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920dae64 AT |
1 | package Safe; |
2 | ||
3 | use 5.003_11; | |
4 | use strict; | |
5 | ||
6 | $Safe::VERSION = "2.12"; | |
7 | ||
8 | # *** Don't declare any lexicals above this point *** | |
9 | # | |
10 | # This function should return a closure which contains an eval that can't | |
11 | # see any lexicals in scope (apart from __ExPr__ which is unavoidable) | |
12 | ||
13 | sub lexless_anon_sub { | |
14 | # $_[0] is package; | |
15 | # $_[1] is strict flag; | |
16 | my $__ExPr__ = $_[2]; # must be a lexical to create the closure that | |
17 | # can be used to pass the value into the safe | |
18 | # world | |
19 | ||
20 | # Create anon sub ref in root of compartment. | |
21 | # Uses a closure (on $__ExPr__) to pass in the code to be executed. | |
22 | # (eval on one line to keep line numbers as expected by caller) | |
23 | eval sprintf | |
24 | 'package %s; %s strict; sub { @_=(); eval q[my $__ExPr__;] . $__ExPr__; }', | |
25 | $_[0], $_[1] ? 'use' : 'no'; | |
26 | } | |
27 | ||
28 | use Carp; | |
29 | use Carp::Heavy; | |
30 | ||
31 | use Opcode 1.01, qw( | |
32 | opset opset_to_ops opmask_add | |
33 | empty_opset full_opset invert_opset verify_opset | |
34 | opdesc opcodes opmask define_optag opset_to_hex | |
35 | ); | |
36 | ||
37 | *ops_to_opset = \&opset; # Temporary alias for old Penguins | |
38 | ||
39 | ||
40 | my $default_root = 0; | |
41 | my $default_share = ['*_']; #, '*main::']; | |
42 | ||
43 | sub new { | |
44 | my($class, $root, $mask) = @_; | |
45 | my $obj = {}; | |
46 | bless $obj, $class; | |
47 | ||
48 | if (defined($root)) { | |
49 | croak "Can't use \"$root\" as root name" | |
50 | if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/; | |
51 | $obj->{Root} = $root; | |
52 | $obj->{Erase} = 0; | |
53 | } | |
54 | else { | |
55 | $obj->{Root} = "Safe::Root".$default_root++; | |
56 | $obj->{Erase} = 1; | |
57 | } | |
58 | ||
59 | # use permit/deny methods instead till interface issues resolved | |
60 | # XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...; | |
61 | croak "Mask parameter to new no longer supported" if defined $mask; | |
62 | $obj->permit_only(':default'); | |
63 | ||
64 | # We must share $_ and @_ with the compartment or else ops such | |
65 | # as split, length and so on won't default to $_ properly, nor | |
66 | # will passing argument to subroutines work (via @_). In fact, | |
67 | # for reasons I don't completely understand, we need to share | |
68 | # the whole glob *_ rather than $_ and @_ separately, otherwise | |
69 | # @_ in non default packages within the compartment don't work. | |
70 | $obj->share_from('main', $default_share); | |
71 | Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04); | |
72 | return $obj; | |
73 | } | |
74 | ||
75 | sub DESTROY { | |
76 | my $obj = shift; | |
77 | $obj->erase('DESTROY') if $obj->{Erase}; | |
78 | } | |
79 | ||
80 | sub erase { | |
81 | my ($obj, $action) = @_; | |
82 | my $pkg = $obj->root(); | |
83 | my ($stem, $leaf); | |
84 | ||
85 | no strict 'refs'; | |
86 | $pkg = "main::$pkg\::"; # expand to full symbol table name | |
87 | ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/; | |
88 | ||
89 | # The 'my $foo' is needed! Without it you get an | |
90 | # 'Attempt to free unreferenced scalar' warning! | |
91 | my $stem_symtab = *{$stem}{HASH}; | |
92 | ||
93 | #warn "erase($pkg) stem=$stem, leaf=$leaf"; | |
94 | #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n"; | |
95 | # ", join(', ', %$stem_symtab),"\n"; | |
96 | ||
97 | # delete $stem_symtab->{$leaf}; | |
98 | ||
99 | my $leaf_glob = $stem_symtab->{$leaf}; | |
100 | my $leaf_symtab = *{$leaf_glob}{HASH}; | |
