usb: gadget: eliminate NULL pointer dereference (bugfix)

usb: gadget: eliminate NULL pointer dereference (bugfix)

This patch fixes a bug which causes NULL pointer dereference in
ffs_ep0_ioctl. The bug happens when the FunctionFS is not bound (either
has not been bound yet or has been bound and then unbound) and can be
reproduced with running the following commands:

$ insmod g_ffs.ko
$ mount -t functionfs func /dev/usbgadget
$ ./null

where null.c is:

#include <fcntl.h>
#include <linux/usb/functionfs.h>

int main(void)
{
	int fd = open("/dev/usbgadget/ep0", O_RDWR);
	ioctl(fd, FUNCTIONFS_CLEAR_HALT);

	return 0;
}
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: stable@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/f_fs.c

@@ -712,7 +712,7 @@ static long ffs_ep0_ioctl(struct file *file, unsigned code, unsigned long value)
 	if (code == FUNCTIONFS_INTERFACE_REVMAP) {
 		struct ffs_function *func = ffs->func;
 		ret = func ? ffs_func_revmap_intf(func, value) : -ENODEV;
-	} else if (gadget->ops->ioctl) {
+	} else if (gadget && gadget->ops->ioctl) {
 		ret = gadget->ops->ioctl(gadget, code, value);
 	} else {
 		ret = -ENOTTY;