serial: samsung: Fix ERR pointer dereference on deferred probe

commit e51e4d8a upstream.

When the clk_get() of "uart" clock returns EPROBE_DEFER, the next re-probe
finishes with success but uses invalid (ERR_PTR) values.  This leads to
dereferencing of ERR_PTR stored under ourport->clk:

	12c30000.serial: Controller clock not found
	(...)
	12c30000.serial: ttySAC3 at MMIO 0x12c30000 (irq = 61, base_baud = 0) is a S3C6400/10
	Unable to handle kernel paging request at virtual address fffffdfb

	(clk_prepare) from [<c039f7d0>] (s3c24xx_serial_pm+0x20/0x128)
	(s3c24xx_serial_pm) from [<c0395414>] (uart_change_pm+0x38/0x40)
	(uart_change_pm) from [<c039689c>] (uart_add_one_port+0x31c/0x44c)
	(uart_add_one_port) from [<c03a035c>] (s3c24xx_serial_probe+0x2a8/0x418)
	(s3c24xx_serial_probe) from [<c03ee110>] (platform_drv_probe+0x50/0xb0)
	(platform_drv_probe) from [<c03ecb44>] (driver_probe_device+0x1f4/0x2b0)
	(driver_probe_device) from [<c03eb0c0>] (bus_for_each_drv+0x44/0x8c)
	(bus_for_each_drv) from [<c03ec8c8>] (__device_attach+0x9c/0x100)
	(__device_attach) from [<c03ebf54>] (bus_probe_device+0x84/0x8c)
	(bus_probe_device) from [<c03ec388>] (deferred_probe_work_func+0x60/0x8c)
	(deferred_probe_work_func) from [<c012fee4>] (process_one_work+0x120/0x328)
	(process_one_work) from [<c0130150>] (worker_thread+0x2c/0x4ac)
	(worker_thread) from [<c0135320>] (kthread+0xd8/0xf4)
	(kthread) from [<c0107978>] (ret_from_fork+0x14/0x3c)

The first unsuccessful clk_get() causes s3c24xx_serial_init_port() to
exit with failure but the s3c24xx_uart_port is left half-configured
(e.g. port->mapbase is set, clk contains ERR_PTR).  On next re-probe,
the function s3c24xx_serial_init_port() will exit early with success
because of configured port->mapbase and driver will use old values,
including the ERR_PTR as clock.

Fix this by cleaning the port->mapbase on error path so each re-probe
will initialize all of the port settings.

Fixes: 60e93575 ("serial: samsung: enable clock before clearing pending interrupts during init")
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: driver doesn't set up DMA here]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/tty/serial/samsung.c

@@ -1163,7 +1163,7 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 		return -ENODEV;
 
 	if (port->mapbase != 0)
-		return 0;
+		return -EINVAL;
 
 	/* setup info for port */
 	port->dev	= &platdev->dev;
@@ -1213,14 +1213,15 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 	if (IS_ERR(ourport->clk)) {
 		pr_err("%s: Controller clock not found\n",
 				dev_name(&platdev->dev));
-		return PTR_ERR(ourport->clk);
+		ret = PTR_ERR(ourport->clk);
+		goto err;
 	}
 
 	ret = clk_prepare_enable(ourport->clk);
 	if (ret) {
 		pr_err("uart: clock failed to prepare+enable: %d\n", ret);
 		clk_put(ourport->clk);
-		return ret;
+		goto err;
 	}
 
 	/* Keep all interrupts masked and cleared */
@@ -1236,7 +1237,12 @@ static int s3c24xx_serial_init_port(struct s3c24xx_uart_port *ourport,
 
 	/* reset the fifos (and setup the uart) */
 	s3c24xx_serial_resetport(port, cfg);
+
 	return 0;
+
+err:
+	port->mapbase = 0;
+	return ret;
 }
 
 #ifdef CONFIG_SAMSUNG_CLOCK