101 | # warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n"; | |
102 | %$leaf_symtab = (); | |
103 | #delete $leaf_symtab->{'__ANON__'}; | |
104 | #delete $leaf_symtab->{'foo'}; | |
105 | #delete $leaf_symtab->{'main::'}; | |
106 | # my $foo = undef ${"$stem\::"}{"$leaf\::"}; | |
107 | ||
108 | if ($action and $action eq 'DESTROY') { | |
109 | delete $stem_symtab->{$leaf}; | |
110 | } else { | |
111 | $obj->share_from('main', $default_share); | |
112 | } | |
113 | 1; | |
114 | } | |
115 | ||
116 | ||
117 | sub reinit { | |
118 | my $obj= shift; | |
119 | $obj->erase; | |
120 | $obj->share_redo; | |
121 | } | |
122 | ||
123 | sub root { | |
124 | my $obj = shift; | |
125 | croak("Safe root method now read-only") if @_; | |
126 | return $obj->{Root}; | |
127 | } | |
128 | ||
129 | ||
130 | sub mask { | |
131 | my $obj = shift; | |
132 | return $obj->{Mask} unless @_; | |
133 | $obj->deny_only(@_); | |
134 | } | |
135 | ||
136 | # v1 compatibility methods | |
137 | sub trap { shift->deny(@_) } | |
138 | sub untrap { shift->permit(@_) } | |
139 | ||
140 | sub deny { | |
141 | my $obj = shift; | |
142 | $obj->{Mask} |= opset(@_); | |
143 | } | |
144 | sub deny_only { | |
145 | my $obj = shift; | |
146 | $obj->{Mask} = opset(@_); | |
147 | } | |
148 | ||
149 | sub permit { | |
150 | my $obj = shift; | |
151 | # XXX needs testing | |
152 | $obj->{Mask} &= invert_opset opset(@_); | |
153 | } | |
154 | sub permit_only { | |
155 | my $obj = shift; | |
156 | $obj->{Mask} = invert_opset opset(@_); | |
157 | } | |
158 | ||
159 | ||
160 | sub dump_mask { | |
161 | my $obj = shift; | |
162 | print opset_to_hex($obj->{Mask}),"\n"; | |
163 | } | |
164 | ||
165 | ||
166 | ||
167 | sub share { | |
168 | my($obj, @vars) = @_; | |
169 | $obj->share_from(scalar(caller), \@vars); | |
170 | } | |
171 | ||
172 | sub share_from { | |
173 | my $obj = shift; | |
174 | my $pkg = shift; | |
175 | my $vars = shift; | |
176 | my $no_record = shift || 0; | |
177 | my $root = $obj->root(); | |
178 | croak("vars not an array ref") unless ref $vars eq 'ARRAY'; | |
179 | no strict 'refs'; | |
180 | # Check that 'from' package actually exists | |
181 | croak("Package \"$pkg\" does not exist") | |
182 | unless keys %{"$pkg\::"}; | |
183 | my $arg; | |
184 | foreach $arg (@$vars) { | |
185 | # catch some $safe->share($var) errors: | |
186 | croak("'$arg' not a valid symbol table name") | |
187 | unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/ | |
188 | or $arg =~ /^\$\W$/; | |
189 | my ($var, $type); | |
190 | $type = $1 if ($var = $arg) =~ s/^(\W)//; | |
191 | # warn "share_from $pkg $type $var"; | |
192 | *{$root."::$var"} = (!$type) ? \&{$pkg."::$var"} | |
193 | : ($type eq '&') ? \&{$pkg."::$var"} | |
194 | : ($type eq '$') ? \${$pkg."::$var"} | |
195 | : ($type eq '@') ? \@{$pkg."::$var"} | |
196 | : ($type eq '%') ? \%{$pkg."::$var"} | |
197 | : ($type eq '*') ? *{$pkg."::$var"} | |
198 | : croak(qq(Can't share "$type$var" of unknown type)); | |
199 | } | |
200 | $obj->share_record($pkg, $vars) unless $no_record or !$vars; | |
201 | } | |
202 | ||
203 | sub share_record { | |
204 | my $obj = shift; | |
205 | my $pkg = shift; | |
206 | my $vars = shift; | |
207 | my $shares = \%{$obj->{Shares} ||= {}}; | |
208 | # Record shares using keys of $obj->{Shares}. See reinit. | |
209 | @{$shares}{@$vars} = ($pkg) x @$vars if @$vars; | |
210 | } | |
211 | sub share_redo { | |
212 | my $obj = shift; | |
213 | my $shares = \%{$obj->{Shares} ||= {}}; | |
214 | my($var, $pkg); | |
215 | while(($var, $pkg) = each %$shares) { | |
216 | # warn "share_redo $pkg\:: $var"; | |
217 | $obj->share_from($pkg, [ $var ], 1); | |
218 | } | |
