Right, security implications are one of the reasons why I've held back from proposing Shell Command. The lack of cross platform support is also a pain. This suggestion shares both of those problems. Having dealt with long running child processes lately, I can also say that producing output line-by-line would be on my personal list of requirements. So, yeah, interesting idea, but this is still an area that needs a lot of exploration on PyPI before we select an answer for the stdlib. -- Sent from my phone, thus the relative brevity :)

On Wed, May 23, 2012 at 4:49 PM, Devin Jeanpierre wrote:

On Tue, May 22, 2012 at 5:41 PM, Nick Coghlan wrote:

...

Having dealt with long running child processes lately, I can also say that producing output line-by-line would be on my personal list of requirements.

You can do that with subprocess, right? Just have to be sure to close stdin/stderr and read p.stdout with readline() repeatedly...

Yep, subprocess is a swiss army knife - you can do pretty much anything with it. That's the complaint, though - *because* it's so configurable, even the existing convenience APIs aren't always that convenient for simple operations. Thus the current spate of efforts to provide a "friendlier" API for performing shell operations from Python. The dust may settle well enough in the 3.4 time frame for us to declare a "winner" and add something to the standard library, but that's far from certain. Cheers, Nick. -- Nick Coghlan   |   ncoghlan@gmail.com   |   Brisbane, Australia

About security. On Tue, May 22, 2012 at 11:30 PM, Mike Meyer wrote:

On Tue, 22 May 2012 18:39:16 +0300 anatoly techtonik wrote:

...

Therefore, inspired by Fabric API, I've finally found the solution - shutil.run() function: https://bitbucket.org/techtonik/shutil-run/src

run(command, combine_stderr=True):

    Run command through a system shell, return output string with     additional properties:

        output.succeeded    - result of the operation True/False         output.return_code  - specific return code         output.stderr       - stderr contents if combine_stderr=False

     `combine_stderr` if set, makes stderr merged into output string,      otherwise it will be available  as `output.stderr` attribute. [...] That's the most intuitive way I found so far. Objective advantages:

1. Better than        subprocess.call(cmd, shell=true)        subprocess.check_call(cmd, shell=true)        subprocess.check_output(cmd, shell=True)      because it is just        shutil.run(cmd)      i.e. short, simple and _easy to remember_

-2

Unless there's some way to turn off shell processing (better yet, have no shell processing be the default, and require that it be turned on), it can't be used securely with tainted strings, so it should *not* be used with tainted strings, which means it's pretty much useless in any environment where security matters. With everything being networked, there may no longer be any such environments.

What does this "shell processing" involve to understand what to turn off? Why there is no way to turn off "shell processing"? What's the primary reason that it is impossible to be turned off?

...

3. shutil.run() is predictable and consistent - its arguments are not dependent on each other, their combination doesn't change the function behavior over and over requiring you iterate over the documentation and warnings again and again

As proposed, it certainly provides a predictable and consistent vulnerability to code injection attacks.

suprocess.* with shell=True provides the same entrypoint for injection attacks, and security through obscurity doesn't help here. People still use shell=True, because that's sometimes the only way to execute external utilities properly. Even my synapses were silent when I reviewed and used shell=True for Rietveld upload script and Spyder IDE. What will help is a better simple explanation in a prominent place, with an example that people can really remember instead of frightening them with warnings. People will ignore warning eventually, and after endless experiments will subprocess.* params mess will just leave shell=True because it works (I did so). No sane web developer will use subprocess calls on server side at all. Regardless of shell=True or not. For example, how can I be sure that Graphviz is save from exploit through malicious input? No sane developer will run shell script on a web side either. For those who still want - there will be this simple explanation right on the shutil.run() page - with link to proper vulnerability analysis instead of uncertainty inducting warning. shutil.run() is aimed for local operations.

...

4. shutil.run() is the correct next level API over subprocess base level. subprocess executes external process - that is its role, but automatic ability to execute external process inside another external process (shell) looks like a hack to me. Practical, but still a hack.

It's only correct if you are in an environment where you don't care about security. If you care about security, you can't use it. If we're going to add yet another system() replacement, let's at least try and make it secure.

I am all ears how to make shutil.run() more secure. Right now I must confess that I don't even realize.how serious is this problems, so if anyone can came up with a real-world example with explanation of security concern that could be copied "as-is" into documentation, it will surely be appreciated not only by me.

On Wed, May 23, 2012 at 7:00 PM, Steven D'Aprano wrote:

anatoly techtonik wrote:

I am all ears how to make shutil.run() more secure. Right now I must

...

confess that I don't even realize.how serious is this problems, so if anyone can came up with a real-world example with explanation of security concern that could be copied "as-is" into documentation, it will surely be appreciated not only by me.

Start here:

http://cwe.mitre.org/top25/**index.htmlhttp://cwe.mitre.org/top25/index.html

Code injection attacks include two of the top three security vulnerabilities, over even buffer overflows.

One sub-category of code injection:

OS Command Injection http://cwe.mitre.org/data/**definitions/78.htmlhttp://cwe.mitre.org/data/definitions/78.html

I talked about this in my pycon talk this year. It's easy to avoid and disastrous to get wrong. Please don't do it this way. Geremy Condra

-- Steven

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On Mon, Jun 4, 2012 at 2:47 AM, anatoly techtonik wrote:

On Thu, May 24, 2012 at 6:24 AM, geremy condra wrote:

...

On Wed, May 23, 2012 at 7:00 PM, Steven D'Aprano wrote:

...

anatoly techtonik wrote:

...

I am all ears how to make shutil.run() more secure. Right now I must confess that I don't even realize.how serious is this problems, so if anyone can came up with a real-world example with explanation of security concern that could be copied "as-is" into documentation, it will surely be appreciated not only by me.

Start here:

http://cwe.mitre.org/top25/index.html

Code injection attacks include two of the top three security vulnerabilities, over even buffer overflows.

One sub-category of code injection:

OS Command Injection http://cwe.mitre.org/data/definitions/78.html

Great links. Thanks. Do they still too generic to be placed in docs?

...

I talked about this in my pycon talk this year. It's easy to avoid and disastrous to get wrong. Please don't do it this way.

Sorry, don't have too much time to watch it right now. Any specific slides, ideas or exceprts?

The main idea was just that by combining a bit of awareness of common security anti-patterns (like this one) with a good test regimen and some script kiddie tools you can protect yourself from a lot of common vulnerabilities without being a security guru. I demonstrated how that process works on something fairly similar to this, but if you're interested in more details I'm happy to blather on or dredge up my slides. Geremy Condra --

anatoly t.

On Mon, Jun 4, 2012 at 11:14 PM, Steven D'Aprano wrote:

On Mon, Jun 04, 2012 at 11:00:34PM -0700, geremy condra wrote:

...

The main idea was just that by combining a bit of awareness of common security anti-patterns (like this one) with a good test regimen and some script kiddie tools you can protect yourself from a lot of common vulnerabilities without being a security guru. I demonstrated how that process works on something fairly similar to this, but if you're interested in more details I'm happy to blather on or dredge up my slides.

I am interested in more details. Would this make a good How (Not) To for the documentation?

Combined with some other material I have on hand it might. Only problem would be that I don't really know my way around Sphinx- if there are any doc wizards on hand to help with formatting we could probably make a pretty quick job of it. Geremy Condra

-- Steven

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