ext/Opcode/Safe.pm

package Safe;

use 5.003_11;
use strict;

$Safe::VERSION = "2.11";

# *** Don't declare any lexicals above this point ***
#
# This function should return a closure which contains an eval that can't
# see any lexicals in scope (apart from __ExPr__ which is unavoidable)

sub lexless_anon_sub {
                 # $_[0] is package;
                 # $_[1] is strict flag;
    my $__ExPr__ = $_[2];   # must be a lexical to create the closure that
                            # can be used to pass the value into the safe
                            # world

    # Create anon sub ref in root of compartment.
    # Uses a closure (on $__ExPr__) to pass in the code to be executed.
    # (eval on one line to keep line numbers as expected by caller)
    eval sprintf
    'package %s; %s strict; sub { @_=(); eval q[my $__ExPr__;] . $__ExPr__; }',
                $_[0], $_[1] ? 'use' : 'no';
}

use Carp;
use Carp::Heavy;

use Opcode 1.01, qw(
    opset opset_to_ops opmask_add
    empty_opset full_opset invert_opset verify_opset
    opdesc opcodes opmask define_optag opset_to_hex
);

*ops_to_opset = \&opset;   # Temporary alias for old Penguins


my $default_root  = 0;
my $default_share = ['*_']; #, '*main::'];

sub new {
    my($class, $root, $mask) = @_;
    my $obj = {};
    bless $obj, $class;

    if (defined($root)) {
        croak "Can't use \"$root\" as root name"
            if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
        $obj->{Root}  = $root;
        $obj->{Erase} = 0;
    }
    else {
        $obj->{Root}  = "Safe::Root".$default_root++;
        $obj->{Erase} = 1;
    }

    # use permit/deny methods instead till interface issues resolved
    # XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...;
    croak "Mask parameter to new no longer supported" if defined $mask;
    $obj->permit_only(':default');

    # We must share $_ and @_ with the compartment or else ops such
    # as split, length and so on won't default to $_ properly, nor
    # will passing argument to subroutines work (via @_). In fact,
    # for reasons I don't completely understand, we need to share
    # the whole glob *_ rather than $_ and @_ separately, otherwise
    # @_ in non default packages within the compartment don't work.
    $obj->share_from('main', $default_share);
    Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04);
    return $obj;
}

sub DESTROY {
    my $obj = shift;
    $obj->erase('DESTROY') if $obj->{Erase};
}

sub erase {
    my ($obj, $action) = @_;
    my $pkg = $obj->root();
    my ($stem, $leaf);

    no strict 'refs';
    $pkg = "main::$pkg\::";     # expand to full symbol table name
    ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;

    # The 'my $foo' is needed! Without it you get an
    # 'Attempt to free unreferenced scalar' warning!
    my $stem_symtab = *{$stem}{HASH};

    #warn "erase($pkg) stem=$stem, leaf=$leaf";
    #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
        # ", join(', ', %$stem_symtab),"\n";

#    delete $stem_symtab->{$leaf};

    my $leaf_glob   = $stem_symtab->{$leaf};
    my $leaf_symtab = *{$leaf_glob}{HASH};
#    warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
    %$leaf_symtab = ();
    #delete $leaf_symtab->{'__ANON__'};
    #delete $leaf_symtab->{'foo'};
    #delete $leaf_symtab->{'main::'};
#    my $foo = undef ${"$stem\::"}{"$leaf\::"};

    if ($action and $action eq 'DESTROY') {
        delete $stem_symtab->{$leaf};
    } else {
        $obj->share_from('main', $default_share);
    }
    1;
}


sub reinit {
    my $obj= shift;
    $obj->erase;
    $obj->share_redo;
}

sub root {
    my $obj = shift;
    croak("Safe root method now read-only") if @_;
    return $obj->{Root};
}


sub mask {
    my $obj = shift;
    return $obj->{Mask} unless @_;
    $obj->deny_only(@_);
}

