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1 | package Safe; |
2 | |
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3 | use 5.003_11; |
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4 | use strict; |
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5 | use vars qw($VERSION); |
6 | |
7 | $VERSION = "2.06"; |
8 | |
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9 | use Carp; |
10 | |
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11 | use Opcode 1.01, qw( |
12 | opset opset_to_ops opmask_add |
13 | empty_opset full_opset invert_opset verify_opset |
14 | opdesc opcodes opmask define_optag opset_to_hex |
15 | ); |
16 | |
17 | *ops_to_opset = \&opset; # Temporary alias for old Penguins |
18 | |
19 | |
20 | my $default_root = 0; |
21 | my $default_share = ['*_']; #, '*main::']; |
22 | |
23 | sub new { |
24 | my($class, $root, $mask) = @_; |
25 | my $obj = {}; |
26 | bless $obj, $class; |
27 | |
28 | if (defined($root)) { |
29 | croak "Can't use \"$root\" as root name" |
30 | if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/; |
31 | $obj->{Root} = $root; |
32 | $obj->{Erase} = 0; |
33 | } |
34 | else { |
35 | $obj->{Root} = "Safe::Root".$default_root++; |
36 | $obj->{Erase} = 1; |
37 | } |
38 | |
39 | # use permit/deny methods instead till interface issues resolved |
40 | # XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...; |
41 | croak "Mask parameter to new no longer supported" if defined $mask; |
42 | $obj->permit_only(':default'); |
43 | |
44 | # We must share $_ and @_ with the compartment or else ops such |
45 | # as split, length and so on won't default to $_ properly, nor |
46 | # will passing argument to subroutines work (via @_). In fact, |
47 | # for reasons I don't completely understand, we need to share |
48 | # the whole glob *_ rather than $_ and @_ separately, otherwise |
49 | # @_ in non default packages within the compartment don't work. |
50 | $obj->share_from('main', $default_share); |
51 | return $obj; |
52 | } |
53 | |
54 | sub DESTROY { |
55 | my $obj = shift; |
56 | $obj->erase if $obj->{Erase}; |
57 | } |
58 | |
59 | sub erase { |
60 | my $obj= shift; |
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 | $obj->share_from('main', $default_share); |
88 | 1; |
89 | } |
90 | |
91 | |
92 | sub reinit { |
93 | my $obj= shift; |
94 | $obj->erase; |
95 | $obj->share_redo; |
96 | } |
97 | |
98 | sub root { |
99 | my $obj = shift; |
100 | croak("Safe root method now read-only") if @_; |
101 | return $obj->{Root}; |
102 | } |
103 | |
104 | |
105 | sub mask { |
106 | my $obj = shift; |
107 | return $obj->{Mask} unless @_; |
108 | $obj->deny_only(@_); |
109 | } |
110 | |
111 | # v1 compatibility methods |
112 | sub trap { shift->deny(@_) } |
113 | sub untrap { shift->permit(@_) } |
114 | |
115 | sub deny { |
116 | my $obj = shift; |
117 | $obj->{Mask} |= opset(@_); |
118 | } |
119 | sub deny_only { |
120 | my $obj = shift; |
121 | $obj->{Mask} = opset(@_); |
122 | } |
123 | |
124 | sub permit { |
125 | my $obj = shift; |
126 | # XXX needs testing |
127 | $obj->{Mask} &= invert_opset opset(@_); |
128 | } |
129 | sub permit_only { |
130 | my $obj = shift; |
131 | $obj->{Mask} = invert_opset opset(@_); |
132 | } |
133 | |
134 | |
135 | sub dump_mask { |
136 | my $obj = shift; |
137 | print opset_to_hex($obj->{Mask}),"\n"; |
138 | } |
139 | |
140 | |
141 | |
142 | sub share { |
143 | my($obj, @vars) = @_; |
144 | $obj->share_from(scalar(caller), \@vars); |
145 | } |
146 | |
147 | sub share_from { |
148 | my $obj = shift; |
149 | my $pkg = shift; |
150 | my $vars = shift; |
151 | my $no_record = shift || 0; |
152 | my $root = $obj->root(); |
153 | my ($var, $arg); |
154 | croak("vars not an array ref") unless ref $vars eq 'ARRAY'; |
155 | no strict 'refs'; |
156 | # Check that 'from' package actually exists |
157 | croak("Package \"$pkg\" does not exist") |
158 | unless keys %{"$pkg\::"}; |
159 | foreach $arg (@$vars) { |
160 | # catch some $safe->share($var) errors: |
161 | croak("'$arg' not a valid symbol table name") |
162 | unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/ |
163 | or $arg =~ /^\$\W$/; |
164 | ($var = $arg) =~ s/^(\W)//; # get type char |
165 | # warn "share_from $pkg $1 $var"; |
166 | *{$root."::$var"} = ($1 eq '$') ? \${$pkg."::$var"} |
167 | : ($1 eq '@') ? \@{$pkg."::$var"} |
168 | : ($1 eq '%') ? \%{$pkg."::$var"} |
169 | : ($1 eq '*') ? *{$pkg."::$var"} |
170 | : ($1 eq '&') ? \&{$pkg."::$var"} |
171 | : (!$1) ? \&{$pkg."::$var"} |
172 | : croak(qq(Can't share "$1$var" of unknown type)); |
173 | } |
174 | $obj->share_record($pkg, $vars) unless $no_record or !$vars; |
175 | } |
176 | |
177 | sub share_record { |
178 | my $obj = shift; |
179 | my $pkg = shift; |
180 | my $vars = shift; |
181 | my $shares = \%{$obj->{Shares} ||= {}}; |
182 | # Record shares using keys of $obj->{Shares}. See reinit. |
183 | @{$shares}{@$vars} = ($pkg) x @$vars if @$vars; |
184 | } |
185 | sub share_redo { |
186 | my $obj = shift; |
187 | my $shares = \%{$obj->{Shares} ||= {}}; |
188 | my($var, $pkg); |
189 | while(($var, $pkg) = each %$shares) { |
190 | # warn "share_redo $pkg\:: $var"; |
191 | $obj->share_from($pkg, [ $var ], 1); |
192 | } |
193 | } |
194 | sub share_forget { |
195 | delete shift->{Shares}; |
196 | } |
197 | |
198 | sub varglob { |
199 | my ($obj, $var) = @_; |
200 | no strict 'refs'; |
201 | return *{$obj->root()."::$var"}; |
202 | } |
203 | |
204 | |
205 | sub reval { |
206 | my ($obj, $expr, $strict) = @_; |
207 | my $root = $obj->{Root}; |
208 | |
209 | # Create anon sub ref in root of compartment. |
210 | # Uses a closure (on $expr) to pass in the code to be executed. |
211 | # (eval on one line to keep line numbers as expected by caller) |
212 | my $evalcode = sprintf('package %s; sub { eval $expr; }', $root); |
213 | my $evalsub; |
214 | |
215 | if ($strict) { use strict; $evalsub = eval $evalcode; } |
216 | else { no strict; $evalsub = eval $evalcode; } |
217 | |
218 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
219 | } |
220 | |
221 | sub rdo { |
222 | my ($obj, $file) = @_; |
223 | my $root = $obj->{Root}; |
224 | |
225 | my $evalsub = eval |
226 | sprintf('package %s; sub { do $file }', $root); |
227 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
228 | } |
229 | |
230 | |
231 | 1; |
232 | |
233 | __DATA__ |
234 | |
235 | =head1 NAME |
236 | |
237 | Safe - Compile and execute code in restricted compartments |
238 | |
239 | =head1 SYNOPSIS |
240 | |
241 | use Safe; |
242 | |
243 | $compartment = new Safe; |
244 | |
245 | $compartment->permit(qw(time sort :browse)); |
246 | |
247 | $result = $compartment->reval($unsafe_code); |
248 | |
249 | =head1 DESCRIPTION |
250 | |
251 | The Safe extension module allows the creation of compartments |
252 | in which perl code can be evaluated. Each compartment has |
253 | |
254 | =over 8 |
255 | |
256 | =item a new namespace |
257 | |
258 | The "root" of the namespace (i.e. "main::") is changed to a |
259 | different package and code evaluated in the compartment cannot |
260 | refer to variables outside this namespace, even with run-time |
261 | glob lookups and other tricks. |
262 | |
263 | Code which is compiled outside the compartment can choose to place |
264 | variables into (or I<share> variables with) the compartment's namespace |
265 | and only that data will be visible to code evaluated in the |
266 | compartment. |
267 | |
268 | By default, the only variables shared with compartments are the |
269 | "underscore" variables $_ and @_ (and, technically, the less frequently |
270 | used %_, the _ filehandle and so on). This is because otherwise perl |
271 | operators which default to $_ will not work and neither will the |
272 | assignment of arguments to @_ on subroutine entry. |
273 | |
274 | =item an operator mask |
275 | |
276 | Each compartment has an associated "operator mask". Recall that |
277 | perl code is compiled into an internal format before execution. |
278 | Evaluating perl code (e.g. via "eval" or "do 'file'") causes |
279 | the code to be compiled into an internal format and then, |
280 | provided there was no error in the compilation, executed. |
281 | Code evaulated in a compartment compiles subject to the |
282 | compartment's operator mask. Attempting to evaulate code in a |
283 | compartment which contains a masked operator will cause the |
284 | compilation to fail with an error. The code will not be executed. |
285 | |
286 | The default operator mask for a newly created compartment is |
287 | the ':default' optag. |
288 | |
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289 | It is important that you read the Opcode(3) module documentation |
