[PATCH] serial: mxs-auart: Fix potential infinite loop

[Anton Vasilyev <vasilyev@ispras.ru>]

On the error path of mxs_auart_request_gpio_irq() is performed
backward iterating with index i of enum type. Underline enum type
may be unsigned char. In this case check (--i >= 0) will be always
true and error handling goes into infinite loop.

The patch changes type of index variable to int.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Anton Vasilyev <vasilyev@ispras.ru>
---
 drivers/tty/serial/mxs-auart.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 76aa289652f7..89b34bb09cde 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -1617,7 +1617,7 @@ static void mxs_auart_free_gpio_irq(struct mxs_auart_port *s)
 static int mxs_auart_request_gpio_irq(struct mxs_auart_port *s)
 {
 	int *irq = s->gpio_irq;
-	enum mctrl_gpio_idx i;
+	int i;
 	int err = 0;
 
 	for (i = 0; (i < UART_GPIO_MAX) && !err; i++) {
@@ -1634,8 +1634,9 @@ static int mxs_auart_request_gpio_irq(struct mxs_auart_port *s)
 
 	/*
 	 * If something went wrong, rollback.
+	 * Be careful: i may be unsigned.
 	 */
-	while (err && (--i >= 0))
+	while (err && (i-- > 0))
 		if (irq[i] >= 0)
 			free_irq(irq[i], s);
 
-- 
2.18.0