# v1 compatibility methods
sub trap   { shift->deny(@_)   }
sub untrap { shift->permit(@_) }

sub deny {
    my $obj = shift;
    $obj->{Mask} |= opset(@_);
}
sub deny_only {
    my $obj = shift;
    $obj->{Mask} = opset(@_);
}

sub permit {
    my $obj = shift;
    # XXX needs testing
    $obj->{Mask} &= invert_opset opset(@_);
}
sub permit_only {
    my $obj = shift;
    $obj->{Mask} = invert_opset opset(@_);
}


sub dump_mask {
    my $obj = shift;
    print opset_to_hex($obj->{Mask}),"\n";
}


sub share {
    my($obj, @vars) = @_;
    $obj->share_from(scalar(caller), \@vars);
}

sub share_from {
    my $obj = shift;
    my $pkg = shift;
    my $vars = shift;
    my $no_record = shift || 0;
    my $root = $obj->root();
    croak("vars not an array ref") unless ref $vars eq 'ARRAY';
    no strict 'refs';
    # Check that 'from' package actually exists
    croak("Package \"$pkg\" does not exist")
        unless keys %{"$pkg\::"};
    my $arg;
    foreach $arg (@$vars) {
        # catch some $safe->share($var) errors:
        croak("'$arg' not a valid symbol table name")
            unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/
                or $arg =~ /^\$\W$/;
        my ($var, $type);
        $type = $1 if ($var = $arg) =~ s/^(\W)//;
        # warn "share_from $pkg $type $var";
        *{$root."::$var"} = (!$type)       ? \&{$pkg."::$var"}
                          : ($type eq '&') ? \&{$pkg."::$var"}
                          : ($type eq '$') ? \${$pkg."::$var"}
                          : ($type eq '@') ? \@{$pkg."::$var"}
                          : ($type eq '%') ? \%{$pkg."::$var"}
                          : ($type eq '*') ?  *{$pkg."::$var"}
                          : croak(qq(Can't share "$type$var" of unknown type));
    }
    $obj->share_record($pkg, $vars) unless $no_record or !$vars;
}

sub share_record {
    my $obj = shift;
    my $pkg = shift;
    my $vars = shift;
    my $shares = \%{$obj->{Shares} ||= {}};
    # Record shares using keys of $obj->{Shares}. See reinit.
    @{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
}
sub share_redo {
    my $obj = shift;
    my $shares = \%{$obj->{Shares} ||= {}};
    my($var, $pkg);
    while(($var, $pkg) = each %$shares) {
        # warn "share_redo $pkg\:: $var";
        $obj->share_from($pkg,  [ $var ], 1);
    }
}
sub share_forget {
    delete shift->{Shares};
}

sub varglob {
    my ($obj, $var) = @_;
    no strict 'refs';
    return *{$obj->root()."::$var"};
}


sub reval {
    my ($obj, $expr, $strict) = @_;
    my $root = $obj->{Root};

    my $evalsub = lexless_anon_sub($root,$strict, $expr);
    return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
}

sub rdo {
    my ($obj, $file) = @_;
    my $root = $obj->{Root};

    my $evalsub = eval
            sprintf('package %s; sub { @_ = (); do $file }', $root);
    return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
}


1;

__END__

=head1 NAME

Safe - Compile and execute code in restricted compartments

=head1 SYNOPSIS

  use Safe;

  $compartment = new Safe;

  $compartment->permit(qw(time sort :browse));

  $result = $compartment->reval($unsafe_code);

=head1 DESCRIPTION

The Safe extension module allows the creation of compartments
in which perl code can be evaluated. Each compartment has

=over 8

=item a new namespace

The "root" of the namespace (i.e. "main::") is changed to a
different package and code evaluated in the compartment cannot
refer to variables outside this namespace, even with run-time
glob lookups and other tricks.

Code which is compiled outside the compartment can choose to place
variables into (or I<share> variables with) the compartment's namespace
and only that data will be visible to code evaluated in the
compartment.

By default, the only variables shared with compartments are the
"underscore" variables $_ and @_ (and, technically, the less frequently
used %_, the _ filehandle and so on). This is because otherwise perl
operators which default to $_ will not work and neither will the
assignment of arguments to @_ on subroutine entry.

=item an operator mask

Each compartment has an associated "operator mask". Recall that
perl code is compiled into an internal format before execution.
Evaluating perl code (e.g. via "eval" or "do 'file'") causes
the code to be compiled into an internal format and then,
provided there was no error in the compilation, executed.
Code evaluated in a compartment compiles subject to the
compartment's operator mask. Attempting to evaluate code in a
compartment which contains a masked operator will cause the
compilation to fail with an error. The code will not be executed.

