NAME¶
Text::MicroMason::Safe - Compile all Templates in a Safe Compartment
SYNOPSIS¶
Instead of using this class directly, pass its name to be mixed in:
use Text::MicroMason;
my $mason = Text::MicroMason->new( -Safe );
Use the standard compile and execute methods to parse and evalute templates:
print $mason->compile( text=>$template )->( @%args );
print $mason->execute( text=>$template, @args );
Safe usage restricts templates from accessing your files or data:
print $mason->execute( text=>"<% qx! cat /etc/passwd ! %>" ); # dies
print $mason->execute( text=>"The time is <% time() %>." ); # dies
DESCRIPTION¶
This package adds support for Safe compartments to MicroMason, allowing you to
restrict the operations that a template can perform.
By default, these safe calls prevent the code in a template from performing any
system activity or accessing any of your other Perl code. Violations may
result in either compile-time or run-time errors, so make sure you are using
an eval block or the CatchErrors trait to catch exceptions.
use Text::MicroMason;
my $mason = Text::MicroMason->new( -Safe );
$result = eval { $mason->execute( text => $template ) };
Caution: Although this appears to provide a significant amount of
security for untrusted templates, please take this with a grain of salt. A bug
in either this module or in the core Safe module could allow a clever attacker
to defeat the protection. At least one bug in the Safe module has been found
and fixed in years past, and there could be others.
Supported Attributes¶
- safe
- Optional reference to a Safe compartment. If you do not provide this, one
is generated for you.
To enable some operations or share variables or functions with the template
code, create a Safe compartment and configure it before passing it in as
the value of the "safe" attribute:
$safe = Safe->new();
$safe->permit('time');
$safe->share('$foo');
$mason = Text::MicroMason->new( -Safe, safe => $safe );
$result = eval { $mason->execute( text => $template ) };
- safe_methods
- IMPORTANT NOTE: The "safe_methods" parameter is
deprecated and will be removed in future versions of Text::MicroMason
(unless a Safe and future-proof implementation can be found). If you use
this parameter, you will receive a warning via carp:
"* WARNING: safe_methods is deprecated; please see the pod"
This parameter works correctly with sufficiently old versions of the Safe
module (prior to the release of perl 5.12.1), but modern versions of Safe
make it impossible for a Safe compartment to run any code outside the
compartment. Even with the object shared within the Safe compartment,
there is currently no known way to call methods on it without defining the
whole class within the compartment (which isn't safe).
If anyone has an appropriately safe solution that will allow
"safe_methods" to work, please submit a patch to the module
maintainer. Also see t/32-safe.t for tests related to
"safe_methods" that are currently being skipped.
The following pod is provided for legacy purposes only. It is strongly
recommended that you do not use this method. It is no longer allowed to
call methods from within a "Safe" template, because it isn't
actually safe.
A space-separated string of methods names to be supported by the
Safe::Facade.
To control which Mason methods are available within the template, pass a
"safe_methods" argument to new() followed by the method
names in a space-separated string.
For example, to allow templates to include other templates, using
$m->execute or the "<& file &>" include syntax,
you would need to allow the execute method. We'll also load the
TemplateDir mixin with strict_root on to prevent inclusion of templates
from outside the current directory.
# safe_methods is DEPRECATED, please see above
$mason = Text::MicroMason->new( -Safe, safe_methods => 'execute',
-TemplateDir, strict_root => 1 );
If you're combining this with the Filters mixin, you'll also need to allow
calls to the filter method; to allow multiple methods, join their names
with spaces:
# safe_methods is DEPRECATED, please see above
$mason = Text::MicroMason->new( -Safe, safe_methods => 'execute filter',
-TemplateDir, strict_root => 1,
-Filters );
Private Methods¶
- eval_sub()
- Instead of the eval() used by the base class, this calls
reval() on a Safe compartment.
- safe_compartment()
- Returns the Safe compartment passed by the user or generates a new
one.
- safe_facade()
- Generates an instance of the Safe::Facade equipped with only the methods
listed in the safe_methods attribute.
Private Safe::Facade class¶
Code compiled in a Safe compartment only has access to a limited version of the
template compiler in the $m variable, and can not make changes to the
attributes of the real MicroMason object. This limited object is an instance
of the Text::MicroMason::Safe::Facade class and can only perform certain
pre-defined methods.
- new()
- Creates a new hash-based instance mapping method names to subroutine
references.
- facade_method()
- Calls a named method by looking up the corresponding subroutine and
calling it.
- AUTOLOAD()
- Generates wrapper methods that call the facade_method() for any
lowercase method name.
SEE ALSO¶
For an overview of this templating framework, see Text::MicroMason.
This is a mixin class intended for use with Text::MicroMason::Base.
For distribution, installation, support, copyright and license information, see
Text::MicroMason::Docs::ReadMe.