6 $Safe::VERSION = "2.09";
11 opset opset_to_ops opmask_add
12 empty_opset full_opset invert_opset verify_opset
13 opdesc opcodes opmask define_optag opset_to_hex
16 *ops_to_opset = \&opset; # Temporary alias for old Penguins
20 my $default_share = ['*_']; #, '*main::'];
23 my($class, $root, $mask) = @_;
28 croak "Can't use \"$root\" as root name"
29 if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
34 $obj->{Root} = "Safe::Root".$default_root++;
38 # use permit/deny methods instead till interface issues resolved
39 # XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...;
40 croak "Mask parameter to new no longer supported" if defined $mask;
41 $obj->permit_only(':default');
43 # We must share $_ and @_ with the compartment or else ops such
44 # as split, length and so on won't default to $_ properly, nor
45 # will passing argument to subroutines work (via @_). In fact,
46 # for reasons I don't completely understand, we need to share
47 # the whole glob *_ rather than $_ and @_ separately, otherwise
48 # @_ in non default packages within the compartment don't work.
49 $obj->share_from('main', $default_share);
50 Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04);
56 $obj->erase('DESTROY') if $obj->{Erase};
60 my ($obj, $action) = @_;
61 my $pkg = $obj->root();
65 $pkg = "main::$pkg\::"; # expand to full symbol table name
66 ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
68 # The 'my $foo' is needed! Without it you get an
69 # 'Attempt to free unreferenced scalar' warning!
70 my $stem_symtab = *{$stem}{HASH};
72 #warn "erase($pkg) stem=$stem, leaf=$leaf";
73 #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
74 # ", join(', ', %$stem_symtab),"\n";
76 # delete $stem_symtab->{$leaf};
78 my $leaf_glob = $stem_symtab->{$leaf};
79 my $leaf_symtab = *{$leaf_glob}{HASH};
80 # warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
82 #delete $leaf_symtab->{'__ANON__'};
83 #delete $leaf_symtab->{'foo'};
84 #delete $leaf_symtab->{'main::'};
85 # my $foo = undef ${"$stem\::"}{"$leaf\::"};
87 if ($action and $action eq 'DESTROY') {
88 delete $stem_symtab->{$leaf};
90 $obj->share_from('main', $default_share);
104 croak("Safe root method now read-only") if @_;
111 return $obj->{Mask} unless @_;
115 # v1 compatibility methods
116 sub trap { shift->deny(@_) }
117 sub untrap { shift->permit(@_) }
121 $obj->{Mask} |= opset(@_);
125 $obj->{Mask} = opset(@_);
131 $obj->{Mask} &= invert_opset opset(@_);
135 $obj->{Mask} = invert_opset opset(@_);
141 print opset_to_hex($obj->{Mask}),"\n";
147 my($obj, @vars) = @_;
148 $obj->share_from(scalar(caller), \@vars);
155 my $no_record = shift || 0;
156 my $root = $obj->root();
157 croak("vars not an array ref") unless ref $vars eq 'ARRAY';
159 # Check that 'from' package actually exists
160 croak("Package \"$pkg\" does not exist")
161 unless keys %{"$pkg\::"};
163 foreach $arg (@$vars) {
164 # catch some $safe->share($var) errors:
165 croak("'$arg' not a valid symbol table name")
166 unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/
169 $type = $1 if ($var = $arg) =~ s/^(\W)//;
170 # warn "share_from $pkg $type $var";
171 *{$root."::$var"} = (!$type) ? \&{$pkg."::$var"}
172 : ($type eq '&') ? \&{$pkg."::$var"}
173 : ($type eq '$') ? \${$pkg."::$var"}
174 : ($type eq '@') ? \@{$pkg."::$var"}
175 : ($type eq '%') ? \%{$pkg."::$var"}
176 : ($type eq '*') ? *{$pkg."::$var"}
177 : croak(qq(Can't share "$type$var" of unknown type));
179 $obj->share_record($pkg, $vars) unless $no_record or !$vars;
186 my $shares = \%{$obj->{Shares} ||= {}};
187 # Record shares using keys of $obj->{Shares}. See reinit.
188 @{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
192 my $shares = \%{$obj->{Shares} ||= {}};
194 while(($var, $pkg) = each %$shares) {
195 # warn "share_redo $pkg\:: $var";
196 $obj->share_from($pkg, [ $var ], 1);
200 delete shift->{Shares};
204 my ($obj, $var) = @_;
206 return *{$obj->root()."::$var"};
211 my ($obj, $expr, $strict) = @_;
212 my $root = $obj->{Root};
214 # Create anon sub ref in root of compartment.
215 # Uses a closure (on $expr) to pass in the code to be executed.
216 # (eval on one line to keep line numbers as expected by caller)
217 my $evalcode = sprintf('package %s; sub { @_ = (); eval $expr; }', $root);
220 if ($strict) { use strict; $evalsub = eval $evalcode; }
221 else { no strict; $evalsub = eval $evalcode; }
223 return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
227 my ($obj, $file) = @_;
228 my $root = $obj->{Root};
231 sprintf('package %s; sub { @_ = (); do $file }', $root);
232 return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
242 Safe - Compile and execute code in restricted compartments
248 $compartment = new Safe;
250 $compartment->permit(qw(time sort :browse));
252 $result = $compartment->reval($unsafe_code);
256 The Safe extension module allows the creation of compartments
257 in which perl code can be evaluated. Each compartment has
261 =item a new namespace
263 The "root" of the namespace (i.e. "main::") is changed to a
264 different package and code evaluated in the compartment cannot
265 refer to variables outside this namespace, even with run-time
266 glob lookups and other tricks.
268 Code which is compiled outside the compartment can choose to place
269 variables into (or I<share> variables with) the compartment's namespace
270 and only that data will be visible to code evaluated in the
273 By default, the only variables shared with compartments are the
274 "underscore" variables $_ and @_ (and, technically, the less frequently
275 used %_, the _ filehandle and so on). This is because otherwise perl
276 operators which default to $_ will not work and neither will the
277 assignment of arguments to @_ on subroutine entry.
279 =item an operator mask
281 Each compartment has an associated "operator mask". Recall that
282 perl code is compiled into an internal format before execution.
283 Evaluating perl code (e.g. via "eval" or "do 'file'") causes
284 the code to be compiled into an internal format and then,
285 provided there was no error in the compilation, executed.
286 Code evaluated in a compartment compiles subject to the
287 compartment's operator mask. Attempting to evaluate code in a
288 compartment which contains a masked operator will cause the
289 compilation to fail with an error. The code will not be executed.
291 The default operator mask for a newly created compartment is
292 the ':default' optag.
294 It is important that you read the Opcode(3) module documentation
295 for more information, especially for detailed definitions of opnames,
298 Since it is only at the compilation stage that the operator mask
299 applies, controlled access to potentially unsafe operations can
300 be achieved by having a handle to a wrapper subroutine (written
301 outside the compartment) placed into the compartment. For example,
305 # vet arguments and perform potentially unsafe operations
307 $cpt->share('&wrapper');
314 The authors make B<no warranty>, implied or otherwise, about the
315 suitability of this software for safety or security purposes.
317 The authors shall not in any case be liable for special, incidental,
318 consequential, indirect or other similar damages arising from the use
321 Your mileage will vary. If in any doubt B<do not use it>.
324 =head2 RECENT CHANGES
326 The interface to the Safe module has changed quite dramatically since
327 version 1 (as supplied with Perl5.002). Study these pages carefully if
328 you have code written to use Safe version 1 because you will need to
332 =head2 Methods in class Safe
334 To create a new compartment, use
338 Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
339 to use for the compartment (defaults to "Safe::Root0", incremented for
340 each new compartment).
342 Note that version 1.00 of the Safe module supported a second optional
343 parameter, MASK. That functionality has been withdrawn pending deeper
344 consideration. Use the permit and deny methods described below.
346 The following methods can then be used on the compartment
347 object returned by the above constructor. The object argument
348 is implicit in each case.
353 =item permit (OP, ...)
355 Permit the listed operators to be used when compiling code in the
356 compartment (in I<addition> to any operators already permitted).
358 =item permit_only (OP, ...)
360 Permit I<only> the listed operators to be used when compiling code in
361 the compartment (I<no> other operators are permitted).
365 Deny the listed operators from being used when compiling code in the
366 compartment (other operators may still be permitted).
368 =item deny_only (OP, ...)
370 Deny I<only> the listed operators from being used when compiling code
371 in the compartment (I<all> other operators will be permitted).
375 =item untrap (OP, ...)
377 The trap and untrap methods are synonyms for deny and permit
380 =item share (NAME, ...)
382 This shares the variable(s) in the argument list with the compartment.
383 This is almost identical to exporting variables using the L<Exporter>
386 Each NAME must be the B<name> of a non-lexical variable, typically
387 with the leading type identifier included. A bareword is treated as a
390 Examples of legal names are '$foo' for a scalar, '@foo' for an
391 array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
392 for a glob (i.e. all symbol table entries associated with "foo",
393 including scalar, array, hash, sub and filehandle).
395 Each NAME is assumed to be in the calling package. See share_from
396 for an alternative method (which share uses).
398 =item share_from (PACKAGE, ARRAYREF)
400 This method is similar to share() but allows you to explicitly name the
401 package that symbols should be shared from. The symbol names (including
402 type characters) are supplied as an array reference.