The default operator mask for a newly created compartment is
the ':default' optag.

It is important that you read the Opcode(3) module documentation
for more information, especially for detailed definitions of opnames,
optags and opsets.

Since it is only at the compilation stage that the operator mask
applies, controlled access to potentially unsafe operations can
be achieved by having a handle to a wrapper subroutine (written
outside the compartment) placed into the compartment. For example,

    $cpt = new Safe;
    sub wrapper {
        # vet arguments and perform potentially unsafe operations
    }
    $cpt->share('&wrapper');

=back


=head1 WARNING

The authors make B<no warranty>, implied or otherwise, about the
suitability of this software for safety or security purposes.

The authors shall not in any case be liable for special, incidental,
consequential, indirect or other similar damages arising from the use
of this software.

Your mileage will vary. If in any doubt B<do not use it>.


=head2 RECENT CHANGES

The interface to the Safe module has changed quite dramatically since
version 1 (as supplied with Perl5.002). Study these pages carefully if
you have code written to use Safe version 1 because you will need to
makes changes.


=head2 Methods in class Safe

To create a new compartment, use

    $cpt = new Safe;

Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
to use for the compartment (defaults to "Safe::Root0", incremented for
each new compartment).

Note that version 1.00 of the Safe module supported a second optional
parameter, MASK.  That functionality has been withdrawn pending deeper
consideration. Use the permit and deny methods described below.

The following methods can then be used on the compartment
object returned by the above constructor. The object argument
is implicit in each case.


=over 8

=item permit (OP, ...)

Permit the listed operators to be used when compiling code in the
compartment (in I<addition> to any operators already permitted).

=item permit_only (OP, ...)

Permit I<only> the listed operators to be used when compiling code in
the compartment (I<no> other operators are permitted).

=item deny (OP, ...)

Deny the listed operators from being used when compiling code in the
compartment (other operators may still be permitted).

=item deny_only (OP, ...)

Deny I<only> the listed operators from being used when compiling code
in the compartment (I<all> other operators will be permitted).

=item trap (OP, ...)

=item untrap (OP, ...)

The trap and untrap methods are synonyms for deny and permit
respectfully.

=item share (NAME, ...)

This shares the variable(s) in the argument list with the compartment.
This is almost identical to exporting variables using the L<Exporter>
module.

Each NAME must be the B<name> of a non-lexical variable, typically
with the leading type identifier included. A bareword is treated as a
function name.

Examples of legal names are '$foo' for a scalar, '@foo' for an
array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
for a glob (i.e.  all symbol table entries associated with "foo",
including scalar, array, hash, sub and filehandle).

Each NAME is assumed to be in the calling package. See share_from
for an alternative method (which share uses).

=item share_from (PACKAGE, ARRAYREF)

This method is similar to share() but allows you to explicitly name the
package that symbols should be shared from. The symbol names (including
type characters) are supplied as an array reference.

    $safe->share_from('main', [ '$foo', '%bar', 'func' ]);


=item varglob (VARNAME)

This returns a glob reference for the symbol table entry of VARNAME in
the package of the compartment. VARNAME must be the B<name> of a
variable without any leading type marker. For example,

    $cpt = new Safe 'Root';
    $Root::foo = "Hello world";
    # Equivalent version which doesn't need to know $cpt's package name:
    ${$cpt->varglob('foo')} = "Hello world";


=item reval (STRING)

This evaluates STRING as perl code inside the compartment.

The code can only see the compartment's namespace (as returned by the
B<root> method). The compartment's root package appears to be the
C<main::> package to the code inside the compartment.

Any attempt by the code in STRING to use an operator which is not permitted
by the compartment will cause an error (at run-time of the main program
but at compile-time for the code in STRING).  The error is of the form
"'%s' trapped by operation mask...".

If an operation is trapped in this way, then the code in STRING will
not be executed. If such a trapped operation occurs or any other
compile-time or return error, then $@ is set to the error message, just
as with an eval().

If there is no error, then the method returns the value of the last
expression evaluated, or a return statement may be used, just as with
subroutines and B<eval()>. The context (list or scalar) is determined
by the caller as usual.

This behaviour differs from the beta distribution of the Safe extension
where earlier versions of perl made it hard to mimic the return
behaviour of the eval() command and the context was always scalar.

