[Tutor] exec, execfile, rexec

[DS]

Kent Johnson wrote:

>It is very challenging to even come close to safety. If you search 
>comp.lang.python for eval or exec you will find many discussions of 
>this. For example
>http://groups.google.com/group/comp.lang.python/browse_frm/thread/cf6093c5551a6587/23ddf23a6dfc3e11?q=eval&rnum=1#23ddf23a6dfc3e11
>
>One approach is to use the compiler module to parse the input data and 
>write a custom visitor for the parse tree that only allows 'safe' parse 
>elements to be processed. There is some discussion here:
>http://groups.google.com/group/comp.lang.python/browse_frm/thread/d5f4d7e2c397c2ca/5d1af7f9c7b1789b?q=python+compiler+safe+eval&rnum=1#5d1af7f9c7b1789b
>
>  
>
Thanks for the references.  I played with the parse tree yesterday a
little bit, for which I now have a little bit more understanding, since
I implemented my own extremely primitive version.  It had seemed like I
ought to be able to take advantage of it, if I had an adequate stop list.

>There is also a hack that provides an empty __builtin__ namespace to 
>eval which prevents at least naive attempts at hacking.
>
>Bottom line - it's a very hard problem which I don't think anyone has 
>solved to the satisfaction of all observers, though there are limited 
>solutions which some people find acceptable.
>
>  
>

Terry Carroll wrote:

>On Tue, 14 Feb 2006, Kent Johnson wrote:
>
>  
>
>>Bottom line - it's a very hard problem which I don't think anyone has 
>>solved to the satisfaction of all observers, though there are limited 
>>solutions which some people find acceptable.
>>    
>>
>
>I think it's telling that the restricted execution modules, rexex and
>Bastion, became disabled as of python 2.3; that gives an indication of how
>difficult a problem it is to fix.
>
>http://www.python.org/doc/lib/restricted.html
>
>  
>
I hate to admit it, but there are times when fear should be listened to,
and I think this is one of them.  So, I guess I'll move on to parsing it
myself.  Seems a shame though.

ds