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Carp was mostly unusable with Safe because it may require
[perl5.git] / ext / Opcode / Safe.pm
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1package Safe;
2
5f05dabc 3use 5.003_11;
2ded1cc1 4use strict;
2ded1cc1 5
b27d3831 6$Safe::VERSION = "2.10_01";
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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
13sub 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}
2ded1cc1 27
5f05dabc 28use Carp;
b27d3831 29use Carp::Heavy;
5f05dabc 30
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31use 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
40my $default_root = 0;
41my $default_share = ['*_']; #, '*main::'];
42
43sub new {
44 my($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', $default_share);
ac5e3691 71 Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04);
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72 return $obj;
73}
74
75sub DESTROY {
76 my $obj = shift;
4d8e9581 77 $obj->erase('DESTROY') if $obj->{Erase};
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78}
79
80sub erase {
4d8e9581 81 my ($obj, $action) = @_;
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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
4d8e9581 97# delete $stem_symtab->{$leaf};
2ded1cc1 98
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99 my $leaf_glob = $stem_symtab->{$leaf};
100 my $leaf_symtab = *{$leaf_glob}{HASH};
2ded1cc1 101# warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
4d8e9581 102 %$leaf_symtab = ();
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103 #delete $leaf_symtab->{'__ANON__'};
104 #delete $leaf_symtab->{'foo'};
105 #delete $leaf_symtab->{'main::'};
106# my $foo = undef ${"$stem\::"}{"$leaf\::"};
107
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108 if ($action and $action eq 'DESTROY') {
109 delete $stem_symtab->{$leaf};
110 } else {
111 $obj->share_from('main', $default_share);
112 }
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113 1;
114}
115
116
117sub reinit {
118 my $obj= shift;
119 $obj->erase;
120 $obj->share_redo;
121}
122
123sub root {
124 my $obj = shift;
125 croak("Safe root method now read-only") if @_;
126 return $obj->{Root};
127}
128
129
130sub mask {
131 my $obj = shift;
132 return $obj->{Mask} unless @_;
133 $obj->deny_only(@_);
134}
135
136# v1 compatibility methods
137sub trap { shift->deny(@_) }
138sub untrap { shift->permit(@_) }
139
140sub deny {
141 my $obj = shift;
142 $obj->{Mask} |= opset(@_);
143}
144sub deny_only {
145 my $obj = shift;
146 $obj->{Mask} = opset(@_);
147}
148
149sub permit {
150 my $obj = shift;
151 # XXX needs testing
152 $obj->{Mask} &= invert_opset opset(@_);
153}
154sub permit_only {
155 my $obj = shift;
156 $obj->{Mask} = invert_opset opset(@_);
157}
158
159
160sub dump_mask {
161 my $obj = shift;
162 print opset_to_hex($obj->{Mask}),"\n";
163}
164
165
166
167sub share {
168 my($obj, @vars) = @_;
169 $obj->share_from(scalar(caller), \@vars);
170}
171
172sub share_from {
173 my $obj = shift;
174 my $pkg = shift;
175 my $vars = shift;
176 my $no_record = shift || 0;
50fc18f7 177 my $root = $obj->root();
2ded1cc1 178 croak("vars not an array ref") unless ref $vars eq 'ARRAY';
d00660f4 179 no strict 'refs';
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180 # Check that 'from' package actually exists
181 croak("Package \"$pkg\" does not exist")
182 unless keys %{"$pkg\::"};
3fe9a6f1 183 my $arg;
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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 $arg =~ /^\$\W$/;
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189 my ($var, $type);
190 $type = $1 if ($var = $arg) =~ s/^(\W)//;
191 # warn "share_from $pkg $type $var";
50fc18f7 192 *{$root."::$var"} = (!$type) ? \&{$pkg."::$var"}
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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));
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199 }
200 $obj->share_record($pkg, $vars) unless $no_record or !$vars;
201}
202
203sub 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}
211sub share_redo {
212 my $obj = shift;
213 my $shares = \%{$obj->{Shares} ||= {}};
d00660f4 214 my($var, $pkg);
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215 while(($var, $pkg) = each %$shares) {
216 # warn "share_redo $pkg\:: $var";
217 $obj->share_from($pkg, [ $var ], 1);
218 }
219}
220sub share_forget {
221 delete shift->{Shares};
222}
223
224sub varglob {
225 my ($obj, $var) = @_;
226 no strict 'refs';
227 return *{$obj->root()."::$var"};
228}
229
230
231sub reval {
232 my ($obj, $expr, $strict) = @_;
50fc18f7 233 my $root = $obj->{Root};
2ded1cc1 234
35ed0d3c 235 my $evalsub = lexless_anon_sub($root,$strict, $expr);
50fc18f7 236 return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
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237}
238
239sub rdo {
240 my ($obj, $file) = @_;
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241 my $root = $obj->{Root};
242
243 my $evalsub = eval
d00660f4 244 sprintf('package %s; sub { @_ = (); do $file }', $root);
50fc18f7 245 return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
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246}
247
248
2491;
250
3e92a254 251__END__
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252
253=head1 NAME
254
255Safe - 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
269The Safe extension module allows the creation of compartments
270in which perl code can be evaluated. Each compartment has
271
272=over 8
273
274=item a new namespace
275
276The "root" of the namespace (i.e. "main::") is changed to a
277different package and code evaluated in the compartment cannot
278refer to variables outside this namespace, even with run-time
279glob lookups and other tricks.