Some points to note:

If the entereval op is permitted then the code can use eval "..." to
'hide' code which might use denied ops. This is not a major problem
since when the code tries to execute the eval it will fail because the
opmask is still in effect. However this technique would allow clever,
and possibly harmful, code to 'probe' the boundaries of what is
possible.

Any string eval which is executed by code executing in a compartment,
or by code called from code executing in a compartment, will be eval'd
in the namespace of the compartment. This is potentially a serious
problem.

Consider a function foo() in package pkg compiled outside a compartment
but shared with it. Assume the compartment has a root package called
'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
normally, $pkg::foo will be set to 1.  If foo() is called from the
compartment (by whatever means) then instead of setting $pkg::foo, the
eval will actually set $Root::pkg::foo.

This can easily be demonstrated by using a module, such as the Socket
module, which uses eval "..." as part of an AUTOLOAD function. You can
'use' the module outside the compartment and share an (autoloaded)
function with the compartment. If an autoload is triggered by code in
the compartment, or by any code anywhere that is called by any means
from the compartment, then the eval in the Socket module's AUTOLOAD
function happens in the namespace of the compartment. Any variables
created or used by the eval'd code are now under the control of
the code in the compartment.

A similar effect applies to I<all> runtime symbol lookups in code
called from a compartment but not compiled within it.


=item rdo (FILENAME)

This evaluates the contents of file FILENAME inside the compartment.
See above documentation on the B<reval> method for further details.

=item root (NAMESPACE)

This method returns the name of the package that is the root of the
compartment's namespace.

Note that this behaviour differs from version 1.00 of the Safe module
where the root module could be used to change the namespace. That
functionality has been withdrawn pending deeper consideration.

=item mask (MASK)

This is a get-or-set method for the compartment's operator mask.

With no MASK argument present, it returns the current operator mask of
the compartment.

With the MASK argument present, it sets the operator mask for the
compartment (equivalent to calling the deny_only method).

=back


=head2 Some Safety Issues

This section is currently just an outline of some of the things code in
a compartment might do (intentionally or unintentionally) which can
have an effect outside the compartment.

=over 8

=item Memory

Consuming all (or nearly all) available memory.

=item CPU

Causing infinite loops etc.

=item Snooping

Copying private information out of your system. Even something as
simple as your user name is of value to others. Much useful information
could be gleaned from your environment variables for example.

=item Signals

Causing signals (especially SIGFPE and SIGALARM) to affect your process.

Setting up a signal handler will need to be carefully considered
and controlled.  What mask is in effect when a signal handler
gets called?  If a user can get an imported function to get an
exception and call the user's signal handler, does that user's
restricted mask get re-instated before the handler is called?
Does an imported handler get called with its original mask or
the user's one?

=item State Changes

Ops such as chdir obviously effect the process as a whole and not just
the code in the compartment. Ops such as rand and srand have a similar
but more subtle effect.

=back

=head2 AUTHOR

Originally designed and implemented by Malcolm Beattie,
mbeattie@sable.ox.ac.uk.

Reworked to use the Opcode module and other changes added by Tim Bunce
E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.