219 | } | |
220 | sub share_forget { | |
221 | delete shift->{Shares}; | |
222 | } | |
223 | ||
224 | sub varglob { | |
225 | my ($obj, $var) = @_; | |
226 | no strict 'refs'; | |
227 | return *{$obj->root()."::$var"}; | |
228 | } | |
229 | ||
230 | ||
231 | sub reval { | |
232 | my ($obj, $expr, $strict) = @_; | |
233 | my $root = $obj->{Root}; | |
234 | ||
235 | my $evalsub = lexless_anon_sub($root,$strict, $expr); | |
236 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); | |
237 | } | |
238 | ||
239 | sub rdo { | |
240 | my ($obj, $file) = @_; | |
241 | my $root = $obj->{Root}; | |
242 | ||
243 | my $evalsub = eval | |
244 | sprintf('package %s; sub { @_ = (); do $file }', $root); | |
245 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); | |
246 | } | |
247 | ||
248 | ||
249 | 1; | |
250 | ||
251 | __END__ | |
252 | ||
253 | =head1 NAME | |
254 | ||
255 | Safe - Compile and execute code in restricted compartments | |
256 | ||
257 | =head1 SYNOPSIS | |
258 | ||
259 | use Safe; | |
260 | ||
261 | $compartment = new Safe; | |
262 | ||
263 | $compartment->permit(qw(time sort :browse)); | |
264 | ||
265 | $result = $compartment->reval($unsafe_code); | |
266 | ||
267 | =head1 DESCRIPTION | |
268 | ||
269 | The Safe extension module allows the creation of compartments | |
270 | in which perl code can be evaluated. Each compartment has | |
271 | ||
272 | =over 8 | |
273 | ||
274 | =item a new namespace | |
275 | ||
276 | The "root" of the namespace (i.e. "main::") is changed to a | |
277 | different package and code evaluated in the compartment cannot | |
278 | refer to variables outside this namespace, even with run-time | |
279 | glob lookups and other tricks. | |
280 | ||
281 | Code which is compiled outside the compartment can choose to place | |
282 | variables into (or I<share> variables with) the compartment's namespace | |
283 | and only that data will be visible to code evaluated in the | |
284 | compartment. | |
285 | ||
286 | By default, the only variables shared with compartments are the | |
287 | "underscore" variables $_ and @_ (and, technically, the less frequently | |
288 | used %_, the _ filehandle and so on). This is because otherwise perl | |
289 | operators which default to $_ will not work and neither will the | |
290 | assignment of arguments to @_ on subroutine entry. | |
291 | ||
292 | =item an operator mask | |
293 | ||
294 | Each compartment has an associated "operator mask". Recall that | |
295 | perl code is compiled into an internal format before execution. | |
296 | Evaluating perl code (e.g. via "eval" or "do 'file'") causes | |
297 | the code to be compiled into an internal format and then, | |
298 | provided there was no error in the compilation, executed. | |
299 | Code evaluated in a compartment compiles subject to the | |
300 | compartment's operator mask. Attempting to evaluate code in a | |
301 | compartment which contains a masked operator will cause the | |
302 | compilation to fail with an error. The code will not be executed. | |
303 | ||
304 | The default operator mask for a newly created compartment is | |
305 | the ':default' optag. | |
306 | ||
307 | It is important that you read the Opcode(3) module documentation | |
308 | for more information, especially for detailed definitions of opnames, | |
309 | optags and opsets. | |
310 | ||
311 | Since it is only at the compilation stage that the operator mask | |
312 | applies, controlled access to potentially unsafe operations can | |
313 | be achieved by having a handle to a wrapper subroutine (written | |
314 | outside the compartment) placed into the compartment. For example, | |
315 | ||
316 | $cpt = new Safe; | |
