Annotation of loncom/xml/Safe.pm, revision 1.6
1.1 albertel 1: package Safe;
2:
3: use 5.003_11;
4: use strict;
5:
1.6 ! albertel 6: $Safe::VERSION = "2.09";
1.1 albertel 7:
8: use Carp;
9:
10: use Opcode 1.01, qw(
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
14: );
15:
16: *ops_to_opset = \&opset; # Temporary alias for old Penguins
17:
18:
19: my $default_root = 0;
20: my $default_share = ['*_']; #, '*main::'];
21:
22: sub new {
23: my($class, $root, $mask) = @_;
24: my $obj = {};
25: bless $obj, $class;
26:
27: if (defined($root)) {
28: croak "Can't use \"$root\" as root name"
29: if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
30: $obj->{Root} = $root;
31: $obj->{Erase} = 0;
32: }
33: else {
34: $obj->{Root} = "Safe::Root".$default_root++;
35: $obj->{Erase} = 1;
36: }
37:
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');
42:
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', $default_share);
1.6 ! albertel 50: Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04);
1.1 albertel 51: return $obj;
52: }
53:
54: sub DESTROY {
55: my $obj = shift;
56: $obj->erase('DESTROY') if $obj->{Erase};
57: }
58:
59: sub erase {
60: my ($obj, $action) = @_;
61: my $pkg = $obj->root();
62: my ($stem, $leaf);
63:
64: no strict 'refs';
65: $pkg = "main::$pkg\::"; # expand to full symbol table name
66: ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
67:
68: # The 'my $foo' is needed! Without it you get an
69: # 'Attempt to free unreferenced scalar' warning!
70: my $stem_symtab = *{$stem}{HASH};
71:
72: #warn "erase($pkg) stem=$stem, leaf=$leaf";
73: #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
74: # ", join(', ', %$stem_symtab),"\n";
75:
76: # delete $stem_symtab->{$leaf};
77:
78: my $leaf_glob = $stem_symtab->{$leaf};
79: my $leaf_symtab = *{$leaf_glob}{HASH};
80: # warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
81: %$leaf_symtab = ();
82: #delete $leaf_symtab->{'__ANON__'};
83: #delete $leaf_symtab->{'foo'};
84: #delete $leaf_symtab->{'main::'};
85: # my $foo = undef ${"$stem\::"}{"$leaf\::"};
86:
87: if ($action and $action eq 'DESTROY') {
88: delete $stem_symtab->{$leaf};
89: } else {
90: $obj->share_from('main', $default_share);
91: }
92: 1;
93: }
94:
95:
96: sub reinit {
97: my $obj= shift;
98: $obj->erase;
99: $obj->share_redo;
100: }
101:
102: sub root {
103: my $obj = shift;
104: croak("Safe root method now read-only") if @_;
105: return $obj->{Root};
106: }
107:
108:
109: sub mask {
110: my $obj = shift;
111: return $obj->{Mask} unless @_;
112: $obj->deny_only(@_);
113: }
114:
115: # v1 compatibility methods
116: sub trap { shift->deny(@_) }
117: sub untrap { shift->permit(@_) }
118:
119: sub deny {
120: my $obj = shift;
121: $obj->{Mask} |= opset(@_);
122: }
123: sub deny_only {
124: my $obj = shift;
125: $obj->{Mask} = opset(@_);
126: }
127:
128: sub permit {
129: my $obj = shift;
130: # XXX needs testing
131: $obj->{Mask} &= invert_opset opset(@_);
132: }
133: sub permit_only {
134: my $obj = shift;
135: $obj->{Mask} = invert_opset opset(@_);
136: }
137:
138:
139: sub dump_mask {
140: my $obj = shift;
141: print opset_to_hex($obj->{Mask}),"\n";
142: }
143:
144:
145:
146: sub share {
147: my($obj, @vars) = @_;
148: $obj->share_from(scalar(caller), \@vars);
149: }
150:
151: sub share_from {
152: my $obj = shift;
153: my $pkg = shift;
154: my $vars = shift;
155: my $no_record = shift || 0;
156: my $root = $obj->root();
157: croak("vars not an array ref") unless ref $vars eq 'ARRAY';
1.6 ! albertel 158: no strict 'refs';
1.1 albertel 159: # Check that 'from' package actually exists
160: croak("Package \"$pkg\" does not exist")
161: unless keys %{"$pkg\::"};
162: my $arg;
163: foreach $arg (@$vars) {
164: # catch some $safe->share($var) errors:
165: croak("'$arg' not a valid symbol table name")
166: unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/
167: or $arg =~ /^\$\W$/;
168: my ($var, $type);
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));
178: }
179: $obj->share_record($pkg, $vars) unless $no_record or !$vars;
180: }
181:
182: sub share_record {
183: my $obj = shift;
184: my $pkg = shift;
185: my $vars = shift;
186: my $shares = \%{$obj->{Shares} ||= {}};
187: # Record shares using keys of $obj->{Shares}. See reinit.
