Add static function to propose security settings

Close #3, see #4

MD_JAIL.php

@@ -38,6 +38,93 @@ final class MD_JAIL {
      */
     public string $memory_limit;
 
+    /**
+     * Static function providing an advisory on how to harden the php.ini or
+     * .user.ini.
+     *
+     * @param array{shell_access_whitelist: string[], sys_function_whitelist: string[], file_function_whitelist: string[], file_uploads: bool, allow_url_fopen: bool, max_input_vars: integer, max_input_nesting_level: integer, curl: bool} $requested_resources Requested resources.
+     *
+     * @return string
+     */
+    public static function check_server_setup(array $requested_resources):string {
+
+        # ini_set("open_basedir", __DIR__ . "/../../");
+
+        $disable_functions = [
+            "dl",                            # Loads a PHP extension at runtime
+            "opcache_get_status",            # Gets opcache status
+            "phpinfo",                       # For obvious reasons
+            "parse_ini_file",                # For obvious reasons
+            "show_source", "highlight_file", # Aliases; serve the content of a PHP file
+            "php_uname",                     # Returns information about the operating system PHP is running on
+            "phpcredits",                    # Credits page of PHP authors
+            "php_strip_whitespace",          # Return PHP source with stripped comments and whitespace
+            "popen", "pclose",               # Similar to fopen, but capable of shell access
+            "virtual",                       # Perform an Apache sub-request
+        ];
+
+        $disable_aliases = [
+            "ini_set"                 => "ini_alter",       # Alias of ini_set(), ini_set is preferred
+            "disk_free_space"         => "diskfreespace",   # Alias of disk_free_space()
+            "PHP_SAPI"                => "php_sapi_name",   # Alias of constant PHP_SAPI
+            "stream_set_write_buffer" => "set_file_buffer", # Alias of stream_set_write_buffer()
+        ];
+
+        $shell_access_functions = array_diff(["exec", "passthru", "proc_close", "proc_get_status", "proc_nice", "proc_open", "proc_terminate", "shell_exec", "system"], $requested_resources['shell_access_whitelist']);
+        $sys_functions = array_diff(["get_current_user", "getmyuid", "getmygid", "getmypid", "getmyinode", "getlastmod", "getenv", "putenv"], $requested_resources['sys_function_whitelist']);
+        $file_functions = array_diff(["chgrp", "chgrp", "lchgrp", "lchown", "link", "linkinfo", "symlink"], $requested_resources['file_function_whitelist']);
+
+        if ($requested_resources['curl'] === false) {
+            $disable_functions[] = "curl_init";
+            $disable_functions[] = "curl_exec";
+            $disable_functions[] = "curl_multi_init";
+            $disable_functions[] = "curl_multi_exec";
+        }
+
+        $disabledWOAliases = array_merge($disable_functions, $shell_access_functions, $sys_functions, $file_functions);
+
+        $output = '## php.ini' . PHP_EOL . PHP_EOL;
+        $output .= PHP_EOL . "php_value[disable_functions] = \"" . implode(", ", array_merge($disabledWOAliases, $disable_aliases)) . "\"";
+
+        if ($requested_resources['file_uploads'] === false) {
+            $output .= PHP_EOL . "php_value[file_uploads] = 0";
+        }
+        if ($requested_resources['allow_url_fopen'] === false) {
+            $output .= PHP_EOL . "php_value[allow_url_fopen] = 0";
+        }
+
+        $output .= PHP_EOL . PHP_EOL . '## .user.ini' . PHP_EOL;
+
+        if ($requested_resources['file_uploads'] === false) {
+            $output .= PHP_EOL . "php_value[upload_max_filesize] = 1";
+        }
+        if ($requested_resources['max_input_vars'] != ini_get("max_input_vars")) {
+            $output .= PHP_EOL . "php_value[max_input_vars] = " . $requested_resources['max_input_vars'];
+        }
+        if ($requested_resources['max_input_nesting_level'] != ini_get("max_input_nesting_level")) {
+            $output .= PHP_EOL . "php_value[max_input_nesting_level] = " . $requested_resources['max_input_nesting_level'];
+        }
+
+        $output .= PHP_EOL . PHP_EOL . '## PHPStan Directives' . PHP_EOL . PHP_EOL . "    disallowedFunctionCalls:" . PHP_EOL;
+        foreach ($disable_aliases as $to_keep => $disabled) {
+
+            $output .= '
+    -
+        function: \'' . $disabled . '()\'
+        message: \'use ' . $to_keep . ' instead\'';
+
+        }
+        foreach ($disabledWOAliases as $disabled) {
+
+            $output .= '
+    - function: \'' . $disabled . '()\'';
+
+        }
+
+        return $output;
+
+    }
+
     /**
      * Registers an additional accessible directory for open_basedir.
      *
@@ -87,6 +174,7 @@ final class MD_JAIL {
      * Applies basedir restrictions.
      *
      * @return void
+     */
      private function _apply_basedir_restriction():void {
 
         if (empty($this->_open_basedir)) {
@@ -97,7 +185,6 @@ final class MD_JAIL {
         }
 
      }
-     */
 
     /**
      * Enforces security options previously set.
@@ -124,7 +211,7 @@ final class MD_JAIL {
         $this->_apply_time_limit();
 
         // Set accessible file paths
-        // $this->_apply_basedir_restriction();
+        $this->_apply_basedir_restriction();
 
         $this->_status = self::STATUS_SPECIFIED;
         $this->__destruct();