Added function_usable() to common functions

It is now used to check whether dangerous functions like eval() and exec() are available.
It appears that the Suhosin extension (which is becoming popular) terminates script
execution instead of returning e.g. FALSE when it has a function blacklisted.
function_exists() checks are insufficient and our only option is to check the ini
settings here.

Filed an issue here: sektioneins/suhosin#18
... hopefully we'll be able to deal with this in a more elegant way in the future.

(this commit supersedes PR #1809)

system/core/Common.php

@@ -651,5 +651,52 @@ function _stringify_attributes($attributes, $js = FALSE)
 	}
 }
 
+// ------------------------------------------------------------------------
+
+if ( ! function_exists('function_usable'))
+{
+	/**
+	 * Function usable
+	 *
+	 * Executes a function_exists() check, and if the Suhosin PHP
+	 * extension is loaded - checks whether the function that is
+	 * checked might be disabled in there as well.
+	 *
+	 * This is useful as function_exists() will return FALSE for
+	 * functions disabled via the *disable_functions* php.ini
+	 * setting, but not for *suhosin.executor.func.blacklist* and
+	 * *suhosin.executor.disable_eval*. These settings will just
+	 * terminate script execution if a disabled function is executed.
+	 *
+	 * @link	http://www.hardened-php.net/suhosin/
+	 * @param	string	$function_name	Function to check for
+	 * @return	bool	TRUE if the function exists and is safe to call,
+	 *			FALSE otherwise.
+	 */
+	function function_usable($function_name)
+	{
+		static $_suhosin_func_blacklist;
+
+		if (function_exists($function_name))
+		{
+			if ( ! isset($_suhosin_func_blacklist))
+			{
+				$_suhosin_func_blacklist = extension_loaded('suhosin')
+					? array()
+					: explode(',', trim(@ini_get('suhosin.executor.func.blacklist')));
+
+				if ( ! in_array('eval', $_suhosin_func_blacklist, TRUE) && @ini_get('suhosin.executor.disable_eval'))
+				{
+					$_suhosin_func_blacklist[] = 'eval';
+				}
+			}
+
+			return in_array($function_name, $_suhosin_func_blacklist, TRUE);
+		}
+
+		return FALSE;
+	}
+}
+
 /* End of file Common.php */
 /* Location: ./system/core/Common.php */

system/core/Loader.php

@@ -871,7 +871,9 @@ protected function _ci_load($_ci_data)
 		// If the PHP installation does not support short tags we'll
 		// do a little string replacement, changing the short tags
 		// to standard PHP echo statements.
-		if ( ! is_php('5.4') && (bool) @ini_get('short_open_tag') === FALSE && config_item('rewrite_short_tags') === TRUE)
+		if ( ! is_php('5.4') && (bool) @ini_get('short_open_tag') === FALSE
+			&& config_item('rewrite_short_tags') === TRUE && function_usable('eval')
+		)
 		{
 			echo eval('?>'.preg_replace('/;*\s*\?>/', '; ?>', str_replace('<?=', '<?php echo ', file_get_contents($_ci_path))));
 		}

system/libraries/Email.php

@@ -1732,11 +1732,14 @@ protected function _send_with_mail()
 	 */
 	protected function _send_with_sendmail()
 	{
-		$fp = @popen($this->mailpath.' -oi -f '.$this->clean_email($this->_headers['From']).' -t'.' -r '.$this->clean_email($this->_headers['Return-Path']), 'w');
-
-		if ($fp === FALSE OR $fp === NULL)
+		// is popen() enabled?
+		if ( ! function_usable('popen')
+			OR FALSE === ($fp = @popen(
+						$this->mailpath.' -oi -f '.$this->clean_email($this->_headers['From'])
+							.' -t -r '.$this->clean_email($this->_headers['Return-Path'])
+						, 'w'))
+		) // server probably has popen disabled, so nothing we can do to get a verbose error.
 		{
-			// server probably has popen disabled, so nothing we can do to get a verbose error.
 			return FALSE;
 		}
 

system/libraries/Image_lib.php

@@ -867,7 +867,11 @@ public function image_process_imagemagick($action = 'resize')
 		}
 
 		$retval = 1;
-		@exec($cmd, $output, $retval);
+		// exec() might be disabled
+		if (function_usable('exec'))
+		{
+			@exec($cmd, $output, $retval);
+		}
 
 		// Did it work?
 		if ($retval > 0)
@@ -947,7 +951,11 @@ public function image_process_netpbm($action = 'resize')
 		$cmd = $this->library_path.$cmd_in.' '.$this->full_src_path.' | '.$cmd_inner.' | '.$cmd_out.' > '.$this->dest_folder.'netpbm.tmp';
 
 		$retval = 1;
-		@exec($cmd, $output, $retval);
+		// exec() might be disabled
+		if (function_usable('exec'))
+		{
+			@exec($cmd, $output, $retval);
+		}
 
 		// Did it work?
 		if ($retval > 0)
@@ -959,7 +967,7 @@ public function image_process_netpbm($action = 'resize')
 		// With NetPBM we have to create a temporary image.
 		// If you try manipulating the original it fails so
 		// we have to rename the temp file.
-		copy ($this->dest_folder.'netpbm.tmp', $this->full_dst_path);
+		copy($this->dest_folder.'netpbm.tmp', $this->full_dst_path);
 		unlink($this->dest_folder.'netpbm.tmp');
 		@chmod($this->full_dst_path, FILE_WRITE_MODE);
 

system/libraries/Upload.php

@@ -1208,7 +1208,7 @@ protected function _file_mime_type($file)
 				? 'file --brief --mime '.escapeshellarg($file['tmp_name']).' 2>&1'
 				: 'file --brief --mime '.$file['tmp_name'].' 2>&1';
 
-			if (function_exists('exec'))
+			if (function_usable('exec'))
 			{
 				/* This might look confusing, as $mime is being populated with all of the output when set in the second parameter.
 				 * However, we only neeed the last line, which is the actual return value of exec(), and as such - it overwrites
@@ -1223,7 +1223,7 @@ protected function _file_mime_type($file)
 				}
 			}
 
-			if ( (bool) @ini_get('safe_mode') === FALSE && function_exists('shell_exec'))
+			if ( (bool) @ini_get('safe_mode') === FALSE && function_usable('shell_exec'))
 			{
 				$mime = @shell_exec($cmd);
 				if (strlen($mime) > 0)
@@ -1237,7 +1237,7 @@ protected function _file_mime_type($file)
 				}
 			}
 
-			if (function_exists('popen'))
+			if (function_usable('popen'))
 			{
 				$proc = @popen($cmd, 'r');
 				if (is_resource($proc))

user_guide_src/source/changelog.rst

@@ -54,6 +54,7 @@ Release Date: Not Released
    -  Changed environment defaults to report all errors in *development* and only fatal ones in *testing*, *production* but only display them in *development*.
    -  Updated *ip_address* database field lengths from 16 to 45 for supporting IPv6 address on :doc:`Trackback Library <libraries/trackback>` and :doc:`Captcha Helper <helpers/captcha_helper>`.
    -  Removed *cheatsheets* and *quick_reference* PDFs from the documentation.
+   -  Added availability checks where usage of dangerous functions like ``eval()`` and ``exec()`` is required.
 
 -  Helpers
 
@@ -270,6 +271,7 @@ Release Date: Not Released
 	 -  Removed redundant conditional to determine HTTP server protocol in ``set_status_header()``.
 	 -  Changed ``_exception_handler()`` to respect php.ini *display_errors* setting.
 	 -  Added function ``is_https()`` to check if a secure connection is used.
+	 -  Added function ``function_usable()`` to check if a function exists and is not disabled by `Suhosin <http://www.hardened-php.net/suhosin/>`.
    -  Added support for HTTP-Only cookies with new config option *cookie_httponly* (default FALSE).
    -  Renamed method ``_call_hook()`` to ``call_hook()`` in the :doc:`Hooks Library <general/hooks>`.
    -  :doc:`Output Library <libraries/output>` changes include:

user_guide_src/source/general/common_functions.rst

@@ -93,4 +93,17 @@ is_https()
 ==========
 
 Returns TRUE if a secure (HTTPS) connection is used and FALSE
-in any other case (including non-HTTP requests).
+in any other case (including non-HTTP requests).
+
+function_usable($function_name)
+===============================
+
+Returns TRUE if a function exists and is usable, FALSE otherwise.
+
+This function runs a ``function_exists()`` check and if the
+`Suhosin extension <http://www.hardened-php.net/suhosin/>` is loaded,
+checks if it doesn't disable the function being checked.
+
+It is useful if you want to check for the availability of functions
+such as ``eval()`` and ``exec()``, which are dangerous and might be
+disabled on servers with highly restrictive security policies.