404 $safe->share_from('main', [ '$foo', '%bar', 'func' ]);
407 =item varglob (VARNAME)
409 This returns a glob reference for the symbol table entry of VARNAME in
410 the package of the compartment. VARNAME must be the B<name> of a
411 variable without any leading type marker. For example,
413 $cpt = new Safe 'Root';
414 $Root::foo = "Hello world";
415 # Equivalent version which doesn't need to know $cpt's package name:
416 ${$cpt->varglob('foo')} = "Hello world";
421 This evaluates STRING as perl code inside the compartment.
423 The code can only see the compartment's namespace (as returned by the
424 B<root> method). The compartment's root package appears to be the
425 C<main::> package to the code inside the compartment.
427 Any attempt by the code in STRING to use an operator which is not permitted
428 by the compartment will cause an error (at run-time of the main program
429 but at compile-time for the code in STRING). The error is of the form
430 "'%s' trapped by operation mask...".
432 If an operation is trapped in this way, then the code in STRING will
433 not be executed. If such a trapped operation occurs or any other
434 compile-time or return error, then $@ is set to the error message, just
437 If there is no error, then the method returns the value of the last
438 expression evaluated, or a return statement may be used, just as with
439 subroutines and B<eval()>. The context (list or scalar) is determined
440 by the caller as usual.
442 This behaviour differs from the beta distribution of the Safe extension
443 where earlier versions of perl made it hard to mimic the return
444 behaviour of the eval() command and the context was always scalar.
448 If the entereval op is permitted then the code can use eval "..." to
449 'hide' code which might use denied ops. This is not a major problem
450 since when the code tries to execute the eval it will fail because the
451 opmask is still in effect. However this technique would allow clever,
452 and possibly harmful, code to 'probe' the boundaries of what is
455 Any string eval which is executed by code executing in a compartment,
456 or by code called from code executing in a compartment, will be eval'd
457 in the namespace of the compartment. This is potentially a serious
460 Consider a function foo() in package pkg compiled outside a compartment
461 but shared with it. Assume the compartment has a root package called
462 'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
463 normally, $pkg::foo will be set to 1. If foo() is called from the
464 compartment (by whatever means) then instead of setting $pkg::foo, the
465 eval will actually set $Root::pkg::foo.
467 This can easily be demonstrated by using a module, such as the Socket
468 module, which uses eval "..." as part of an AUTOLOAD function. You can
469 'use' the module outside the compartment and share an (autoloaded)
470 function with the compartment. If an autoload is triggered by code in
471 the compartment, or by any code anywhere that is called by any means
472 from the compartment, then the eval in the Socket module's AUTOLOAD
473 function happens in the namespace of the compartment. Any variables
474 created or used by the eval'd code are now under the control of
475 the code in the compartment.
477 A similar effect applies to I<all> runtime symbol lookups in code
478 called from a compartment but not compiled within it.
484 This evaluates the contents of file FILENAME inside the compartment.
485 See above documentation on the B<reval> method for further details.
487 =item root (NAMESPACE)
489 This method returns the name of the package that is the root of the
490 compartment's namespace.
492 Note that this behaviour differs from version 1.00 of the Safe module
493 where the root module could be used to change the namespace. That
494 functionality has been withdrawn pending deeper consideration.
498 This is a get-or-set method for the compartment's operator mask.
500 With no MASK argument present, it returns the current operator mask of
503 With the MASK argument present, it sets the operator mask for the
504 compartment (equivalent to calling the deny_only method).
509 =head2 Some Safety Issues
511 This section is currently just an outline of some of the things code in
512 a compartment might do (intentionally or unintentionally) which can
513 have an effect outside the compartment.
519 Consuming all (or nearly all) available memory.
523 Causing infinite loops etc.
527 Copying private information out of your system. Even something as
528 simple as your user name is of value to others. Much useful information
529 could be gleaned from your environment variables for example.
533 Causing signals (especially SIGFPE and SIGALARM) to affect your process.
535 Setting up a signal handler will need to be carefully considered
536 and controlled. What mask is in effect when a signal handler
537 gets called? If a user can get an imported function to get an
538 exception and call the user's signal handler, does that user's
539 restricted mask get re-instated before the handler is called?
540 Does an imported handler get called with its original mask or
545 Ops such as chdir obviously effect the process as a whole and not just
546 the code in the compartment. Ops such as rand and srand have a similar
547 but more subtle effect.
553 Originally designed and implemented by Malcolm Beattie,
554 mbeattie@sable.ox.ac.uk.
556 Reworked to use the Opcode module and other changes added by Tim Bunce
557 E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.