=cut

Revision:	1.1
Committed:	Thu Jun 30 14:27:04 2005 UTC (21 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package Safe;
2
3			use 5.003_11;
4			use strict;
5
6			$Safe::VERSION = "2.11";
7
8			# * Don't declare any lexicals above this point *
9			#
10			# This function should return a closure which contains an eval that can't
11			# see any lexicals in scope (apart from __ExPr__ which is unavoidable)
12
13			sub lexless_anon_sub {
14			# $_[0] is package;
15			# $_[1] is strict flag;
16			my $__ExPr__ = $_[2]; # must be a lexical to create the closure that
17			# can be used to pass the value into the safe
18			# world
19
20			# Create anon sub ref in root of compartment.
21			# Uses a closure (on $__ExPr__) to pass in the code to be executed.
22			# (eval on one line to keep line numbers as expected by caller)
23			eval sprintf
24			'package %s; %s strict; sub { @_=(); eval q[my $__ExPr__;] . $__ExPr__; }',
25			$_[0], $_[1] ? 'use' : 'no';
26			}
27
28			use Carp;
29			use Carp::Heavy;
30
31			use Opcode 1.01, qw(
32			opset opset_to_ops opmask_add
33			empty_opset full_opset invert_opset verify_opset
34			opdesc opcodes opmask define_optag opset_to_hex
35			);
36
37			*ops_to_opset = \&opset; # Temporary alias for old Penguins
38
39
40			my $default_root = 0;
41			my $default_share = ['_']; #, 'main::'];
42
43			sub new {
44			my($class, $root, $mask) = @_;
45			my $obj = {};
46			bless $obj, $class;
47
48			if (defined($root)) {
49			croak "Can't use \"$root\" as root name"
50			if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
51			$obj->{Root} = $root;
52			$obj->{Erase} = 0;
53			}
54			else {
55			$obj->{Root} = "Safe::Root".$default_root++;
56			$obj->{Erase} = 1;
57			}
58
59			# use permit/deny methods instead till interface issues resolved
60			# XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...;
61			croak "Mask parameter to new no longer supported" if defined $mask;
62			$obj->permit_only(':default');
63
64			# We must share $_ and @_ with the compartment or else ops such
65			# as split, length and so on won't default to $_ properly, nor
66			# will passing argument to subroutines work (via @_). In fact,
67			# for reasons I don't completely understand, we need to share
68			# the whole glob *_ rather than $_ and @_ separately, otherwise
69			# @_ in non default packages within the compartment don't work.
70			$obj->share_from('main', $default_share);
71			Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04);
72			return $obj;
73			}
74
75			sub DESTROY {
76			my $obj = shift;
77			$obj->erase('DESTROY') if $obj->{Erase};
78			}
79
80			sub erase {
81			my ($obj, $action) = @_;
82			my $pkg = $obj->root();
83			my ($stem, $leaf);
84
85			no strict 'refs';
86			$pkg = "main::$pkg\::"; # expand to full symbol table name
87			($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
88
89			# The 'my $foo' is needed! Without it you get an
90			# 'Attempt to free unreferenced scalar' warning!
91			my $stem_symtab = *{$stem}{HASH};
92
93			#warn "erase($pkg) stem=$stem, leaf=$leaf";
94			#warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
95			# ", join(', ', %$stem_symtab),"\n";
96
97			# delete $stem_symtab->{$leaf};
98
99			my $leaf_glob = $stem_symtab->{$leaf};
100			my $leaf_symtab = *{$leaf_glob}{HASH};
101			# warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
102			%$leaf_symtab = ();
103			#delete $leaf_symtab->{'__ANON__'};
104			#delete $leaf_symtab->{'foo'};
105			#delete $leaf_symtab->{'main::'};
106			# my $foo = undef ${"$stem\::"}{"$leaf\::"};
107
108			if ($action and $action eq 'DESTROY') {
109			delete $stem_symtab->{$leaf};
110			} else {
111			$obj->share_from('main', $default_share);
112			}
113			1;
114			}
115
116
117			sub reinit {
118			my $obj= shift;
119			$obj->erase;
120			$obj->share_redo;
121			}
122
123			sub root {
124			my $obj = shift;
125			croak("Safe root method now read-only") if @_;
126			return $obj->{Root};
127			}
128
129
130			sub mask {
131			my $obj = shift;
132			return $obj->{Mask} unless @_;
133			$obj->deny_only(@_);
134			}
135
136			# v1 compatibility methods
137			sub trap { shift->deny(@_) }
138			sub untrap { shift->permit(@_) }
139
140			sub deny {
141			my $obj = shift;
142			$obj->{Mask} \|= opset(@_);
143			}
144			sub deny_only {
145			my $obj = shift;
146			$obj->{Mask} = opset(@_);
147			}
148
149			sub permit {
150			my $obj = shift;
151			# XXX needs testing
152			$obj->{Mask} &= invert_opset opset(@_);
153			}
154			sub permit_only {
155			my $obj = shift;
156			$obj->{Mask} = invert_opset opset(@_);
157			}
158
159
160			sub dump_mask {
161			my $obj = shift;
162			print opset_to_hex($obj->{Mask}),"\n";
163			}
164
165
166
167			sub share {
168			my($obj, @vars) = @_;
169			$obj->share_from(scalar(caller), \@vars);
170			}
171
172			sub share_from {
173			my $obj = shift;
174			my $pkg = shift;
175			my $vars = shift;
176			my $no_record = shift \|\| 0;
177			my $root = $obj->root();
178			croak("vars not an array ref") unless ref $vars eq 'ARRAY';
179			no strict 'refs';
180			# Check that 'from' package actually exists
181			croak("Package \"$pkg\" does not exist")
182			unless keys %{"$pkg\::"};
183			my $arg;
184			foreach $arg (@$vars) {
185			# catch some $safe->share($var) errors:
186			croak("'$arg' not a valid symbol table name")
187			unless $arg =~ /^[\$\@%&]?\w[\w:]$/
188			or $arg =~ /^\$\W$/;
189			my ($var, $type);
190			$type = $1 if ($var = $arg) =~ s/^(\W)//;
191			# warn "share_from $pkg $type $var";
192			*{$root."::$var"} = (!$type) ? \&{$pkg."::$var"}
193			: ($type eq '&') ? \&{$pkg."::$var"}
194			: ($type eq '$') ? \${$pkg."::$var"}
195			: ($type eq '@') ? \@{$pkg."::$var"}
196			: ($type eq '%') ? \%{$pkg."::$var"}
197			: ($type eq '') ? {$pkg."::$var"}
198			: croak(qq(Can't share "$type$var" of unknown type));
199			}
200			$obj->share_record($pkg, $vars) unless $no_record or !$vars;
201			}
202
203			sub share_record {
204			my $obj = shift;
205			my $pkg = shift;
206			my $vars = shift;
207			my $shares = \%{$obj->{Shares} \|\|= {}};
208			# Record shares using keys of $obj->{Shares}. See reinit.
209			@{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
210			}
211			sub share_redo {
212			my $obj = shift;
213			my $shares = \%{$obj->{Shares} \|\|= {}};
214			my($var, $pkg);
215			while(($var, $pkg) = each %$shares) {
216			# warn "share_redo $pkg\:: $var";
217			$obj->share_from($pkg, [ $var ], 1);
218			}
219			}
220			sub share_forget {
221			delete shift->{Shares};
222			}
223
224			sub varglob {
225			my ($obj, $var) = @_;
226			no strict 'refs';
227			return *{$obj->root()."::$var"};
228			}
229
230
231			sub reval {
232			my ($obj, $expr, $strict) = @_;
233			my $root = $obj->{Root};
234
235			my $evalsub = lexless_anon_sub($root,$strict, $expr);
236			return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
237			}
238
239			sub rdo {
240			my ($obj, $file) = @_;
241			my $root = $obj->{Root};
242
243			my $evalsub = eval
244			sprintf('package %s; sub { @_ = (); do $file }', $root);
245			return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
246			}
247
248
249			1;
250
251			__END__
252
253			=head1 NAME
254
255			Safe - Compile and execute code in restricted compartments
256
257			=head1 SYNOPSIS
258
259			use Safe;
260
261			$compartment = new Safe;
262
263			$compartment->permit(qw(time sort :browse));
264
265			$result = $compartment->reval($unsafe_code);
266
267			=head1 DESCRIPTION
268
269			The Safe extension module allows the creation of compartments
270			in which perl code can be evaluated. Each compartment has
271
272			=over 8
273
274			=item a new namespace
275
276			The "root" of the namespace (i.e. "main::") is changed to a
277			different package and code evaluated in the compartment cannot
278			refer to variables outside this namespace, even with run-time
279			glob lookups and other tricks.
280
281			Code which is compiled outside the compartment can choose to place
282			variables into (or I<share> variables with) the compartment's namespace
283			and only that data will be visible to code evaluated in the
284			compartment.
285
286			By default, the only variables shared with compartments are the
287			"underscore" variables $_ and @_ (and, technically, the less frequently
288			used %_, the _ filehandle and so on). This is because otherwise perl
289			operators which default to $_ will not work and neither will the
290			assignment of arguments to @_ on subroutine entry.
291
292			=item an operator mask
293
294			Each compartment has an associated "operator mask". Recall that
295			perl code is compiled into an internal format before execution.
296			Evaluating perl code (e.g. via "eval" or "do 'file'") causes
297			the code to be compiled into an internal format and then,
298			provided there was no error in the compilation, executed.
299			Code evaluated in a compartment compiles subject to the
300			compartment's operator mask. Attempting to evaluate code in a
301			compartment which contains a masked operator will cause the
302			compilation to fail with an error. The code will not be executed.
303
304			The default operator mask for a newly created compartment is
305			the ':default' optag.
306
307			It is important that you read the Opcode(3) module documentation
308			for more information, especially for detailed definitions of opnames,
309			optags and opsets.
310
311			Since it is only at the compilation stage that the operator mask
312			applies, controlled access to potentially unsafe operations can
313			be achieved by having a handle to a wrapper subroutine (written
314			outside the compartment) placed into the compartment. For example,
315
316			$cpt = new Safe;
