560 lines
16 KiB
Perl
560 lines
16 KiB
Perl
package Safe;
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use 5.003_11;
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use strict;
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use vars qw($VERSION);
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$VERSION = "2.06";
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use Carp;
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use Opcode 1.01, qw(
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opset opset_to_ops opmask_add
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empty_opset full_opset invert_opset verify_opset
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opdesc opcodes opmask define_optag opset_to_hex
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);
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*ops_to_opset = \&opset; # Temporary alias for old Penguins
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my $default_root = 0;
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my $default_share = ['*_']; #, '*main::'];
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sub new {
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my($class, $root, $mask) = @_;
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my $obj = {};
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bless $obj, $class;
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if (defined($root)) {
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croak "Can't use \"$root\" as root name"
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if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
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$obj->{Root} = $root;
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$obj->{Erase} = 0;
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}
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else {
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$obj->{Root} = "Safe::Root".$default_root++;
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$obj->{Erase} = 1;
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}
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# use permit/deny methods instead till interface issues resolved
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# XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...;
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croak "Mask parameter to new no longer supported" if defined $mask;
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$obj->permit_only(':default');
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# We must share $_ and @_ with the compartment or else ops such
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# as split, length and so on won't default to $_ properly, nor
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# will passing argument to subroutines work (via @_). In fact,
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# for reasons I don't completely understand, we need to share
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# the whole glob *_ rather than $_ and @_ separately, otherwise
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# @_ in non default packages within the compartment don't work.
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$obj->share_from('main', $default_share);
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return $obj;
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}
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sub DESTROY {
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my $obj = shift;
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$obj->erase('DESTROY') if $obj->{Erase};
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}
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sub erase {
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my ($obj, $action) = @_;
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my $pkg = $obj->root();
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my ($stem, $leaf);
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no strict 'refs';
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$pkg = "main::$pkg\::"; # expand to full symbol table name
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($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
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# The 'my $foo' is needed! Without it you get an
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# 'Attempt to free unreferenced scalar' warning!
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my $stem_symtab = *{$stem}{HASH};
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#warn "erase($pkg) stem=$stem, leaf=$leaf";
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#warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
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# ", join(', ', %$stem_symtab),"\n";
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# delete $stem_symtab->{$leaf};
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my $leaf_glob = $stem_symtab->{$leaf};
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my $leaf_symtab = *{$leaf_glob}{HASH};
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# warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
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%$leaf_symtab = ();
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#delete $leaf_symtab->{'__ANON__'};
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#delete $leaf_symtab->{'foo'};
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#delete $leaf_symtab->{'main::'};
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# my $foo = undef ${"$stem\::"}{"$leaf\::"};
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if ($action and $action eq 'DESTROY') {
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delete $stem_symtab->{$leaf};
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} else {
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$obj->share_from('main', $default_share);
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}
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1;
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}
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sub reinit {
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my $obj= shift;
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$obj->erase;
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$obj->share_redo;
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}
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sub root {
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my $obj = shift;
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croak("Safe root method now read-only") if @_;
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return $obj->{Root};
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}
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sub mask {
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my $obj = shift;
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return $obj->{Mask} unless @_;
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$obj->deny_only(@_);
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}
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# v1 compatibility methods
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sub trap { shift->deny(@_) }
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sub untrap { shift->permit(@_) }
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sub deny {
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my $obj = shift;
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$obj->{Mask} |= opset(@_);
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}
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sub deny_only {
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my $obj = shift;
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$obj->{Mask} = opset(@_);
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}
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sub permit {
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my $obj = shift;
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# XXX needs testing
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$obj->{Mask} &= invert_opset opset(@_);
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}
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sub permit_only {
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my $obj = shift;
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$obj->{Mask} = invert_opset opset(@_);
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}
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sub dump_mask {
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my $obj = shift;
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print opset_to_hex($obj->{Mask}),"\n";
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}
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sub share {
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my($obj, @vars) = @_;
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$obj->share_from(scalar(caller), \@vars);
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}
