tty: serial: 8250: protect against NULL uart->port.dev in register

serial8250_register_8250_port() conditionally copies uart->port.dev
from up->port.dev only when up->port.dev is non-NULL:

	if (up->port.dev) {
		uart->port.dev = up->port.dev;
		...
	}

So if both the existing uart slot and up have a NULL ->dev,
uart->port.dev remains NULL. The very next ACPI companion check
then dereferences it unconditionally:

	if (!has_acpi_companion(uart->port.dev)) {

has_acpi_companion() reads dev->fwnode without a NULL guard
(include/linux/acpi.h), so this NULL-derefs the kernel for the
remaining no-dev case rather than just skipping the
mctrl_gpio_init() initialisation as intended.

smatch flags the inconsistency:

  drivers/tty/serial/8250/8250_core.c:767
  serial8250_register_8250_port() error: 'uart->port.dev' could be
  null (see line 719)

Guard the call with a NULL check so register continues to work
for callers that legitimately have no parent device (legacy
non-OF/non-ACPI registrations).

No functional change for callers that pass a non-NULL ->dev.

Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
Link: https://patch.msgid.link/20260508181237.11146-1-sozdayvek@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index a428e88938eb781d260a76a2e793d336d703c147..e136cec0c0be75ffa5be5e3ecb420db8fa84dcc8 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -764,7 +764,7 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
         * Only call mctrl_gpio_init(), if the device has no ACPI
         * companion device
         */
-       if (!has_acpi_companion(uart->port.dev)) {
+       if (uart->port.dev && !has_acpi_companion(uart->port.dev)) {
                struct mctrl_gpios *gpios = mctrl_gpio_init(&uart->port, 0);
                if (IS_ERR(gpios)) {
                        ret = PTR_ERR(gpios);