serial: samsung: Fix possible out of bounds access on non-DT platform

commit 926b7b51 upstream.

On non-DeviceTree platforms, the index of serial device is a static
variable incremented on each probe.  It is incremented even if deferred
probe happens when getting the clock in s3c24xx_serial_init_port().

This index is used for referencing elements of statically allocated
s3c24xx_serial_ports array.  In case of re-probe, the index will point
outside of this array leading to memory corruption.

Increment the index only on successful probe.
Reported-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Fixes: b497549a ("[ARM] S3C24XX: Split serial driver into core and per-cpu drivers")
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/tty/serial/samsung.c

@@ -1307,8 +1307,6 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
 		ourport->info->fifosize :
 		ourport->drv_data->fifosize[probe_index];
 
-	probe_index++;
-
 	dbg("%s: initialising port %p...\n", __func__, ourport);
 
 	ret = s3c24xx_serial_init_port(ourport, pdev);
@@ -1344,6 +1342,8 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
 	if (ret < 0)
 		dev_err(&pdev->dev, "failed to add cpufreq notifier\n");
 
+	probe_index++;
+
 	return 0;
 
  probe_err: