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: https://github.com/stefanesser/suhosin/issues/18
... hopefully we'll be able to deal with this in a more elegant way in the future.

(this commit supersedes PR #1809)

5 files changed, 71 insertions, 11 deletions

diff --git a/system/core/Common.php b/system/core/Common.php
index 3b7ea6ad4..aea5f1808 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -651,5 +651,52 @@ if ( ! function_exists('_stringify_attributes'))
 	}
 }
 
+// ------------------------------------------------------------------------
+
+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, $_suhosin_func_blacklist, TRUE);
+		}
+
+		return FALSE;
+	}
+}
+
 /* End of file Common.php */
 /* Location: ./system/core/Common.php */
\ No newline at end of file
diff --git a/system/core/Loader.php b/system/core/Loader.php
index 9525f35d0..a9eec396c 100644
--- a/system/core/Loader.php
+++ b/system/core/Loader.php
@@ -871,7 +871,9 @@ class CI_Loader {
 		// If the PHP installation does not support short tags we'll
 		// do a little string replacement, changing the short tags
 		// to standard PHP echo statements.
-		if ( ! is_php('5.4') && (bool) @ini_get('short_open_tag') === FALSE && config_item('rewrite_short_tags') === TRUE)
+		if ( ! is_php('5.4') && (bool) @ini_get('short_open_tag') === FALSE
+			&& config_item('rewrite_short_tags') === TRUE && function_usable('eval')
+		)
 		{
 			echo eval('?>'.preg_replace('/;*\s*\?>/', '; ?>', str_replace('<?=', '<?php echo ', file_get_contents($_ci_path))));
 		}
diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index f3718ae7e..d23be1af1 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1732,11 +1732,14 @@ class CI_Email {
 	 */
 	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;
 		}
 
diff --git a/system/libraries/Image_lib.php b/system/libraries/Image_lib.php
index 3b453be47..9379e3ec8 100644
--- a/system/libraries/Image_lib.php
+++ b/system/libraries/Image_lib.php
@@ -867,7 +867,11 @@ class CI_Image_lib {
 		}
 
 		$retval = 1;
-		@exec($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 @@ class CI_Image_lib {
 		$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 ($retval > 0)
@@ -959,7 +967,7 @@ class CI_Image_lib {
 		// With NetPBM we have to create a temporary image.
 		// If you try manipulating the original it fails so
 		// we have to rename the temp file.
-		copy ($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);
 
diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index 013644963..b3e9f7515 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -1208,7 +1208,7 @@ class CI_Upload {
 				? '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 @@ class CI_Upload {
 				}
 			}
 
-			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 @@ class CI_Upload {
 				}
 			}
 
-			if (function_exists('popen'))
+			if (function_usable('popen'))
 			{
 				$proc = @popen($cmd, 'r');
 				if (is_resource($proc))