317 | sub wrapper { | |
318 | # vet arguments and perform potentially unsafe operations | |
319 | } | |
320 | $cpt->share('&wrapper'); | |
321 | ||
322 | =back | |
323 | ||
324 | ||
325 | =head1 WARNING | |
326 | ||
327 | The authors make B<no warranty>, implied or otherwise, about the | |
328 | suitability of this software for safety or security purposes. | |
329 | ||
330 | The authors shall not in any case be liable for special, incidental, | |
331 | consequential, indirect or other similar damages arising from the use | |
332 | of this software. | |
333 | ||
334 | Your mileage will vary. If in any doubt B<do not use it>. | |
335 | ||
336 | ||
337 | =head2 RECENT CHANGES | |
338 | ||
339 | The interface to the Safe module has changed quite dramatically since | |
340 | version 1 (as supplied with Perl5.002). Study these pages carefully if | |
341 | you have code written to use Safe version 1 because you will need to | |
342 | makes changes. | |
343 | ||
344 | ||
345 | =head2 Methods in class Safe | |
346 | ||
347 | To create a new compartment, use | |
348 | ||
349 | $cpt = new Safe; | |
350 | ||
351 | Optional argument is (NAMESPACE), where NAMESPACE is the root namespace | |
352 | to use for the compartment (defaults to "Safe::Root0", incremented for | |
353 | each new compartment). | |
354 | ||
355 | Note that version 1.00 of the Safe module supported a second optional | |
356 | parameter, MASK. That functionality has been withdrawn pending deeper | |
357 | consideration. Use the permit and deny methods described below. | |
358 | ||
359 | The following methods can then be used on the compartment | |
360 | object returned by the above constructor. The object argument | |
361 | is implicit in each case. | |
362 | ||
363 | ||
364 | =over 8 | |
365 | ||
366 | =item permit (OP, ...) | |
367 | ||
368 | Permit the listed operators to be used when compiling code in the | |
369 | compartment (in I<addition> to any operators already permitted). | |
370 | ||
371 | You can list opcodes by names, or use a tag name; see | |
372 | L<Opcode/"Predefined Opcode Tags">. | |
373 | ||
374 | =item permit_only (OP, ...) | |
375 | ||
376 | Permit I<only> the listed operators to be used when compiling code in | |
377 | the compartment (I<no> other operators are permitted). | |
378 | ||
379 | =item deny (OP, ...) | |
380 | ||
381 | Deny the listed operators from being used when compiling code in the | |
382 | compartment (other operators may still be permitted). | |
383 | ||
384 | =item deny_only (OP, ...) | |
385 | ||
386 | Deny I<only> the listed operators from being used when compiling code | |
387 | in the compartment (I<all> other operators will be permitted). | |
388 | ||
389 | =item trap (OP, ...) | |
390 | ||
391 | =item untrap (OP, ...) | |
392 | ||
393 | The trap and untrap methods are synonyms for deny and permit | |
394 | respectfully. | |
395 | ||
396 | =item share (NAME, ...) | |
397 | ||
398 | This shares the variable(s) in the argument list with the compartment. | |
399 | This is almost identical to exporting variables using the L<Exporter> | |
400 | module. | |
401 | ||
402 | Each NAME must be the B<name> of a non-lexical variable, typically | |
403 | with the leading type identifier included. A bareword is treated as a | |
404 | function name. | |
405 | ||
406 | Examples of legal names are '$foo' for a scalar, '@foo' for an | |
407 | array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo' | |
408 | for a glob (i.e. all symbol table entries associated with "foo", | |
409 | including scalar, array, hash, sub and filehandle). | |
410 | ||
411 | Each NAME is assumed to be in the calling package. See share_from | |
