[PATCH 4.9 92/96] serial: arc_uart: Fix out-of-bounds access through DT alias

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

[ Upstream commit f9f5786987e81d166c60833edcb7d1836aa16944 ]

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+renesas@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serial/arc_uart.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/tty/serial/arc_uart.c
+++ b/drivers/tty/serial/arc_uart.c
@@ -596,6 +596,11 @@ static int arc_serial_probe(struct platf
 	if (dev_id < 0)
 		dev_id = 0;
 
+	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];
 	port = &uart->port;