Subject: CVE-2023-52456: serial: imx: fix tx statemachine deadlock

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

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

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

serial: imx: fix tx statemachine deadlock

When using the serial port as RS485 port, the tx statemachine is used to
control the RTS pin to drive the RS485 transceiver TX_EN pin. When the
TTY port is closed in the middle of a transmission (for instance during
userland application crash), imx_uart_shutdown disables the interface
and disables the Transmission Complete interrupt. afer that,
imx_uart_stop_tx bails on an incomplete transmission, to be retriggered
by the TC interrupt. This interrupt is disabled and therefore the tx
statemachine never transitions out of SEND. The statemachine is in
deadlock now, and the TX_EN remains low, making the interface useless.

imx_uart_stop_tx now checks for incomplete transmission AND whether TC
interrupts are enabled before bailing to be retriggered. This makes sure
the state machine handling is reached, and is properly set to
WAIT_AFTER_SEND.

The Linux kernel CVE team has assigned CVE-2023-52456 to this issue.

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

	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 5.10.209 with commit 6e04a9d30509
	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 5.15.148 with commit ff168d4fdb0e
	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.1.75 with commit 63ee7be01a3f
	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.6.14 with commit 763cd6874631
	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.7.2 with commit 9a662d06c22d
	Issue introduced in 5.9 with commit cb1a60923609 and fixed in 6.8 with commit 78d60dae9a0c

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-2023-52456
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/tty/serial/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/6e04a9d30509fb53ba6df5d655ed61d607a7cfda
	https://git.kernel.org/stable/c/ff168d4fdb0e1ba35fb413a749b3d6cce918ec19
	https://git.kernel.org/stable/c/63ee7be01a3f7d28b1ea8b8d7944f12bb7b0ed06
	https://git.kernel.org/stable/c/763cd68746317b5d746dc2649a3295c1efb41181
	https://git.kernel.org/stable/c/9a662d06c22ddfa371958c2071dc350436be802b
	https://git.kernel.org/stable/c/78d60dae9a0c9f09aa3d6477c94047df2fe6f7b0