412 | for an alternative method (which share uses). | |
413 | ||
414 | =item share_from (PACKAGE, ARRAYREF) | |
415 | ||
416 | This method is similar to share() but allows you to explicitly name the | |
417 | package that symbols should be shared from. The symbol names (including | |
418 | type characters) are supplied as an array reference. | |
419 | ||
420 | $safe->share_from('main', [ '$foo', '%bar', 'func' ]); | |
421 | ||
422 | ||
423 | =item varglob (VARNAME) | |
424 | ||
425 | This returns a glob reference for the symbol table entry of VARNAME in | |
426 | the package of the compartment. VARNAME must be the B<name> of a | |
427 | variable without any leading type marker. For example, | |
428 | ||
429 | $cpt = new Safe 'Root'; | |
430 | $Root::foo = "Hello world"; | |
431 | # Equivalent version which doesn't need to know $cpt's package name: | |
432 | ${$cpt->varglob('foo')} = "Hello world"; | |
433 | ||
434 | ||
435 | =item reval (STRING) | |
436 | ||
437 | This evaluates STRING as perl code inside the compartment. | |
438 | ||
439 | The code can only see the compartment's namespace (as returned by the | |
440 | B<root> method). The compartment's root package appears to be the | |
441 | C<main::> package to the code inside the compartment. | |
442 | ||
443 | Any attempt by the code in STRING to use an operator which is not permitted | |
444 | by the compartment will cause an error (at run-time of the main program | |
445 | but at compile-time for the code in STRING). The error is of the form | |
446 | "'%s' trapped by operation mask...". | |
447 | ||
448 | If an operation is trapped in this way, then the code in STRING will | |
449 | not be executed. If such a trapped operation occurs or any other | |
450 | compile-time or return error, then $@ is set to the error message, just | |
451 | as with an eval(). | |
452 | ||
453 | If there is no error, then the method returns the value of the last | |
454 | expression evaluated, or a return statement may be used, just as with | |
455 | subroutines and B<eval()>. The context (list or scalar) is determined | |
456 | by the caller as usual. | |
457 | ||
458 | This behaviour differs from the beta distribution of the Safe extension | |
459 | where earlier versions of perl made it hard to mimic the return | |
460 | behaviour of the eval() command and the context was always scalar. | |
461 | ||
462 | Some points to note: | |
463 | ||
464 | If the entereval op is permitted then the code can use eval "..." to | |
465 | 'hide' code which might use denied ops. This is not a major problem | |
466 | since when the code tries to execute the eval it will fail because the | |
467 | opmask is still in effect. However this technique would allow clever, | |
468 | and possibly harmful, code to 'probe' the boundaries of what is | |
469 | possible. | |
470 | ||
471 | Any string eval which is executed by code executing in a compartment, | |
472 | or by code called from code executing in a compartment, will be eval'd | |
473 | in the namespace of the compartment. This is potentially a serious | |
474 | problem. | |
475 | ||
476 | Consider a function foo() in package pkg compiled outside a compartment | |
477 | but shared with it. Assume the compartment has a root package called | |
478 | 'Root'. If foo() contains an eval statement like eval '$foo = 1' then, | |
479 | normally, $pkg::foo will be set to 1. If foo() is called from the | |
480 | compartment (by whatever means) then instead of setting $pkg::foo, the | |
481 | eval will actually set $Root::pkg::foo. | |
482 | ||
483 | This can easily be demonstrated by using a module, such as the Socket | |
