SQL exploit

Note that I fixed up some other parts that aren’t related to the exploit. The UPDATE query wasn’t valid, since your table doesn’t have a ‘count’ column, and it didn’t seem worth it to do the SELECT statement, and then decide what to do with the DELETE/INSERT statements, when you can run the DELETE and INSERT *IGNORE* (that’s the key part).

Oh note, that I removed the id column from the table, since that also isn’t used, and just takes up space in the database. I made the unique id for the database both remaining fields, which is nice, since you don’t ever want a user to be able to vote twice on a post anyway.

That is better.

There is a $postid = $postid, which I’m not sure what you think that is doing.

The unused id column is still there in the database.

Why do you hook with a nopriv ajax call, when you depend on the user being logged in?

The basic idea of your plugin is good, and I’m using it on an active site, but I rewrote it because I didn’t need as much functionality, and made the code a lot simpler.

Here is the javascript I use in the theme:

jQuery('body').on('click', '.made_it > a', function(){
                        var $madeit = jQuery(this).parent();
                        jQuery.ajax({
                                type: 'POST',
                                url: admin_ajax_url,
                                data: {action: "jondaley_like_post_insert", postid: $madeit.attr('postid')},
                                success: function(data){
                                        $madeit.find('.count').html(data);
                                }
                        });
                        return false;
                });

And here is the only file in the plugin directory:

define('JONDALEY_LIKE_POST_PLUGIN_PATH', WP_PLUGIN_URL . '/' . plugin_basename( dirname(__FILE__) ) . '/' );

register_activation_hook(__FILE__, jondaley_like_post_install());
register_uninstall_hook(__FILE__, jondaley_like_post_drop());
function jondaley_like_post_install() {
    global $wpdb;
        $sql = "CREATE TABLE IF NOT EXISTS " . $wpdb->prefix . "jondaley_like_post_info ".
                "(UNIQUE KEY vote (postid, userid), ".
                "postid  bigint(20) NOT NULL, ".
                "userid  bigint(20) NOT NULL, ".
                "like_date timestamp NOT NULL DEFAULT NOW())";
        $wpdb->query($sql);
}

function jondaley_like_post_drop() {
        if(get_option('jondaley_like_post_deletion') == 1){
                global $wpdb;
                $table = $wpdb->prefix . "jondaley_like_post_info";
                $wpdb->query('DROP TABLE IF EXISTS ' . $wpdb->prefix . 'jondaley_like_post_info');
        }
}

function jondaley_like_post_get_vote($postid, $userid){
        $num_votes = 0;

        global $wpdb;
        $table = $wpdb->prefix . "jondaley_like_post_info";

        $results = $wpdb->get_results($wpdb->prepare("SELECT count(postid) AS count FROM $table WHERE postid=%d AND userid=%d", $postid, $userid), ARRAY_A);
        if(isset($results[0]['count']))
                $num_votes = $results[0]['count'];

        return $num_votes;
}

function jondaley_like_post_get_votes($postid){
        global $wpdb;
        $table = $wpdb->prefix . "jondaley_like_post_info";

        $results = $wpdb->get_results($wpdb->prepare("SELECT count(postid) AS count FROM $table WHERE postid=%d", $postid), ARRAY_A);
        $count = $results[0]['count'];
        if(is_numeric($count))
                return $count + 1;
        return 1;
}

// get avatars of 10 people who voted for this post
function jondaley_like_post_who_voted($postid){
        global $wpdb;
        $avatars = '';

        $table = $wpdb->prefix . "jondaley_like_post_info";
        $result = $wpdb->get_results($wpdb->prepare("SELECT userid FROM $table WHERE postid=%d LIMIT 10", $postid), ARRAY_A);
        $total_user = $wpdb->num_rows;
        for($i=0; $i <$total_user ; $i++){
                $avatars .= get_avatar($result[$i]['userid'], 100);
        }
        return $avatars;
}

// AJAX function, it's okay to access get_current_user_id() here
function jondaley_like_post_insert(){
        $postid = (int)$_POST['postid'];
        if(!$postid)
                die('Error');

        $userid = get_current_user_id();
    global $wpdb;
    $table = $wpdb->prefix . "jondaley_like_post_info";

        if(jondaley_like_post_get_vote($postid, $userid))
                $wpdb->query($wpdb->prepare("DELETE FROM $table WHERE postid=%d AND userid=%d", $postid, $userid));
        else
                $wpdb->query($wpdb->prepare("INSERT IGNORE INTO $table (postid, userid) VALUES(%d, %d)", $postid, $userid));
        print jondaley_like_post_get_votes($postid);
        die;
}
add_action('wp_ajax_jondaley_like_post_insert', 'jondaley_like_post_insert');

So, you can see, a lot of it is the same (I don’t use the avatar, so I haven’t checked that).

I did add a time field, because I need to be able to sort the likes by date, and show the most recent likes on the home page.