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sub share_from {
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my $obj = shift;
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my $pkg = shift;
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my $vars = shift;
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my $no_record = shift || 0;
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my $root = $obj->root();
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croak("vars not an array ref") unless ref $vars eq 'ARRAY';
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no strict 'refs';
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# Check that 'from' package actually exists
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croak("Package \"$pkg\" does not exist")
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unless keys %{"$pkg\::"};
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my $arg;
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foreach $arg (@$vars) {
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# catch some $safe->share($var) errors:
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croak("'$arg' not a valid symbol table name")
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unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/
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or $arg =~ /^\$\W$/;
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my ($var, $type);
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$type = $1 if ($var = $arg) =~ s/^(\W)//;
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# warn "share_from $pkg $type $var";
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*{$root."::$var"} = (!$type) ? \&{$pkg."::$var"}
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: ($type eq '&') ? \&{$pkg."::$var"}
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: ($type eq '$') ? \${$pkg."::$var"}
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: ($type eq '@') ? \@{$pkg."::$var"}
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: ($type eq '%') ? \%{$pkg."::$var"}
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: ($type eq '*') ? *{$pkg."::$var"}
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: croak(qq(Can't share "$type$var" of unknown type));
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}
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$obj->share_record($pkg, $vars) unless $no_record or !$vars;
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}
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sub share_record {
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my $obj = shift;
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my $pkg = shift;
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my $vars = shift;
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my $shares = \%{$obj->{Shares} ||= {}};
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# Record shares using keys of $obj->{Shares}. See reinit.
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@{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
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}
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sub share_redo {
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my $obj = shift;
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my $shares = \%{$obj->{Shares} ||= {}};
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my($var, $pkg);
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while(($var, $pkg) = each %$shares) {
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# warn "share_redo $pkg\:: $var";
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$obj->share_from($pkg, [ $var ], 1);
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}
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}
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sub share_forget {
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delete shift->{Shares};
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}
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sub varglob {
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my ($obj, $var) = @_;
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no strict 'refs';
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return *{$obj->root()."::$var"};
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}
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sub reval {
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my ($obj, $expr, $strict) = @_;
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my $root = $obj->{Root};
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# Create anon sub ref in root of compartment.
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# Uses a closure (on $expr) to pass in the code to be executed.
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# (eval on one line to keep line numbers as expected by caller)
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my $evalcode = sprintf('package %s; sub { eval $expr; }', $root);
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my $evalsub;
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if ($strict) { use strict; $evalsub = eval $evalcode; }
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else { no strict; $evalsub = eval $evalcode; }
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return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
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}
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sub rdo {
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my ($obj, $file) = @_;
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my $root = $obj->{Root};
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my $evalsub = eval
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sprintf('package %s; sub { do $file }', $root);
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return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
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}
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1;
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__DATA__
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=head1 NAME
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Safe - Compile and execute code in restricted compartments
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=head1 SYNOPSIS
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use Safe;
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$compartment = new Safe;
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$compartment->permit(qw(time sort :browse));
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$result = $compartment->reval($unsafe_code);
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=head1 DESCRIPTION
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The Safe extension module allows the creation of compartments
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in which perl code can be evaluated. Each compartment has
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=over 8
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=item a new namespace
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The "root" of the namespace (i.e. "main::") is changed to a
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different package and code evaluated in the compartment cannot
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refer to variables outside this namespace, even with run-time
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glob lookups and other tricks.
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Code which is compiled outside the compartment can choose to place
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variables into (or I<share> variables with) the compartment's namespace
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and only that data will be visible to code evaluated in the
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compartment.
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By default, the only variables shared with compartments are the
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"underscore" variables $_ and @_ (and, technically, the less frequently
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used %_, the _ filehandle and so on). This is because otherwise perl
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operators which default to $_ will not work and neither will the
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assignment of arguments to @_ on subroutine entry.
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=item an operator mask
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Each compartment has an associated "operator mask". Recall that
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perl code is compiled into an internal format before execution.
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Evaluating perl code (e.g. via "eval" or "do 'file'") causes
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the code to be compiled into an internal format and then,
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provided there was no error in the compilation, executed.
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Code evaluated in a compartment compiles subject to the
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compartment's operator mask. Attempting to evaluate code in a
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compartment which contains a masked operator will cause the
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compilation to fail with an error. The code will not be executed.
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The default operator mask for a newly created compartment is
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the ':default' optag.
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It is important that you read the Opcode(3) module documentation
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for more information, especially for detailed definitions of opnames,
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optags and opsets.
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Since it is only at the compilation stage that the operator mask
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applies, controlled access to potentially unsafe operations can
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be achieved by having a handle to a wrapper subroutine (written
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outside the compartment) placed into the compartment. For example,
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$cpt = new Safe;
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sub wrapper {
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# vet arguments and perform potentially unsafe operations
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}
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$cpt->share('&wrapper');
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=back
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=head1 WARNING
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The authors make B<no warranty>, implied or otherwise, about the
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suitability of this software for safety or security purposes.
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The authors shall not in any case be liable for special, incidental,
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consequential, indirect or other similar damages arising from the use
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of this software.
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Your mileage will vary. If in any doubt B<do not use it>.
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=head2 RECENT CHANGES
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The interface to the Safe module has changed quite dramatically since
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version 1 (as supplied with Perl5.002). Study these pages carefully if
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you have code written to use Safe version 1 because you will need to
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makes changes.
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=head2 Methods in class Safe
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To create a new compartment, use
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$cpt = new Safe;
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Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
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to use for the compartment (defaults to "Safe::Root0", incremented for
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each new compartment).
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Note that version 1.00 of the Safe module supported a second optional
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parameter, MASK. That functionality has been withdrawn pending deeper
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consideration. Use the permit and deny methods described below.
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The following methods can then be used on the compartment
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object returned by the above constructor. The object argument
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is implicit in each case.
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=over 8
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=item permit (OP, ...)
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Permit the listed operators to be used when compiling code in the
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compartment (in I<addition> to any operators already permitted).
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=item permit_only (OP, ...)
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Permit I<only> the listed operators to be used when compiling code in
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the compartment (I<no> other operators are permitted).
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=item deny (OP, ...)
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Deny the listed operators from being used when compiling code in the
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compartment (other operators may still be permitted).
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=item deny_only (OP, ...)
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Deny I<only> the listed operators from being used when compiling code
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in the compartment (I<all> other operators will be permitted).
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=item trap (OP, ...)
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=item untrap (OP, ...)
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The trap and untrap methods are synonyms for deny and permit
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respectfully.
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=item share (NAME, ...)
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This shares the variable(s) in the argument list with the compartment.
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This is almost identical to exporting variables using the L<Exporter(3)>
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module.
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Each NAME must be the B<name> of a variable, typically with the leading
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type identifier included. A bareword is treated as a function name.
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Examples of legal names are '$foo' for a scalar, '@foo' for an
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array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
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for a glob (i.e. all symbol table entries associated with "foo",
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including scalar, array, hash, sub and filehandle).
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Each NAME is assumed to be in the calling package. See share_from
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for an alternative method (which share uses).
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=item share_from (PACKAGE, ARRAYREF)
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This method is similar to share() but allows you to explicitly name the
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package that symbols should be shared from. The symbol names (including
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type characters) are supplied as an array reference.
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$safe->share_from('main', [ '$foo', '%bar', 'func' ]);
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=item varglob (VARNAME)
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This returns a glob reference for the symbol table entry of VARNAME in
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the package of the compartment. VARNAME must be the B<name> of a
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variable without any leading type marker. For example,
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$cpt = new Safe 'Root';
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$Root::foo = "Hello world";
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# Equivalent version which doesn't need to know $cpt's package name:
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${$cpt->varglob('foo')} = "Hello world";
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=item reval (STRING)
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This evaluates STRING as perl code inside the compartment.
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The code can only see the compartment's namespace (as returned by the
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B<root> method). The compartment's root package appears to be the
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C<main::> package to the code inside the compartment.
