CVE-2026-72142: i2c: imx: fix locked bus on SMBus block-read of 0 (atomic)

CVE-2026-72142: i2c: imx: fix locked bus on SMBus block-read of 0 (atomic)

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

i2c: imx: fix locked bus on SMBus block-read of 0 (atomic)

SMBus 3.1 6.5.7 allows a Block Read byte count of 0, but the atomic
(polling) path rejects it as -EPROTO. Worse, it returns without a
NACK+STOP: the next receive cycle has already started, so the target
keeps holding SDA and the bus stays stuck until a power cycle for
this i2c controller.

Reading I2DR to obtain the count likewise arms the next byte on the
count > I2C_SMBUS_BLOCK_MAX path, which also returned -EPROTO directly
and left the bus held.

Handle both: NACK the in-flight dummy byte (TXAK) and extend msgs->len so
the existing last-byte handling emits STOP; the dummy byte is discarded.
A count of 0 is a valid empty block read; a count above
I2C_SMBUS_BLOCK_MAX is still reported as -EPROTO, but only after the bus
has been released.

The interrupt-driven path has the same flaw from a later commit and is
fixed separately, as it carries a different Fixes: tag and stable range.

The Linux kernel CVE team has assigned CVE-2026-72142 to this issue.


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

	Issue introduced in 3.16 with commit 8e8782c71595a5ad29e234ce6b3d2fce787fb07a and fixed in 6.6.148 with commit 016ef0f6ca4bc9bf0330ac41bd2ea349759643e3
	Issue introduced in 3.16 with commit 8e8782c71595a5ad29e234ce6b3d2fce787fb07a and fixed in 6.12.101 with commit c882e8cc68fb993700dc21fd6e754001e6297934
	Issue introduced in 3.16 with commit 8e8782c71595a5ad29e234ce6b3d2fce787fb07a and fixed in 6.18.40 with commit 6d2c973926d0612360693bc559be2ffde836151b
	Issue introduced in 3.16 with commit 8e8782c71595a5ad29e234ce6b3d2fce787fb07a and fixed in 7.1.5 with commit 60ed00d46616a9232e42ea7a3e3c0273d7cf7543
	Issue introduced in 3.16 with commit 8e8782c71595a5ad29e234ce6b3d2fce787fb07a and fixed in 7.2-rc4 with commit cb2fc37857693b55909fb77dc2c87cfbc1cdc476

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-2026-72142
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-imx.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/016ef0f6ca4bc9bf0330ac41bd2ea349759643e3
	https://git.kernel.org/stable/c/c882e8cc68fb993700dc21fd6e754001e6297934
	https://git.kernel.org/stable/c/6d2c973926d0612360693bc559be2ffde836151b
	https://git.kernel.org/stable/c/60ed00d46616a9232e42ea7a3e3c0273d7cf7543
	https://git.kernel.org/stable/c/cb2fc37857693b55909fb77dc2c87cfbc1cdc476