phy: renesas: rcar-gen3-usb2: Fix sysfs interface of "role"

commit 4bd5ead8 upstream.

Since the role_store() uses strncmp(), it's possible to refer
out-of-memory if the sysfs data size is smaller than strlen("host").
This patch fixes it by using sysfs_streq() instead of strncmp().
Reported-by: Pavel Machek <pavel@denx.de>
Fixes: 9bb86777 ("phy: rcar-gen3-usb2: add sysfs for usb role swap")
Cc: <stable@vger.kernel.org> # v4.10+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/phy/renesas/phy-rcar-gen3-usb2.c

@@ -23,6 +23,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/regulator/consumer.h>
+#include <linux/string.h>
 #include <linux/usb/of.h>
 #include <linux/workqueue.h>
 
@@ -241,9 +242,9 @@ static ssize_t role_store(struct device *dev, struct device_attribute *attr,
 	if (!ch->has_otg_pins || !ch->phy->init_count)
 		return -EIO;
 
-	if (!strncmp(buf, "host", strlen("host")))
+	if (sysfs_streq(buf, "host"))
 		new_mode = PHY_MODE_USB_HOST;
-	else if (!strncmp(buf, "peripheral", strlen("peripheral")))
+	else if (sysfs_streq(buf, "peripheral"))
 		new_mode = PHY_MODE_USB_DEVICE;
 	else
 		return -EINVAL;