Change login logo and link. logo.png goes in /child_theme/images/ directory

change_login_logo.php

/**
 * Change login logo
 * Max image width should be 320px
 * @link http://andrew.hedges.name/experiments/aspect_ratio/ 
 */
add_action('login_head',  'rgt_custom_dashboard_logo');
function rgt_custom_dashboard_logo() {
	echo '<style  type="text/css">
		.login h1 a {
			background-image:url('.get_stylesheet_directory_uri().'/images/logo.png)  !important;
			background-size: 320px 82px !important;
			width: 320px !important;
			height: 82px !important;
		}
	</style>';
}

// Change login link
add_filter('login_headerurl','loginpage_custom_link');
function loginpage_custom_link() {
	return get_site_url();
}