Untrusted environment

Untrusted environment is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Sometimes it is useful to run code with inputs from untrusted users, untrusted code, etc. Explain the features your language uses in these circumstances and give sample code.

The intention is that the definition is to be interpreted broadly; different languages will solve this task in very different ways and with (generally) incomparable results.

PARI/GP

GP has a default, secure, which disallows the system and extern commands. Once activated this default cannot be removed without input from the user (i.e., not a script).

<lang parigp>default(secure,1); system("del file.txt"); default(secure,0); \\ Ineffective without user input</lang>

Perl

Perl can be invoked in taint mode with the command line option -T. While in this mode input from the user, and all variables derived from it, cannot be used in certain contexts until 'sanitized' by being passed through a regular expression.

<lang perl>#!/usr/bin/perl -T my $f = $ARGV[0]; open FILE, ">$f" or die 'Cannot open file for writing'; print FILE "Modifying an arbitrary file\n"; close FILE;</lang>

Ruby

Ruby handles untrusted input with the global variable $SAFE. Settings higher than 0 invoke an increasing level of sandboxing and general paranoia. <lang ruby>require 'cgi' $SAFE = 4 cgi = CGI::new("html4") eval(cgi["arbitrary_input"].to_s)</lang>

UNIX Shell

Sometimes chroot jails are used to add a layer of security to <lang bash>mkdir ~/jail cd ~/jail; chroot ~/jail; setuid(9); # if 9 is the userid of a non-root user rm /etc/hosts # actually points to ~/jail/etc/hosts</lang>