CVE-2026-74463: i2c: jz4780: Cache host clock rate at probe to prevent CCF prepare_lock deadlock

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

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

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

i2c: jz4780: Cache host clock rate at probe to prevent CCF prepare_lock deadlock

Fix a severe AB/BA deadlock between the Common Clock Framework (CCF)
and the I2C adapter lock, which triggers when an I2C-controlled clock
generator client (like the Si5351) is registered or modified under the CCF.

During an i2c client clock (generator) frequency change, the CCF acquires its global
'prepare_lock' mutex and the driver calls i2c_transfer() to update the client's
chip registers, stalling for the adapter's I2C bus lock.

Concurrently, an independent, parallel transfer on the same bus (e.g., a GPIO
expander handling LEDs) can hold the I2C adapter lock. Inside this parallel
transfer path, jz4780_i2c_set_speed() calls clk_get_rate() on the host
controller's input clock to calculate bus timings. This call attempts to acquire
the blocked CCF 'prepare_lock', creating a circular dependency that freezes
the system.

The jz4780 host controller clock itself is static and never changes at runtime.

However, calling clk_get_rate() inside the active transfer path introduces
an unnecessary dependency on the CCF internal locks.

Eliminate this synchronous clk_get_rate() call from the active transfer
path by caching the static host peripheral clock rate once - inside the private
jz4780_i2c structure during jz4780_i2c_probe(). Update jz4780_i2c_set_speed()
to use this cached value, safely decoupling active I2C transactions from the
CCF internal locks without any risk of stale timings.

Assisted-by web based Google AI (pinpointing the bug and writing the message).

The Linux kernel CVE team has assigned CVE-2026-74463 to this issue.


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

	Issue introduced in 4.1 with commit ba92222ed63a12d09120df9b92f56cc990abac19 and fixed in 6.6.151 with commit 14429dc1c756c35e106f01ff09cadccb82f5531d
	Issue introduced in 4.1 with commit ba92222ed63a12d09120df9b92f56cc990abac19 and fixed in 6.12.103 with commit b6cb47e186abba85a3b08aa3023067ab82577286
	Issue introduced in 4.1 with commit ba92222ed63a12d09120df9b92f56cc990abac19 and fixed in 6.18.44 with commit 19b783335d62e7a2367436a6e1f1b37da1878360
	Issue introduced in 4.1 with commit ba92222ed63a12d09120df9b92f56cc990abac19 and fixed in 7.1.8 with commit aa1944b52d6492c48bdd17046578aa0d953546e6
	Issue introduced in 4.1 with commit ba92222ed63a12d09120df9b92f56cc990abac19 and fixed in 7.2-rc6 with commit d99607c888f26e8a4e9fe9772860cef4aff86bb4

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-2026-74463
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/i2c/busses/i2c-jz4780.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/14429dc1c756c35e106f01ff09cadccb82f5531d
	https://git.kernel.org/stable/c/b6cb47e186abba85a3b08aa3023067ab82577286
	https://git.kernel.org/stable/c/19b783335d62e7a2367436a6e1f1b37da1878360
	https://git.kernel.org/stable/c/aa1944b52d6492c48bdd17046578aa0d953546e6
	https://git.kernel.org/stable/c/d99607c888f26e8a4e9fe9772860cef4aff86bb4