280
281Code which is compiled outside the compartment can choose to place
282variables into (or I<share> variables with) the compartment's namespace
283and only that data will be visible to code evaluated in the
284compartment.
285
286By default, the only variables shared with compartments are the
287"underscore" variables $_ and @_ (and, technically, the less frequently
288used %_, the _ filehandle and so on). This is because otherwise perl
289operators which default to $_ will not work and neither will the
290assignment of arguments to @_ on subroutine entry.
291
292=item an operator mask
293
294Each compartment has an associated "operator mask". Recall that
295perl code is compiled into an internal format before execution.
296Evaluating perl code (e.g. via "eval" or "do 'file'") causes
297the code to be compiled into an internal format and then,
298provided there was no error in the compilation, executed.
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299Code evaluated in a compartment compiles subject to the
300compartment's operator mask. Attempting to evaluate code in a
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301compartment which contains a masked operator will cause the
302compilation to fail with an error. The code will not be executed.
303
304The default operator mask for a newly created compartment is
305the ':default' optag.
306
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307It is important that you read the Opcode(3) module documentation
308for more information, especially for detailed definitions of opnames,
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309optags and opsets.
310
311Since it is only at the compilation stage that the operator mask
312applies, controlled access to potentially unsafe operations can
313be achieved by having a handle to a wrapper subroutine (written
314outside 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
327The authors make B<no warranty>, implied or otherwise, about the
328suitability of this software for safety or security purposes.
329
330The authors shall not in any case be liable for special, incidental,
331consequential, indirect or other similar damages arising from the use
332of this software.
333
334Your mileage will vary. If in any doubt B<do not use it>.
335
336
337=head2 RECENT CHANGES
338
339The interface to the Safe module has changed quite dramatically since
340version 1 (as supplied with Perl5.002). Study these pages carefully if
341you have code written to use Safe version 1 because you will need to
342makes changes.
343
344
345=head2 Methods in class Safe
346
347To create a new compartment, use
348
349 $cpt = new Safe;
350
351Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
352to use for the compartment (defaults to "Safe::Root0", incremented for
353each new compartment).
354
355Note that version 1.00 of the Safe module supported a second optional
356parameter, MASK. That functionality has been withdrawn pending deeper
357consideration. Use the permit and deny methods described below.
358
359The following methods can then be used on the compartment
360object returned by the above constructor. The object argument
361is implicit in each case.
362
363
364=over 8
365
366=item permit (OP, ...)
367
368Permit the listed operators to be used when compiling code in the
369compartment (in I<addition> to any operators already permitted).
370
371=item permit_only (OP, ...)
372
373Permit I<only> the listed operators to be used when compiling code in
374the compartment (I<no> other operators are permitted).
375
376=item deny (OP, ...)
377
378Deny the listed operators from being used when compiling code in the
379compartment (other operators may still be permitted).
380
381=item deny_only (OP, ...)
382
383Deny I<only> the listed operators from being used when compiling code
384in the compartment (I<all> other operators will be permitted).
385
386=item trap (OP, ...)
387
388=item untrap (OP, ...)
389
390The trap and untrap methods are synonyms for deny and permit
391respectfully.
392
393=item share (NAME, ...)
394
395This shares the variable(s) in the argument list with the compartment.
5f944aa8 396This is almost identical to exporting variables using the L<Exporter>
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397module.
398
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399Each NAME must be the B<name> of a non-lexical variable, typically
400with the leading type identifier included. A bareword is treated as a
401function name.
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402
403Examples of legal names are '$foo' for a scalar, '@foo' for an
404array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
405for a glob (i.e. all symbol table entries associated with "foo",
406including scalar, array, hash, sub and filehandle).
407
408Each NAME is assumed to be in the calling package. See share_from
409for an alternative method (which share uses).
410
411=item share_from (PACKAGE, ARRAYREF)
412
413This method is similar to share() but allows you to explicitly name the
414package that symbols should be shared from. The symbol names (including
415type characters) are supplied as an array reference.
