"Perhaps I know more of these pursuers than you do. You fear them, but you do not fear them enough, yet."
Games::Golf does not have adequate safeguards against malicious code. The onus to prevent damage rests upon the user, as per the license.
Perl golfing entails scripts composed of obfuscated character sequences, known as "line noise". Good players pride themselves on keeping the Signal to Noise ratio as low as they can. Unfortunately, the consequence is that the distinction between safe and malicious code may be blurred.
Automated testing and submission ought only to be done if the module has been supplemented by a good security model. Some provision has been made for this, and shall be explained later in this document.
To assist with improving security, below we shall discuss risks and how to avoid them.
"We cannot count on getting anything to eat between here and Rivendell, except what we take with us, and we ought to take plenty to spare."
A secure multi-user operating system, such as BSD, Linux or a commercial Unix, is called for. The average Windows installation leans unrealistically towards a utopia world, one without the menace of crackers, viruses, worms, Trojans et all. Unsurprisingly, we shall pay little attention to the Redmond giant's products within this discussion.
Ideally, the responsibility for management (e.g. PGAS) is physically running on a different machine from those running the golf scripts. An exemplar setup uses a star network configuration between the management system (server) and the test machines (clients). The author suggests that these systems could be purchased inexpensively from a computer fair or auction.
The systems used to execute the golf scripts should be unadorned with unnecessary features and program. If possible, the operating system kernel should be complied or configured to have as little as possible (e.g. omit SysV shared memory). Filesystems should also be mounted read only, or placed on a read-only medium such as CDR. See your operating system documentation and the Further reading section of this document for more information.
A set of directores is required by the test system and the scripts being tested. A suggested (relative) hierarchy is:
./cache/ - cache directory ./root/ - root filesystem for scripts being tested (includes perl and libs) ./suite/ - testsuites
TODO: Cut my Perl, and install into here - working out !!FIXME!! This is really README material.
The author suggests the hierarchy should be located in subdirectory off the root directory called "golf".
The typical perl installation comprises of "non-standard" modules, and Perl's platform dependant functions. By comparison, most competition rules specify that scripts must be pure Perl, platform independent and not requiring modules other than those distributed as standard with perl.
Our solution to this problem is to build a new version of perl, which is installed We must build a new perl to these restrictions we need to get our hands dirty, and rebuild perl
TODO: Information regarding how to build perl with things removed. In particular, say what should be removed and kept in - on the basis of what would be implemented on the two standard golfing platforms - Windows and Unix. Some other features such as networking should be suggested for omission since they generally are impractical for a golf competition. We should note that if used in an obfuscation competition many of these should be left in.
"...there are some folk in Bree who are not to be trusted."
The test suite for a particular hole is loaded via:
my $test = Games::Golf::TestSuite->new("hole");
where hole.t is a Perl script that implements the tests.
We have not used the Safe module, yet the script is evaluated via eval(). This means that hole can change package variables in any package it pleases.
Unless we use another scheme then you will need to ensure the safety of the hole script. Hence, make sure that it cannot be modified according to the file permissions of the script under test. We recommend that it is set to read only in the ownership of another user.
On the other hand, hole is the testsuite that is used for testing players entries. It is usually written by the referees. Which means that this file is dangerous if it was modified in transit, or if the organisers are themselves dangerous.
"We will all remain together and bar this window and the door."
> chroot environment
> user permissions (keep separate from the test script)
> create a user/group account for testing
"This is where we leave the open and take to cover"
> firewall to restrict all ports
>
"Hadn't we better clear out quick, Mr Strider?"
> deleting temporaries and unwanted files after each iteration
"I had to study _you_ first, and make sure of you. The Enemy has set traps for me before now."
www.linuxdoc.com - Security HOWTO www.linuxdoc.com - Securing RedHat Linux (Book)
To install Games::Golf, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Games::Golf
CPAN shell
perl -MCPAN -e shell install Games::Golf
For more information on module installation, please visit the detailed CPAN module installation guide.