[ python-Bugs-666700 ] os.popen+() can take string list and bypass shell.

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Bugs item #666700, was opened at 2003-01-12 13:45
Message generated for change (Comment added) made by facundobatista
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Category: Documentation
>Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Dani (asqui)
Assigned to: Nobody/Anonymous (nobody)
Summary: os.popen+() can take string list and bypass shell.

Initial Comment:
After being somewhat dumbfounded by the fact that there
is no easy way to securely give user input as
parameters to an external utility (because of the fact
that os.popen*() runs things in the shell), I was happy
to find that (os | popen2).popen[234]() will accept
either a string as the command and execute it within a
shell, or a string list which is executed directly.

This does not apply to os.popen(), however
popen2.popen[234]() all use this piece of code to
execute the command in the child process:

/usr/lib/python2.2/popen2.py
    def _run_child(self, cmd):
        if isinstance(cmd, types.StringTypes):
            cmd = ['/bin/sh', '-c', cmd]
        for i in range(3, MAXFD):
            try:
                os.close(i)
            except:
                pass
        try:
            os.execvp(cmd[0], cmd)
        finally:
            os._exit(1)

Meaning that unless cmd is a string it will be run
directly, outside of any shell.

This appears to be the case for os.popen[234]() as well
as popen2.popen*()

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>Comment By: Facundo Batista (facundobatista)
Date: 2005-01-11 12:19

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Jeremy, could you please provide a patch for the docs? Thanks!

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Comment By: Jeremy Fincher (jemfinch)
Date: 2005-01-11 12:08

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Yes, I believe it should.

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Comment By: Facundo Batista (facundobatista)
Date: 2005-01-11 00:34

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Should this be fixed in 2.4? Now we have the "subprocess"
module.

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Comment By: Facundo Batista (facundobatista)
Date: 2005-01-11 00:34

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Please, could you verify if this problem persists in Python 2.3.4
or 2.4?

If yes, in which version? Can you provide a test case?

If the problem is solved, from which version?

Note that if you fail to answer in one month, I'll close this bug
as "Won't fix".

Thank you! 

.    Facundo

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Comment By: Jeremy Fincher (jemfinch)
Date: 2003-09-23 19:34

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Can I second that the documentation should definitely be
updated to reflect this possibility, even if it's only
available on *nix-like systems?  This is something that many
other languages in the same realm as Python (Perl, PHP,
etc.) support and document, and I can't see any good reason
why we *shouldn't* document a more secure way to give data
to external programs.

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Comment By: Bernhard Herzog (bernhard)
Date: 2003-08-05 13:04

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Given that the command as list of strings feature only works
on Unix-like systems, ISTM it should perhaps only be
documented for the PopenN classes. Maybe the documentation
for the functions should state that on unix they accept
lists of strings, though.

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Comment By: Dani (asqui)
Date: 2003-01-12 13:49

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(The punch line which I omitted was that this fact is not
documented anywhere.)

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