
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/hwmon/nct6775-core.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/25b528816f5d83be5236dc182692369e8c9402b0
	https://git.kernel.org/stable/c/689082a4cb166a7ae9729f7b12339e69fdad6c52
	https://git.kernel.org/stable/c/1b722740ac5c2b2070f9ba922f4e0f227faf0246
	https://git.kernel.org/stable/c/4ad2972ef0e1bd1018ad7a72661a4636ed7daecc
	https://git.kernel.org/stable/c/d0b704e569ac3b8416d8e02270cdc9bf830ed395