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PORun executable from php without spawning a shell
 

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    <p>I need to call an executable from an imposed context of a PHP script. Both performance and security wise it's better not to call a shell at all between web server process and executable.</p> <p>Of course I searched the web, without success (in such a PHP context). Many other languages allow that and document it clearly.</p> <p>Alas, backticks, <code>exec()</code>, <code>shell_exec()</code>, <code>passthru()</code>, <code>system()</code>, <code>proc_open()</code>, <code>popen()</code> call a shell. And <code>pcntl_fork()</code> seems unavailable.</p> <h1>How to test if a function calls a shell or not.</h1> <p>This was tested on a Debian 6 64bit with PHP 5.3.3-7+squeeze15 . Test code on <a href="http://pastebin.com/y4C7MeJz" rel="noreferrer">http://pastebin.com/y4C7MeJz</a></p> <p>To get a meaningful test I used a trick which is to ask to execute a shell command not also available as an executable. A good example is <code>umask</code> . Any function returning something like 0022 definitely called a shell. <code>exec()</code>, <code>shell_exec()</code>, <code>passthru()</code>, <code>system()</code>, <code>proc_open()</code> all did. See detailed results on <a href="http://pastebin.com/RBcBz02F" rel="noreferrer">http://pastebin.com/RBcBz02F</a> .</p> <h1>pcntl_fork fails</h1> <p>Now, back the the goal : how to execute arbitrary program without launching a shell ?</p> <p>Php's exec takes as expected an array of string args instead of a unique string. But pcntl_fork just stops the requests without even a log.</p> <p>Edit: pcntl_fork failure is because the server uses Apache's mod_php, see <a href="http://www.php.net/manual/en/function.pcntl-fork.php#49949" rel="noreferrer">http://www.php.net/manual/en/function.pcntl-fork.php#49949</a> .</p> <p>Edit: added <code>popen()</code> to the tests, following @hakre suggestion.</p> <p>Any hint appreciated.</p>
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    1. COThe first time I found out that PHP does not seem to offer any mechanism to call an external program without passing a command line through a shell, I was alarmed and astonished. A general-purpose, popular, programming language that has commands like `exec()` and `system()` has this flaw and it's never been fixed? REALLY? But... I guess it's true.
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    2. CO@celada: you have to realize that PHP is just a wrapper around a large number of standard glib/libc functions. PHP itself cannot do anything that glib/libc don't do themselves, and one of those is executing another process via a shell.
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      1. USMarc B
    3. COWould PHP's umask not work? http://us2.php.net/umask
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      1. USMichael Duncan
 

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