484 | module, which uses eval "..." as part of an AUTOLOAD function. You can | |
485 | 'use' the module outside the compartment and share an (autoloaded) | |
486 | function with the compartment. If an autoload is triggered by code in | |
487 | the compartment, or by any code anywhere that is called by any means | |
488 | from the compartment, then the eval in the Socket module's AUTOLOAD | |
489 | function happens in the namespace of the compartment. Any variables | |
490 | created or used by the eval'd code are now under the control of | |
491 | the code in the compartment. | |
492 | ||
493 | A similar effect applies to I<all> runtime symbol lookups in code | |
494 | called from a compartment but not compiled within it. | |
495 | ||
496 | ||
497 | ||
498 | =item rdo (FILENAME) | |
499 | ||
500 | This evaluates the contents of file FILENAME inside the compartment. | |
501 | See above documentation on the B<reval> method for further details. | |
502 | ||
503 | =item root (NAMESPACE) | |
504 | ||
505 | This method returns the name of the package that is the root of the | |
506 | compartment's namespace. | |
507 | ||
508 | Note that this behaviour differs from version 1.00 of the Safe module | |
509 | where the root module could be used to change the namespace. That | |
510 | functionality has been withdrawn pending deeper consideration. | |
511 | ||
512 | =item mask (MASK) | |
513 | ||
514 | This is a get-or-set method for the compartment's operator mask. | |
515 | ||
516 | With no MASK argument present, it returns the current operator mask of | |
517 | the compartment. | |
518 | ||
519 | With the MASK argument present, it sets the operator mask for the | |
520 | compartment (equivalent to calling the deny_only method). | |
521 | ||
522 | =back | |
523 | ||
524 | ||
525 | =head2 Some Safety Issues | |
526 | ||
527 | This section is currently just an outline of some of the things code in | |
528 | a compartment might do (intentionally or unintentionally) which can | |
529 | have an effect outside the compartment. | |
530 | ||
531 | =over 8 | |
532 | ||
533 | =item Memory | |
534 | ||
535 | Consuming all (or nearly all) available memory. | |
536 | ||
537 | =item CPU | |
538 | ||
539 | Causing infinite loops etc. | |
540 | ||
541 | =item Snooping | |
542 | ||
543 | Copying private information out of your system. Even something as | |
544 | simple as your user name is of value to others. Much useful information | |
545 | could be gleaned from your environment variables for example. | |
546 | ||
547 | =item Signals | |
548 | ||
549 | Causing signals (especially SIGFPE and SIGALARM) to affect your process. | |
550 | ||
551 | Setting up a signal handler will need to be carefully considered | |
552 | and controlled. What mask is in effect when a signal handler | |
553 | gets called? If a user can get an imported function to get an | |
554 | exception and call the user's signal handler, does that user's | |
555 | restricted mask get re-instated before the handler is called? | |
556 | Does an imported handler get called with its original mask or | |
557 | the user's one? | |
558 | ||
559 | =item State Changes | |
560 | ||
561 | Ops such as chdir obviously effect the process as a whole and not just | |
562 | the code in the compartment. Ops such as rand and srand have a similar | |
563 | but more subtle effect. | |
564 | ||
565 | =back | |
566 | ||
567 | =head2 AUTHOR | |
568 | ||
569 | Originally designed and implemented by Malcolm Beattie, | |
570 | mbeattie@sable.ox.ac.uk. | |
571 | ||
572 | Reworked to use the Opcode module and other changes added by Tim Bunce | |
573 | E<lt>F<Tim.Bunce@ig.co.uk>E<gt>. | |
574 | ||
575 | =cut | |
576 |