usb: gadget: udc: renesas_usb3: Fix sysfs interface of "role"

commit 5dac665c 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().

Fixes: cc995c9e ("usb: gadget: udc: renesas_usb3: add support for usb role swap")
Cc: <stable@vger.kernel.org> # v4.12+
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/renesas_usb3.c

@@ -19,6 +19,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
+#include <linux/string.h>
 #include <linux/sys_soc.h>
 #include <linux/uaccess.h>
 #include <linux/usb/ch9.h>
@@ -2378,9 +2379,9 @@ static ssize_t role_store(struct device *dev, struct device_attribute *attr,
 	if (usb3->forced_b_device)
 		return -EBUSY;
 
-	if (!strncmp(buf, "host", strlen("host")))
+	if (sysfs_streq(buf, "host"))
 		new_mode_is_host = true;
-	else if (!strncmp(buf, "peripheral", strlen("peripheral")))
+	else if (sysfs_streq(buf, "peripheral"))
 		new_mode_is_host = false;
 	else
 		return -EINVAL;