MDL-66732 core: improve detection of non-public sites.

lib/classes/ip_utils.php

@@ -245,4 +245,22 @@ final class ip_utils {
         return false;
     }
 
+    /**
+     * Return IP address for given hostname, or null on failure
+     *
+     * @param string $hostname
+     * @return string|null
+     */
+    public static function get_ip_address(string $hostname): ?string {
+        if (self::is_domain_name($hostname)) {
+            $address = gethostbyname($hostname);
+
+            // If address is different from hostname, we have success.
+            if (strcasecmp($address, $hostname) !== 0) {
+                return $address;
+            }
+        }
+
+        return null;
+    }
 }

lib/moodlelib.php

@@ -10444,6 +10444,8 @@ function site_is_public() {
         $ispublic = false;
     } else if (\core\ip_utils::is_ip_address($host) && !ip_is_public($host)) {
         $ispublic = false;
+    } else if (($address = \core\ip_utils::get_ip_address($host)) && !ip_is_public($address)) {
+        $ispublic = false;
     } else {
         $ispublic = true;
     }