CodeIginter 安全類源代碼分析

一、構造函數：

首先判斷CSRF保護是否開啓，若開啓，則初始化CSRF配置，然後添加cookie prefix前綴，最後設置CSRF hash：

public function __construct()
	{
		// Is CSRF protection enabled?
		if (config_item('csrf_protection') === TRUE)
		{
			// CSRF config
			foreach (array('csrf_expire', 'csrf_token_name', 'csrf_cookie_name') as $key)
			{
				if (FALSE !== ($val = config_item($key)))
				{
					$this->{'_'.$key} = $val;
				}
			}

			// Append application specific cookie prefix
			if (config_item('cookie_prefix'))
			{
				$this->_csrf_cookie_name = config_item('cookie_prefix').$this->_csrf_cookie_name;
			}

			// Set the CSRF hash
			$this->_csrf_set_hash();
		}

		log_message('debug', "Security Class Initialized");
	}

其中_csrf_set_hash()方法是設置CSRF保護cookie，首先判斷_csrf_cookie_name是否設置（即在config.php中設置），且是否被正則表達式匹配，則$this->_csrf_hash = $_COOKIE[$this->_csrf_cookie_name];否則$this->_csrf_hash = md5(uniqid(rand(), TRUE));

protected function _csrf_set_hash()
	{
		if ($this->_csrf_hash == '')
		{
			// If the cookie exists we will use it's value.
			// We don't necessarily want to regenerate it with
			// each page load since a page could contain embedded
			// sub-pages causing this feature to fail
			if (isset($_COOKIE[$this->_csrf_cookie_name]) &&
				preg_match('#^[0-9a-f]{32}$#iS', $_COOKIE[$this->_csrf_cookie_name]) === 1)
			{
				return $this->_csrf_hash = $_COOKIE[$this->_csrf_cookie_name];
			}

			return $this->_csrf_hash = md5(uniqid(rand(), TRUE));
		}

		return $this->_csrf_hash;
	}

二、驗證CSRF保護

首先判斷是不是POST請求，如果不是POST請求則調用$this->csrf_set_cookie()設置CSRF cookie，然後判斷token和cookie是否存在，再判斷POST過來的_csrf_token_name和cookies中的_csrf_cookie_name是否相等，否則顯示錯誤頁面，然後立即unset($_POST[$this->_csrf_token_name]);和unset($_COOKIE[$this->_csrf_cookie_name]);

public function csrf_verify()
	{
		// If it's not a POST request we will set the CSRF cookie
		if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
		{
			return $this->csrf_set_cookie();
		}

		// Do the tokens exist in both the _POST and _COOKIE arrays?
		if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]))
		{
			$this->csrf_show_error();
		}

		// Do the tokens match?
		if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
		{
			$this->csrf_show_error();
		}

		// We kill this since we're done and we don't want to
		// polute the _POST array
		unset($_POST[$this->_csrf_token_name]);

		// Nothing should last forever
		unset($_COOKIE[$this->_csrf_cookie_name]);
		$this->_csrf_set_hash();
		$this->csrf_set_cookie();

		log_message('debug', 'CSRF token verified');

		return $this;
	}

csrf_set_cookie()代碼如下：

public function csrf_set_cookie()
	{
		$expire = time() + $this->_csrf_expire;
		$secure_cookie = (config_item('cookie_secure') === TRUE) ? 1 : 0;

		if ($secure_cookie && (empty($_SERVER['HTTPS']) OR strtolower($_SERVER['HTTPS']) === 'off'))
		{
			return FALSE;
		}

		setcookie($this->_csrf_cookie_name, $this->_csrf_hash, $expire, config_item('cookie_path'), config_item('cookie_domain'), $secure_cookie);

		log_message('debug', "CRSF cookie Set");

		return $this;
	}

三、xss_clean()：對數據進行過濾，函數原型：public function xss_clean($str, $is_image = FALSE)，傳入需要過濾的字符串

該函數分以下幾個步驟過濾字符串：

①判斷字符串是否爲數組，則遞歸調用xss_clean()過濾

if (is_array($str))
		{
			while (list($key) = each($str))
			{
				$str[$key] = $this->xss_clean($str[$key]);
			}

			return $str;
		}

②：去除ASCII字符之間插入的空字符，如java\0script

$str = remove_invisible_characters($str);