317			sub wrapper {
318			# vet arguments and perform potentially unsafe operations
319			}
320			$cpt->share('&wrapper');
321
322			=back
323
324
325			=head1 WARNING
326
327			The authors make B<no warranty>, implied or otherwise, about the
328			suitability of this software for safety or security purposes.
329
330			The authors shall not in any case be liable for special, incidental,
331			consequential, indirect or other similar damages arising from the use
332			of this software.
333
334			Your mileage will vary. If in any doubt B<do not use it>.
335
336
337			=head2 RECENT CHANGES
338
339			The interface to the Safe module has changed quite dramatically since
340			version 1 (as supplied with Perl5.002). Study these pages carefully if
341			you have code written to use Safe version 1 because you will need to
342			makes changes.
343
344
345			=head2 Methods in class Safe
346
347			To create a new compartment, use
348
349			$cpt = new Safe;
350
351			Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
352			to use for the compartment (defaults to "Safe::Root0", incremented for
353			each new compartment).
354
355			Note that version 1.00 of the Safe module supported a second optional
356			parameter, MASK. That functionality has been withdrawn pending deeper
357			consideration. Use the permit and deny methods described below.
358
359			The following methods can then be used on the compartment
360			object returned by the above constructor. The object argument
361			is implicit in each case.
362
363
364			=over 8
365
366			=item permit (OP, ...)
367
368			Permit the listed operators to be used when compiling code in the
369			compartment (in I<addition> to any operators already permitted).
370
371			=item permit_only (OP, ...)
372
373			Permit I<only> the listed operators to be used when compiling code in
374			the compartment (I<no> other operators are permitted).
375
376			=item deny (OP, ...)
377
378			Deny the listed operators from being used when compiling code in the
379			compartment (other operators may still be permitted).
380
381			=item deny_only (OP, ...)
382
383			Deny I<only> the listed operators from being used when compiling code
384			in the compartment (I<all> other operators will be permitted).
385
386			=item trap (OP, ...)
387
388			=item untrap (OP, ...)
389
390			The trap and untrap methods are synonyms for deny and permit
391			respectfully.
392
393			=item share (NAME, ...)
394
395			This shares the variable(s) in the argument list with the compartment.
396			This is almost identical to exporting variables using the L<Exporter>
397			module.
398
399			Each NAME must be the B<name> of a non-lexical variable, typically
400			with the leading type identifier included. A bareword is treated as a
401			function name.
402
403			Examples of legal names are '$foo' for a scalar, '@foo' for an
404			array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
405			for a glob (i.e. all symbol table entries associated with "foo",
406			including scalar, array, hash, sub and filehandle).
407
408			Each NAME is assumed to be in the calling package. See share_from
409			for an alternative method (which share uses).
410
411			=item share_from (PACKAGE, ARRAYREF)
412
413			This method is similar to share() but allows you to explicitly name the
414			package that symbols should be shared from. The symbol names (including
415			type characters) are supplied as an array reference.
416
417			$safe->share_from('main', [ '$foo', '%bar', 'func' ]);
418
419
420			=item varglob (VARNAME)
421
422			This returns a glob reference for the symbol table entry of VARNAME in
423			the package of the compartment. VARNAME must be the B<name> of a
424			variable without any leading type marker. For example,
425
426			$cpt = new Safe 'Root';
427			$Root::foo = "Hello world";
428			# Equivalent version which doesn't need to know $cpt's package name:
429			${$cpt->varglob('foo')} = "Hello world";
430
431
432			=item reval (STRING)
433
434			This evaluates STRING as perl code inside the compartment.
435
436			The code can only see the compartment's namespace (as returned by the
437			B<root> method). The compartment's root package appears to be the
438			C<main::> package to the code inside the compartment.
439
440			Any attempt by the code in STRING to use an operator which is not permitted
441			by the compartment will cause an error (at run-time of the main program
442			but at compile-time for the code in STRING). The error is of the form
443			"'%s' trapped by operation mask...".
444
445			If an operation is trapped in this way, then the code in STRING will
446			not be executed. If such a trapped operation occurs or any other
447			compile-time or return error, then $@ is set to the error message, just
448			as with an eval().
449
450			If there is no error, then the method returns the value of the last
