eval() == evil? --- How to use it safely?

castironpi castironpi at gmail.com
Fri Aug 29 21:22:25 CEST 2008


On Aug 29, 1:51 pm, Fett <FettMan... at gmail.com> wrote:
> > Your way of thinking is similar to Microsoft's. Encrypting and Signing
> > is a kludge, a real fix should fix the underlying cause. Anyway using
> > data parsers isn't that much harder than using eval/exec.
>
> While I agree that in this situation I should do both, what would you
> propose for cases where the data being sent is supposed to be
> executable code:
>
> I happen to know that for enterprise disk drives (like what Google
> uses to store everything) the firmware is protected by exactly what I
> describe. Since the firmware has to be able to run, the kind of fix
> you propose is not possible. I would assume that if this kind of data
> transfer was deemed poor, that Google and others would be demanding
> something better (can you imagine if Google's database stopped working
> because someone overwrote the firmware on their hard-drive?).
>
> Again, I suppose that in this case writing a parser is a better option
> (parsing a dict with strings by hand is faster than reading
> documentation on someone else's parser anyway), but both is the best
> option by far.
>
> Again, thank you all for your help.

I as a fan of biological structures tend to favor the 'many-small'
strategy: expose your servers, but only a fraction to any given
source.  If one of them crashes, blacklist their recent sources.
Distribute and decentralize ("redundantfy").  Compare I guess to a jet
plane with 1,000 engines, of which a few can fail no problem.
Resources can be expendable in small proportions.

More generally, think of a minimalist operating system, that can
tolerate malicious code execution, and just crash and reboot a lot.
If 'foreign code' execution is fundamental to the project, you might
even look at custom hardware.  Otherwise, if it's a lower priority,
just run a custom Python install, and delete modules like os.py,
os.path.py, and maybe even sys.py.  Either remove their corresponding
libraries, or create a wrapper that gets Admin approval for calls like
'subprocess.exec' and 'os.path.remove'.

You notice Windows now obtains User approval for internet access by a
new program it doesn't recognize.



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