188: @{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
189: }
190: sub share_redo {
191: my $obj = shift;
192: my $shares = \%{$obj->{Shares} ||= {}};
1.6 ! albertel 193: my($var, $pkg);
1.1 albertel 194: while(($var, $pkg) = each %$shares) {
195: # warn "share_redo $pkg\:: $var";
196: $obj->share_from($pkg, [ $var ], 1);
197: }
198: }
199: sub share_forget {
200: delete shift->{Shares};
201: }
202:
203: sub varglob {
204: my ($obj, $var) = @_;
205: no strict 'refs';
206: return *{$obj->root()."::$var"};
207: }
208:
209:
210: sub reval {
1.6 ! albertel 211: my ($obj, $expr, $strict) = @_;
1.1 albertel 212: my $root = $obj->{Root};
213:
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)
1.6 ! albertel 217: my $evalcode = sprintf('package %s; sub { @_ = (); eval $expr; }', $root);
1.1 albertel 218: my $evalsub;
219:
1.6 ! albertel 220: if ($strict) { use strict; $evalsub = eval $evalcode; }
! 221: else { no strict; $evalsub = eval $evalcode; }
1.1 albertel 222:
223: return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
224: }
225:
226: sub rdo {
227: my ($obj, $file) = @_;
228: my $root = $obj->{Root};
229:
230: my $evalsub = eval
1.6 ! albertel 231: sprintf('package %s; sub { @_ = (); do $file }', $root);
1.1 albertel 232: return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
233: }
234:
235:
236: 1;
237:
238: __END__
239:
240: =head1 NAME
241:
242: Safe - Compile and execute code in restricted compartments
243:
244: =head1 SYNOPSIS
245:
246: use Safe;
247:
248: $compartment = new Safe;
249:
250: $compartment->permit(qw(time sort :browse));
251:
252: $result = $compartment->reval($unsafe_code);
253:
254: =head1 DESCRIPTION
255:
256: The Safe extension module allows the creation of compartments
257: in which perl code can be evaluated. Each compartment has
258:
259: =over 8
260:
261: =item a new namespace
262:
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.
267:
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
271: compartment.
272:
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.
278:
279: =item an operator mask
280:
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.
290:
291: The default operator mask for a newly created compartment is
292: the ':default' optag.
293:
294: It is important that you read the Opcode(3) module documentation
295: for more information, especially for detailed definitions of opnames,
296: optags and opsets.
297:
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,
302:
303: $cpt = new Safe;
304: sub wrapper {
305: # vet arguments and perform potentially unsafe operations
306: }
307: $cpt->share('&wrapper');
308:
309: =back
310:
311:
312: =head1 WARNING
313:
314: The authors make B<no warranty>, implied or otherwise, about the
315: suitability of this software for safety or security purposes.
316:
317: The authors shall not in any case be liable for special, incidental,
318: consequential, indirect or other similar damages arising from the use
319: of this software.
320:
321: Your mileage will vary. If in any doubt B<do not use it>.
322:
323:
324: =head2 RECENT CHANGES
325:
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
329: makes changes.
330:
331:
332: =head2 Methods in class Safe
333:
334: To create a new compartment, use
335:
336: $cpt = new Safe;
337:
338: Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
339: to use for the compartment (defaults to "Safe::Root0", incremented for
340: each new compartment).
341:
342: Note that version 1.00 of the Safe module supported a second optional
343: parameter, MASK. That functionality has been withdrawn pending deeper
344: consideration. Use the permit and deny methods described below.
345:
346: The following methods can then be used on the compartment
347: object returned by the above constructor. The object argument
348: is implicit in each case.
349:
350:
351: =over 8
352:
353: =item permit (OP, ...)
354:
355: Permit the listed operators to be used when compiling code in the
356: compartment (in I<addition> to any operators already permitted).
