CVE-2026-74711: hwmon: (pmbus) Fix type confusion in notification logic

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

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

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

hwmon: (pmbus) Fix type confusion in notification logic

Sashiko reports:

At the start of the loop in pmbus_notify(), the code unconditionally casts
every attribute to a struct sensor_device_attribute:

drivers/hwmon/pmbus/pmbus_core.c:pmbus_notify() {
    for (i = 0; i < data->num_attributes; i++) {
        struct device_attribute *da = to_dev_attr(data->group.attrs[i]);
        struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
        int index = attr->index;
...
}

However, data->group.attrs can contain other types like struct
pmbus_samples_reg or struct pmbus_sensor, which only embed a base
struct device_attribute.

If da is a struct pmbus_samples_reg, dev_attr is the last member. Casting
it to struct sensor_device_attribute and reading the index field appears
to access memory past the end of the allocation, which might trigger a
slab-out-of-bounds read.

Additionally, if da is a struct pmbus_sensor, casting it causes the index
field to overlap with the page, phase, and reg fields. Could this produce
a garbage mask on little-endian systems that spuriously matches the target
reg, page, and flags during an alert?

Fix the problem by using struct sensor_device_attr in struct pmbus_sensor
and struct pmbus_label. Since those attributes never trigger a
notification, set the value of attr->index to -1 for them. Use this value
to distinguish from boolean attributes which _can_ trigger a notification
and use the index field to encode mask, page, and register values.

The Linux kernel CVE team has assigned CVE-2026-74711 to this issue.


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

	Issue introduced in 6.4 with commit f469bde9afd136598a0c4edc054296e6046f90ee and fixed in 6.18.45 with commit 821f6416e69782fa662aff94b5ea52c943042790
	Issue introduced in 6.4 with commit f469bde9afd136598a0c4edc054296e6046f90ee and fixed in 7.1.9 with commit 0b121de89a99c54bcf516999b04e8531c84f08d5
	Issue introduced in 6.4 with commit f469bde9afd136598a0c4edc054296e6046f90ee and fixed in 7.2 with commit 59bd68ab05a8f9c9a60b6ec44682084184803ff4

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-2026-74711
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/pmbus/pmbus_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/821f6416e69782fa662aff94b5ea52c943042790
	https://git.kernel.org/stable/c/0b121de89a99c54bcf516999b04e8531c84f08d5
	https://git.kernel.org/stable/c/59bd68ab05a8f9c9a60b6ec44682084184803ff4