416
417 $safe->share_from('main', [ '$foo', '%bar', 'func' ]);
418
419
420=item varglob (VARNAME)
421
422This returns a glob reference for the symbol table entry of VARNAME in
423the package of the compartment. VARNAME must be the B<name> of a
424variable 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
434This evaluates STRING as perl code inside the compartment.
435
436The code can only see the compartment's namespace (as returned by the
437B<root> method). The compartment's root package appears to be the
438C<main::> package to the code inside the compartment.
439
440Any attempt by the code in STRING to use an operator which is not permitted
441by the compartment will cause an error (at run-time of the main program
442but at compile-time for the code in STRING). The error is of the form
cb77fdf0 443"'%s' trapped by operation mask...".
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444
445If an operation is trapped in this way, then the code in STRING will
446not be executed. If such a trapped operation occurs or any other
447compile-time or return error, then $@ is set to the error message, just
448as with an eval().
449
450If there is no error, then the method returns the value of the last
451expression evaluated, or a return statement may be used, just as with
452subroutines and B<eval()>. The context (list or scalar) is determined
453by the caller as usual.
454
455This behaviour differs from the beta distribution of the Safe extension
456where earlier versions of perl made it hard to mimic the return
457behaviour of the eval() command and the context was always scalar.
458
459Some points to note:
460
461If the entereval op is permitted then the code can use eval "..." to
462'hide' code which might use denied ops. This is not a major problem
463since when the code tries to execute the eval it will fail because the
464opmask is still in effect. However this technique would allow clever,
465and possibly harmful, code to 'probe' the boundaries of what is
466possible.
467
468Any string eval which is executed by code executing in a compartment,
469or by code called from code executing in a compartment, will be eval'd
470in the namespace of the compartment. This is potentially a serious
471problem.
472
473Consider a function foo() in package pkg compiled outside a compartment
474but shared with it. Assume the compartment has a root package called
1fef88e7 475'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
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476normally, $pkg::foo will be set to 1. If foo() is called from the
477compartment (by whatever means) then instead of setting $pkg::foo, the
478eval will actually set $Root::pkg::foo.
479
480This can easily be demonstrated by using a module, such as the Socket
481module, which uses eval "..." as part of an AUTOLOAD function. You can
482'use' the module outside the compartment and share an (autoloaded)
483function with the compartment. If an autoload is triggered by code in
484the compartment, or by any code anywhere that is called by any means
485from the compartment, then the eval in the Socket module's AUTOLOAD
486function happens in the namespace of the compartment. Any variables
487created or used by the eval'd code are now under the control of
488the code in the compartment.
489
490A similar effect applies to I<all> runtime symbol lookups in code
491called from a compartment but not compiled within it.
492
493
494
495=item rdo (FILENAME)
496
497This evaluates the contents of file FILENAME inside the compartment.
498See above documentation on the B<reval> method for further details.
499
500=item root (NAMESPACE)
501
502This method returns the name of the package that is the root of the
503compartment's namespace.
504
505Note that this behaviour differs from version 1.00 of the Safe module
506where the root module could be used to change the namespace. That
507functionality has been withdrawn pending deeper consideration.
508
509=item mask (MASK)
510
511This is a get-or-set method for the compartment's operator mask.
512
513With no MASK argument present, it returns the current operator mask of
514the compartment.
515
516With the MASK argument present, it sets the operator mask for the
517compartment (equivalent to calling the deny_only method).
518
519=back
520
521
522=head2 Some Safety Issues
523
524This section is currently just an outline of some of the things code in
525a compartment might do (intentionally or unintentionally) which can
526have an effect outside the compartment.
527
528=over 8
529
530=item Memory
531
532Consuming all (or nearly all) available memory.
533
534=item CPU
535
536Causing infinite loops etc.
537
538=item Snooping
539
540Copying private information out of your system. Even something as
541simple as your user name is of value to others. Much useful information
542could be gleaned from your environment variables for example.
543
544=item Signals
545
546Causing signals (especially SIGFPE and SIGALARM) to affect your process.
547
548Setting up a signal handler will need to be carefully considered
549and controlled. What mask is in effect when a signal handler
550gets called? If a user can get an imported function to get an
551exception and call the user's signal handler, does that user's
552restricted mask get re-instated before the handler is called?
553Does an imported handler get called with its original mask or
554the user's one?
555
556=item State Changes
557
558Ops such as chdir obviously effect the process as a whole and not just
559the code in the compartment. Ops such as rand and srand have a similar
560but more subtle effect.
561
562=back
563
564=head2 AUTHOR
565
566Originally designed and implemented by Malcolm Beattie,
567mbeattie@sable.ox.ac.uk.
568
569Reworked to use the Opcode module and other changes added by Tim Bunce
1fef88e7 570E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.
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571
572=cut
573