357:
358: =item permit_only (OP, ...)
359:
360: Permit I<only> the listed operators to be used when compiling code in
361: the compartment (I<no> other operators are permitted).
362:
363: =item deny (OP, ...)
364:
365: Deny the listed operators from being used when compiling code in the
366: compartment (other operators may still be permitted).
367:
368: =item deny_only (OP, ...)
369:
370: Deny I<only> the listed operators from being used when compiling code
371: in the compartment (I<all> other operators will be permitted).
372:
373: =item trap (OP, ...)
374:
375: =item untrap (OP, ...)
376:
377: The trap and untrap methods are synonyms for deny and permit
378: respectfully.
379:
380: =item share (NAME, ...)
381:
382: This shares the variable(s) in the argument list with the compartment.
1.6 ! albertel 383: This is almost identical to exporting variables using the L<Exporter>
1.1 albertel 384: module.
385:
1.6 ! albertel 386: Each NAME must be the B<name> of a non-lexical variable, typically
! 387: with the leading type identifier included. A bareword is treated as a
! 388: function name.
1.1 albertel 389:
390: Examples of legal names are '$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).
394:
395: Each NAME is assumed to be in the calling package. See share_from
396: for an alternative method (which share uses).
397:
398: =item share_from (PACKAGE, ARRAYREF)
399:
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.
403:
404: $safe->share_from('main', [ '$foo', '%bar', 'func' ]);
405:
406:
407: =item varglob (VARNAME)
408:
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,
412:
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";
417:
418:
419: =item reval (STRING)
420:
421: This evaluates STRING as perl code inside the compartment.
422:
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.
426:
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
1.6 ! albertel 430: "'%s' trapped by operation mask...".
1.1 albertel 431:
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 $@ is set to the error message, just
435: as with an eval().
436:
437: If there is no error, then the method returns the value of the last
438: expression evaluated, or a return statement may be used, just as with
439: subroutines and B<eval()>. The context (list or scalar) is determined
440: by the caller as usual.
441:
442: This behaviour differs from the beta distribution of the Safe extension
443: where earlier versions of perl made it hard to mimic the return
444: behaviour of the eval() command and the context was always scalar.
445:
446: Some points to note:
447:
448: If the entereval op is permitted then the code can use eval "..." to
449: 'hide' code which might use denied ops. This is not a major problem
450: since when the code tries to execute the eval it will fail because the
451: opmask is still in effect. However this technique would allow clever,
452: and possibly harmful, code to 'probe' the boundaries of what is
453: possible.
454:
455: Any string eval which is executed by code executing in a compartment,
456: or by code called from code executing in a compartment, will be eval'd
457: in the namespace of the compartment. This is potentially a serious
458: problem.
459:
460: Consider a function foo() in package pkg compiled outside a compartment
461: but shared with it. Assume the compartment has a root package called
462: 'Root'. If foo() contains an eval statement like eval '$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.
466:
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.
476:
477: A similar effect applies to I<all> runtime symbol lookups in code
478: called from a compartment but not compiled within it.
479:
480:
481:
482: =item rdo (FILENAME)
483:
484: This evaluates the contents of file FILENAME inside the compartment.
485: See above documentation on the B<reval> method for further details.
486:
487: =item root (NAMESPACE)
488:
489: This method returns the name of the package that is the root of the
490: compartment's namespace.
491:
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.
495:
496: =item mask (MASK)
497:
498: This is a get-or-set method for the compartment's operator mask.
499:
500: With no MASK argument present, it returns the current operator mask of
501: the compartment.
502:
503: With the MASK argument present, it sets the operator mask for the
504: compartment (equivalent to calling the deny_only method).
505:
506: =back
507:
508:
509: =head2 Some Safety Issues
510:
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.
514:
515: =over 8
516:
517: =item Memory
518:
519: Consuming all (or nearly all) available memory.
520:
521: =item CPU
522:
523: Causing infinite loops etc.
524:
525: =item Snooping
526:
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.
530:
531: =item Signals
532:
533: Causing signals (especially SIGFPE and SIGALARM) to affect your process.
534:
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
541: the user's one?
542:
543: =item State Changes
544:
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.
548:
549: =back
550:
551: =head2 AUTHOR
552:
553: Originally designed and implemented by Malcolm Beattie,
554: mbeattie@sable.ox.ac.uk.
555:
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>.
558:
559: =cut
560:
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