[PATCH 3.16 018/366] serial: arc_uart: Fix out-of-bounds access through DT alias

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Geert Uytterhoeven <geert+rene...@glider.be>

commit f9f5786987e81d166c60833edcb7d1836aa16944 upstream.

The arc_uart_ports[] array is indexed using a value derived from the
"serialN" alias in DT, which may lead to an out-of-bounds access.

Fix this by adding a range check.

Note that the array size is defined by a Kconfig symbol
(CONFIG_SERIAL_ARC_NR_PORTS), so this can even be triggered using a
legitimate DTB.

Fixes: ea28fd56fcde69af ("serial/arc-uart: switch to devicetree based probing")
Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
[bwh: Backported to 3.16: Put the check in arc_uart_init_one() and move
 initialisation of the uart variable below it]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/drivers/tty/serial/arc_uart.c
+++ b/drivers/tty/serial/arc_uart.c
@@ -531,8 +531,14 @@ arc_uart_init_one(struct platform_device
 {
        struct resource *res, *res2;
        unsigned long *plat_data;
-       struct arc_uart_port *uart = &arc_uart_ports[dev_id];
+       struct arc_uart_port *uart;
 
+       if (dev_id >= ARRAY_SIZE(arc_uart_ports)) {
+               dev_err(&pdev->dev, "serial%d out of range\n", dev_id);
+               return -EINVAL;
+       }
+
+       uart = &arc_uart_ports[dev_id];
        plat_data = dev_get_platdata(&pdev->dev);
        if (!plat_data)
                return -ENODEV;