290 | for more information, especially for detailed definitions of opnames, |
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291 | optags and opsets. |
292 | |
293 | Since it is only at the compilation stage that the operator mask |
294 | applies, controlled access to potentially unsafe operations can |
295 | be achieved by having a handle to a wrapper subroutine (written |
296 | outside the compartment) placed into the compartment. For example, |
297 | |
298 | $cpt = new Safe; |
299 | sub wrapper { |
300 | # vet arguments and perform potentially unsafe operations |
301 | } |
302 | $cpt->share('&wrapper'); |
303 | |
304 | =back |
305 | |
306 | |
307 | =head1 WARNING |
308 | |
309 | The authors make B<no warranty>, implied or otherwise, about the |
310 | suitability of this software for safety or security purposes. |
311 | |
312 | The authors shall not in any case be liable for special, incidental, |
313 | consequential, indirect or other similar damages arising from the use |
314 | of this software. |
315 | |
316 | Your mileage will vary. If in any doubt B<do not use it>. |
317 | |
318 | |
319 | =head2 RECENT CHANGES |
320 | |
321 | The interface to the Safe module has changed quite dramatically since |
322 | version 1 (as supplied with Perl5.002). Study these pages carefully if |
323 | you have code written to use Safe version 1 because you will need to |
324 | makes changes. |
325 | |
326 | |
327 | =head2 Methods in class Safe |
328 | |
329 | To create a new compartment, use |
330 | |
331 | $cpt = new Safe; |
332 | |
333 | Optional argument is (NAMESPACE), where NAMESPACE is the root namespace |
334 | to use for the compartment (defaults to "Safe::Root0", incremented for |
335 | each new compartment). |
336 | |
337 | Note that version 1.00 of the Safe module supported a second optional |
338 | parameter, MASK. That functionality has been withdrawn pending deeper |
339 | consideration. Use the permit and deny methods described below. |
340 | |
341 | The following methods can then be used on the compartment |
342 | object returned by the above constructor. The object argument |
343 | is implicit in each case. |
344 | |
345 | |
346 | =over 8 |
347 | |
348 | =item permit (OP, ...) |
349 | |
350 | Permit the listed operators to be used when compiling code in the |
351 | compartment (in I<addition> to any operators already permitted). |
352 | |
353 | =item permit_only (OP, ...) |
354 | |
355 | Permit I<only> the listed operators to be used when compiling code in |
356 | the compartment (I<no> other operators are permitted). |
357 | |
358 | =item deny (OP, ...) |
359 | |
360 | Deny the listed operators from being used when compiling code in the |
361 | compartment (other operators may still be permitted). |
362 | |
363 | =item deny_only (OP, ...) |
364 | |
365 | Deny I<only> the listed operators from being used when compiling code |
366 | in the compartment (I<all> other operators will be permitted). |
367 | |
368 | =item trap (OP, ...) |
369 | |
370 | =item untrap (OP, ...) |
371 | |
372 | The trap and untrap methods are synonyms for deny and permit |
373 | respectfully. |
374 | |
375 | =item share (NAME, ...) |
376 | |
377 | This shares the variable(s) in the argument list with the compartment. |
378 | This is almost identical to exporting variables using the L<Exporter(3)> |
379 | module. |
380 | |
381 | Each NAME must be the B<name> of a variable, typically with the leading |
382 | type identifier included. A bareword is treated as a function name. |
383 | |
384 | Examples of legal names are '$foo' for a scalar, '@foo' for an |
385 | array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo' |
386 | for a glob (i.e. all symbol table entries associated with "foo", |
387 | including scalar, array, hash, sub and filehandle). |
388 | |
389 | Each NAME is assumed to be in the calling package. See share_from |
390 | for an alternative method (which share uses). |
391 | |
392 | =item share_from (PACKAGE, ARRAYREF) |
393 | |
394 | This method is similar to share() but allows you to explicitly name the |
395 | package that symbols should be shared from. The symbol names (including |
396 | type characters) are supplied as an array reference. |
397 | |
398 | $safe->share_from('main', [ '$foo', '%bar', 'func' ]); |
399 | |
400 | |
401 | =item varglob (VARNAME) |
402 | |
