Is there a way to limit the functionality of eval?

_________
broquaint

Thank you for the suggestion.

I will look into Safe compartments to see how they work.

Richard

Here's an example of how to do that:

use Safe ;

  my $PACK = new Safe ;

  $PACK->deny(qw(
wantarray vec warn 
grepstart grepwhile mapstart mapwhile enteriter iter enterloop leavelo
+op unstack
last next redo goto
readline rcatline getc read formline enterwrite leavewrite
print sysread syswrite send recv
eof tell seek sysseek readdir telldir seekdir rewinddir
bless sprintf prtf crypt
tie untie dbmopen dbmclose
sselect select pipe_op sockpair
getppid getpgrp setpgrp getpriority setpriority localtime gmtime
rand srand atan2 sin cos exp log sqrt reset
chroot syscall dump exit die warn fork lock threadsv
  )) ;
  
  ## I use select to turn of output:
  my $sel = select(NULL) ;
  
  $PACK->reval(q`
  ## your code that need to be safe....
  `) ;
  
  ## select again the previous output:
  select($sel) ;
[download]

Graciliano M. P.
"The creativity is the expression of the liberty".

As others have noted in this thread, common security usage of a filtering tool is to permit only that which is known good and deeny all else, e.g.:

use Safe ;

my $PACK = new Safe ;

$PACK->permit_only( # good ops here
[download]

Bob Niederman, http://bob-n.com

Should work :)

--nutshell

With all due respect, every time you come up with something to remove, I and others can come up with something bad to put in there. For example, how would you "sanitize" the following (given the caveat that I didn't make it dangerous):

$_ = 'sub _{local $_=shift;y/A-Z/a-z/;y/0-9//d;$_}$_=q{P1R2I3N4T "R0M 
+-F0R"};s/(.*)/_($1)/sexe';
eval;
[download]

Cheers,
Ovid

New address of my CGI Course.
Silence is Evil (feel free to copy and distribute widely - note copyright text)

Generally speaking, the opposite approach is the way to go for most security situations. Disallow everything and only open what you want.

So if you have a handful of commands you're willing to eval, you could regex verify them. But trying to build a stop-list of things not to eval is fraught with terror, as Ovid demonstrates above.

Thank you for your suggestion.

To do a good job using regex I think I would need to know the difference between unlink the function and $unlink the variable (it might happen!) So I would basically be building a Perl parser for the string and complaining if the parser encountered any in my list of illegal functions.

I don't think this is very difficult but is there another way of doing this that is more reliable?

Richard