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

Ron Garret ron at awun.net
Thu Jun 11 08:56:58 PDT 2009

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  


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