③：驗證URL實體：調用私有方法$str = $this->_validate_entities($str);

protected function _validate_entities($str)
	{
		/*
		 * Protect GET variables in URLs
		 */

		 // 901119URL5918AMP18930PROTECT8198

		$str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', $this->xss_hash()."\\1=\\2", $str);

		/*
		 * Validate standard character entities
		 *
		 * Add a semicolon if missing.  We do this to enable
		 * the conversion of entities to ASCII later.
		 *
		 */
		$str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str);

		/*
		 * Validate UTF16 two byte encoding (x00)
		 *
		 * Just as above, adds a semicolon if missing.
		 *
		 */
		$str = preg_replace('#(&\#x?)([0-9A-F]+);?#i',"\\1\\2;",$str);

		/*
		 * Un-Protect GET variables in URLs
		 */
		$str = str_replace($this->xss_hash(), '&', $str);

		return $str;
	}

④：對已編碼的URL字符串進行解碼：

$str = rawurldecode($str);

⑤：轉換字符實體爲ASCII：使用preg_replace_callback調用回調函數_convert_attribute和_decode_entity

$str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array($this, '_convert_attribute'), $str);

$str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array($this, '_decode_entity'), $str);

其中_convert_attribute函數將匹配到的部分的'<'，'>'，'\\'轉換爲'>', '<', '\\\\'

protected function _convert_attribute($match)
	{
		return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);
	}

_decode_entity函數調用成員函數entity_decode進行實體解碼

public function entity_decode($str, $charset='UTF-8')
	{
		if (stristr($str, '&') === FALSE)
		{
			return $str;
		}

		$str = html_entity_decode($str, ENT_COMPAT, $charset);
		$str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str);
		return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
	}

⑥：再一次去除ASCII字符之間插入的空字符，如java\0script

$str = remove_invisible_characters($str);

⑦：將tabs轉換成' '

if (strpos($str, "\t") !== FALSE)
		{
			$str = str_replace("\t", ' ', $str);
		}

⑧：去除不允許的字符：

$str = $this->_do_never_allowed($str);

⑨：去除PHP標籤：

if ($is_image === TRUE)
		{
			// Images have a tendency to have the PHP short opening and
			// closing tags every so often so we skip those and only
			// do the long opening tags.
			$str = preg_replace('/<\?(php)/i', "<?\\1", $str);
		}
		else
		{
			$str = str_replace(array('<?', '?'.'>'),  array('<?', '?>'), $str);
		}

⑩：將字符串中的類似j a v a s c r i p t轉換爲javascript

$words = array(
			'javascript', 'expression', 'vbscript', 'script', 'base64',
			'applet', 'alert', 'document', 'write', 'cookie', 'window'
		);

		foreach ($words as $word)
		{
			$temp = '';

			for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++)
			{
				$temp .= substr($word, $i, 1)."\s*";
			}

			// We only want to do this when it is followed by a non-word character
			// That way valid stuff like "dealer to" does not become "dealerto"
			$str = preg_replace_callback('#('.substr($temp, 0, -3).')(\W)#is', array($this, '_compact_exploded_words'), $str);
		}

⒒刪除無效的javascript鏈接和img標籤

do
		{
			$original = $str;

			if (preg_match("/<a/i", $str))
			{
				$str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array($this, '_js_link_removal'), $str);
			}

			if (preg_match("/<img/i", $str))
			{
				$str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", array($this, '_js_img_removal'), $str);
			}

			if (preg_match("/script/i", $str) OR preg_match("/xss/i", $str))
			{
				$str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str);
			}
		}
		while($original != $str);

		unset($original);

12.清除一些屬性：style, onclick and xmlns

$str = $this->_remove_evil_attributes($str, $is_image);

13.將一些HTML元素轉換爲實體：

$naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss';
$str = preg_replace_callback('#<(/*\s*)('.$naughty.')([^><]*)([><]*)#is', array($this, '_sanitize_naughty_html'), $str);

14.清除一些腳本元素：

$str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', "\\1\\2(\\3)", $str);

15.最後的過濾：

$str = $this->_do_never_allowed($str);

最後返回$str

ximengyun

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