I've just finished making this patch for my own use (diffed against
5.3 CVS):
http://darkrainfall.org/php-5.3-shellbypass.patch
In short, what it does is make proc_open()'s shell_bypass option
available to UNIX systems. This is accomplished by allowing the
"command" parameter to proc_open() to be an array of arguments to pass
to execv[e](). I've included a few tests to check the functionality.
(A few more tests could be devised to, for example, check that the
correct warning is issued if you pass an array without bypass_shell
set, or a string with it set, etc.)
The exact behavior of the argument array is:
1) The array must contain at least one element, at index 0.
2) The element at index 0 is always the exact command path passed to
execv[e]() (after being filtered through any safe_mode restrictions,
as with the normal behavior of proc_open()).
3) Any other elements form the argv array passed to execv[e](). By
convention the first of these arguments (argv[0] in the child process)
is the same as the command path, however my patch does NOT enforce or
assume this; it simply calls execv[e]($argument_array[0],
array_slice($argument_array, 1)).
This patch currently provides the only useful way to fork a process
without running a shell (pcntl_fork() + pcntl_exec() are useless since
there's no pcntl_dup2() to control the descriptors of the child).
Why would you want to avoid the shell?
- Efficiency. The shell is an extra, often unnecessary process, which
must parse the commandline given to it into individual arguments
according to all its various rules. Not to mention the overhead of
setting up another entire process just to run a third process.
- Resource control. The shell is an extra process. If you don't need
it, and your system is tight on process space, best to avoid it.
- Sanity. Correctly quoting arguments to a shell command ranges from
mildly annoying (escapeshellarg() in simple cases) to nightmarish
(manual parsing of a string in some edge cases). Passing arguments
directly completely bypasses this, quite possibly saving you quite a
bit of string parsing time if you were doing something like
"$shell_args = implode(' ', array_map('escapeshellarg', $raw_args));".
- Oddly enough, security. Since there's no shell, it's more difficult
to subvert the child process to do other things than the coder
intended (unless of course, said coder executes a shell this way).
This patch does nothing on Windows, since the option was already
implemented there. It also does nothing on Netware, since from what I
could see in the code, Netware doesn't have a shell in the first place.
I'm proposing the inclusion of this patch in HEAD (which I'll port it
to if I get a thumbs-up here), and possibly 5.3.2. Criticism and angry
flames welcome. Constructive critcism and good-natured comments will
be ignored ;) (just kidding... or am I?).
-- Gwynne
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