[PATCH v3] tty/serial: atmel: use port->name as name in request_irq()

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rob Herring <robh@kernel.org>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Peter Hurley <peter@hurleysoftware.com>,
	Richard Genoud <richard.genoud@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
	Jiri Slaby <jslaby@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>
Subject: [PATCH v3] tty/serial: atmel: use port->name as name in request_irq()
Date: Mon, 7 May 2018 19:11:30 +0200	[thread overview]
Message-ID: <20180507171130.iba7nm3tgfyxgabs@linutronix.de> (raw)
In-Reply-To: <CAL_JsqJ+84OFyN07XWsb0hSHxtxL_V6gSfO+iMSOU1bceztr3Q@mail.gmail.com>

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: 761ed4a94582 ("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>
---
v2…v3: - Add Acked-by
       - replace port->name -> dev_name(&pdev->dev) to ease work for
	 backporters (suggested by Rob)
v1…v2: add Fixes after bisect.

 drivers/tty/serial/atmel_serial.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index e287fe8f10fc..55b3eff148b1 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1757,7 +1757,6 @@ 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;
 
 	/*
@@ -1772,8 +1771,8 @@ 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;
-- 
2.17.0


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