[Openmcl-devel] modify lisp reader such that :: is disallowed

Taoufik Dachraoui taoufik.dachraoui at wanadoo.fr
Thu Jun 11 09:14:53 PDT 2009

On Jun 11, 2009, at 5:56 PM, Ron Garret wrote:

> On Jun 11, 2009, at 8:09 AM, Taoufik Dachraoui wrote:
>> Hi
>> Users will not have access to intern, find-package, ...
>> I implemented a loader that exports public symbols and shadow  
>> unwanted
>> symbols
>> so that users will not be able to use any private or shadowed  
>> symbols.
>> the only problem I am facing today (as far as I can see right now)  
>> is to
>> disallow users to access non exported symbols by using the double
>> colons (::)
> The "as far as I can see right now" is a very important disclaimer.   
> The main problem with security is that there's a very big gap  
> between appearing to be secure and actually being secure.  People  
> make careers out of bridging that gap, and still very often they get  
> it wrong.  Not that I really want to discourage you -- it's good  
> that you're being ambitious, but it's important that you understand  
> the magnitude of the problem you are attempting to solve.
>> I tried to use set-macro-character and set-dispatch-macro-character
>> but failed, and
>> the reason is that the lisp reader as soon as it finds a macro-
>> character the previously
>> read word will be considered as a token and there is no way to  
>> rollback.
> Why is that a problem?
> Is there a reason you don't just pre-process the string to remove  
> all colons before reading it?  Or simply reject any string  
> containing colons?
> rg

I thought about processing the string before passing it to the reader  
but I
think it is better to leave the lisp reader deal with it (faster); but  
it seems
that there is no solution at sight right now; probably only by modifying
(hacking) the ccl lisp reader.

Another way is to create a set-macro-character for #\: and throw an  
but this will inhibit the use of keywords.

About making lisp secure:

Suppose you have access to a limited set of symbols (known as secure),
and that the colons are forbidden, then how a user can access symbols
in packages that he did not inherit?

I think the question, is what are the lisp symbols that must be  
in a secure environment? streams, processes, eval, compile, ...

I just want to try hard before I abandon. I am looking forward to read
discussions about a secure lisp environment.

Kind regards


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