451			expression evaluated, or a return statement may be used, just as with
452			subroutines and B<eval()>. The context (list or scalar) is determined
453			by the caller as usual.
454
455			This behaviour differs from the beta distribution of the Safe extension
456			where earlier versions of perl made it hard to mimic the return
457			behaviour of the eval() command and the context was always scalar.
458
459			Some points to note:
460
461			If the entereval op is permitted then the code can use eval "..." to
462			'hide' code which might use denied ops. This is not a major problem
463			since when the code tries to execute the eval it will fail because the
464			opmask is still in effect. However this technique would allow clever,
465			and possibly harmful, code to 'probe' the boundaries of what is
466			possible.
467
468			Any string eval which is executed by code executing in a compartment,
469			or by code called from code executing in a compartment, will be eval'd
470			in the namespace of the compartment. This is potentially a serious
471			problem.
472
473			Consider a function foo() in package pkg compiled outside a compartment
474			but shared with it. Assume the compartment has a root package called
475			'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
476			normally, $pkg::foo will be set to 1. If foo() is called from the
477			compartment (by whatever means) then instead of setting $pkg::foo, the
478			eval will actually set $Root::pkg::foo.
479
480			This can easily be demonstrated by using a module, such as the Socket
481			module, which uses eval "..." as part of an AUTOLOAD function. You can
482			'use' the module outside the compartment and share an (autoloaded)
483			function with the compartment. If an autoload is triggered by code in
484			the compartment, or by any code anywhere that is called by any means
485			from the compartment, then the eval in the Socket module's AUTOLOAD
486			function happens in the namespace of the compartment. Any variables
487			created or used by the eval'd code are now under the control of
488			the code in the compartment.
489
490			A similar effect applies to I<all> runtime symbol lookups in code
491			called from a compartment but not compiled within it.
492
493
494
495			=item rdo (FILENAME)
496
497			This evaluates the contents of file FILENAME inside the compartment.
498			See above documentation on the B<reval> method for further details.
499
500			=item root (NAMESPACE)
501
502			This method returns the name of the package that is the root of the
503			compartment's namespace.
504
505			Note that this behaviour differs from version 1.00 of the Safe module
506			where the root module could be used to change the namespace. That
507			functionality has been withdrawn pending deeper consideration.
508
509			=item mask (MASK)
510
511			This is a get-or-set method for the compartment's operator mask.
512
513			With no MASK argument present, it returns the current operator mask of
514			the compartment.
515
516			With the MASK argument present, it sets the operator mask for the
517			compartment (equivalent to calling the deny_only method).
518
519			=back
520
521
522			=head2 Some Safety Issues
523
524			This section is currently just an outline of some of the things code in
525			a compartment might do (intentionally or unintentionally) which can
526			have an effect outside the compartment.
527
528			=over 8
529
530			=item Memory
531
532			Consuming all (or nearly all) available memory.
533
534			=item CPU
535
536			Causing infinite loops etc.
537
538			=item Snooping
539
540			Copying private information out of your system. Even something as
541			simple as your user name is of value to others. Much useful information
542			could be gleaned from your environment variables for example.
543
544			=item Signals
545
546			Causing signals (especially SIGFPE and SIGALARM) to affect your process.
547
548			Setting up a signal handler will need to be carefully considered
549			and controlled. What mask is in effect when a signal handler
550			gets called? If a user can get an imported function to get an
551			exception and call the user's signal handler, does that user's
552			restricted mask get re-instated before the handler is called?
553			Does an imported handler get called with its original mask or
554			the user's one?
555
556			=item State Changes
557
558			Ops such as chdir obviously effect the process as a whole and not just
559			the code in the compartment. Ops such as rand and srand have a similar
560			but more subtle effect.
561
562			=back
563
564			=head2 AUTHOR
565
566			Originally designed and implemented by Malcolm Beattie,
567			mbeattie@sable.ox.ac.uk.
568
569			Reworked to use the Opcode module and other changes added by Tim Bunce
570			E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.
571
572			=cut
573