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Any attempt by the code in STRING to use an operator which is not permitted
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by the compartment will cause an error (at run-time of the main program
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but at compile-time for the code in STRING). The error is of the form
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"%s trapped by operation mask operation...".
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If an operation is trapped in this way, then the code in STRING will
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not be executed. If such a trapped operation occurs or any other
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compile-time or return error, then $@ is set to the error message, just
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as with an eval().
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If there is no error, then the method returns the value of the last
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expression evaluated, or a return statement may be used, just as with
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subroutines and B<eval()>. The context (list or scalar) is determined
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by the caller as usual.
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This behaviour differs from the beta distribution of the Safe extension
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where earlier versions of perl made it hard to mimic the return
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behaviour of the eval() command and the context was always scalar.
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Some points to note:
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If the entereval op is permitted then the code can use eval "..." to
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'hide' code which might use denied ops. This is not a major problem
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since when the code tries to execute the eval it will fail because the
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opmask is still in effect. However this technique would allow clever,
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and possibly harmful, code to 'probe' the boundaries of what is
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possible.
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Any string eval which is executed by code executing in a compartment,
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or by code called from code executing in a compartment, will be eval'd
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in the namespace of the compartment. This is potentially a serious
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problem.
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Consider a function foo() in package pkg compiled outside a compartment
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but shared with it. Assume the compartment has a root package called
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'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
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normally, $pkg::foo will be set to 1. If foo() is called from the
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compartment (by whatever means) then instead of setting $pkg::foo, the
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eval will actually set $Root::pkg::foo.
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This can easily be demonstrated by using a module, such as the Socket
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module, which uses eval "..." as part of an AUTOLOAD function. You can
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'use' the module outside the compartment and share an (autoloaded)
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function with the compartment. If an autoload is triggered by code in
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the compartment, or by any code anywhere that is called by any means
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from the compartment, then the eval in the Socket module's AUTOLOAD
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function happens in the namespace of the compartment. Any variables
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created or used by the eval'd code are now under the control of
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the code in the compartment.
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A similar effect applies to I<all> runtime symbol lookups in code
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called from a compartment but not compiled within it.
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=item rdo (FILENAME)
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This evaluates the contents of file FILENAME inside the compartment.
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See above documentation on the B<reval> method for further details.
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=item root (NAMESPACE)
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This method returns the name of the package that is the root of the
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compartment's namespace.
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Note that this behaviour differs from version 1.00 of the Safe module
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where the root module could be used to change the namespace. That
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functionality has been withdrawn pending deeper consideration.
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=item mask (MASK)
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This is a get-or-set method for the compartment's operator mask.
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With no MASK argument present, it returns the current operator mask of
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the compartment.
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With the MASK argument present, it sets the operator mask for the
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compartment (equivalent to calling the deny_only method).
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=back
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=head2 Some Safety Issues
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This section is currently just an outline of some of the things code in
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a compartment might do (intentionally or unintentionally) which can
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have an effect outside the compartment.
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=over 8
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=item Memory
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Consuming all (or nearly all) available memory.
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=item CPU
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Causing infinite loops etc.
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=item Snooping
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Copying private information out of your system. Even something as
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simple as your user name is of value to others. Much useful information
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could be gleaned from your environment variables for example.
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=item Signals
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Causing signals (especially SIGFPE and SIGALARM) to affect your process.
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Setting up a signal handler will need to be carefully considered
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and controlled. What mask is in effect when a signal handler
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gets called? If a user can get an imported function to get an
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exception and call the user's signal handler, does that user's
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restricted mask get re-instated before the handler is called?
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Does an imported handler get called with its original mask or
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the user's one?
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=item State Changes
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Ops such as chdir obviously effect the process as a whole and not just
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the code in the compartment. Ops such as rand and srand have a similar
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but more subtle effect.
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=back
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=head2 AUTHOR
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Originally designed and implemented by Malcolm Beattie,
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mbeattie@sable.ox.ac.uk.
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Reworked to use the Opcode module and other changes added by Tim Bunce
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E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.
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=cut
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