tty/serial: atmel: use port->name as name in request_irq()

commit 9594b5be upstream.

I was puzzled while looking at /proc/interrupts and random things showed
up between reboots. This occurred more often but I realised it later. The
"correct" output should be:
|38:      11861  atmel-aic5   2 Level     ttyS0

but I saw sometimes
|38:       6426  atmel-aic5   2 Level     tty1

and accounted it wrongly as correct. This is use after free and the
former example randomly got the "old" pointer which pointed to the same
content. With SLAB_FREELIST_RANDOM and HARDENED I even got
|38:       7067  atmel-aic5   2 Level     E=Started User Manager for UID 0

or other nonsense.
As it turns out the tty, pointer that is accessed in atmel_startup(), is
freed() before atmel_shutdown(). It seems to happen quite often that the
tty for ttyS0 is allocated and freed while ->shutdown is not invoked. I
don't do anything special - just a systemd boot :)

Use dev_name(&pdev->dev) as the IRQ name for request_irq(). This exists
as long as the driver is loaded so no use-after-free here.

Cc: stable@vger.kernel.org
Fixes: 761ed4a9 ("tty: serial_core: convert uart_close to use tty_port_close")
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -1786,7 +1786,6 @@ static int atmel_startup(struct uart_port *port)
 {
 	struct platform_device *pdev = to_platform_device(port->dev);
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
-	struct tty_struct *tty = port->state->port.tty;
 	int retval;
 
 	/*
@@ -1801,8 +1800,8 @@ static int atmel_startup(struct uart_port *port)
 	 * Allocate the IRQ
 	 */
 	retval = request_irq(port->irq, atmel_interrupt,
-			IRQF_SHARED | IRQF_COND_SUSPEND,
-			tty ? tty->name : "atmel_serial", port);
+			     IRQF_SHARED | IRQF_COND_SUSPEND,
+			     dev_name(&pdev->dev), port);
 	if (retval) {
 		dev_err(port->dev, "atmel_startup - Can't get irq\n");
 		return retval;