403 | This returns a glob reference for the symbol table entry of VARNAME in |
404 | the package of the compartment. VARNAME must be the B<name> of a |
405 | variable without any leading type marker. For example, |
406 | |
407 | $cpt = new Safe 'Root'; |
408 | $Root::foo = "Hello world"; |
409 | # Equivalent version which doesn't need to know $cpt's package name: |
410 | ${$cpt->varglob('foo')} = "Hello world"; |
411 | |
412 | |
413 | =item reval (STRING) |
414 | |
415 | This evaluates STRING as perl code inside the compartment. |
416 | |
417 | The code can only see the compartment's namespace (as returned by the |
418 | B<root> method). The compartment's root package appears to be the |
419 | C<main::> package to the code inside the compartment. |
420 | |
421 | Any attempt by the code in STRING to use an operator which is not permitted |
422 | by the compartment will cause an error (at run-time of the main program |
423 | but at compile-time for the code in STRING). The error is of the form |
424 | "%s trapped by operation mask operation...". |
425 | |
426 | If an operation is trapped in this way, then the code in STRING will |
427 | not be executed. If such a trapped operation occurs or any other |
428 | compile-time or return error, then $@ is set to the error message, just |
429 | as with an eval(). |
430 | |
431 | If there is no error, then the method returns the value of the last |
432 | expression evaluated, or a return statement may be used, just as with |
433 | subroutines and B<eval()>. The context (list or scalar) is determined |
434 | by the caller as usual. |
435 | |
436 | This behaviour differs from the beta distribution of the Safe extension |
437 | where earlier versions of perl made it hard to mimic the return |
438 | behaviour of the eval() command and the context was always scalar. |
439 | |
440 | Some points to note: |
441 | |
442 | If the entereval op is permitted then the code can use eval "..." to |
443 | 'hide' code which might use denied ops. This is not a major problem |
444 | since when the code tries to execute the eval it will fail because the |
445 | opmask is still in effect. However this technique would allow clever, |
446 | and possibly harmful, code to 'probe' the boundaries of what is |
447 | possible. |
448 | |
449 | Any string eval which is executed by code executing in a compartment, |
450 | or by code called from code executing in a compartment, will be eval'd |
451 | in the namespace of the compartment. This is potentially a serious |
452 | problem. |
453 | |
454 | Consider a function foo() in package pkg compiled outside a compartment |
455 | but shared with it. Assume the compartment has a root package called |
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456 | 'Root'. If foo() contains an eval statement like eval '$foo = 1' then, |
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457 | normally, $pkg::foo will be set to 1. If foo() is called from the |
458 | compartment (by whatever means) then instead of setting $pkg::foo, the |
459 | eval will actually set $Root::pkg::foo. |
460 | |
461 | This can easily be demonstrated by using a module, such as the Socket |
462 | module, which uses eval "..." as part of an AUTOLOAD function. You can |
463 | 'use' the module outside the compartment and share an (autoloaded) |
464 | function with the compartment. If an autoload is triggered by code in |
465 | the compartment, or by any code anywhere that is called by any means |
466 | from the compartment, then the eval in the Socket module's AUTOLOAD |
467 | function happens in the namespace of the compartment. Any variables |
468 | created or used by the eval'd code are now under the control of |
469 | the code in the compartment. |
470 | |
471 | A similar effect applies to I<all> runtime symbol lookups in code |
472 | called from a compartment but not compiled within it. |
473 | |
474 | |
475 | |
476 | =item rdo (FILENAME) |
477 | |
478 | This evaluates the contents of file FILENAME inside the compartment. |
479 | See above documentation on the B<reval> method for further details. |
480 | |
481 | =item root (NAMESPACE) |
482 | |
483 | This method returns the name of the package that is the root of the |
484 | compartment's namespace. |
485 | |
486 | Note that this behaviour differs from version 1.00 of the Safe module |
487 | where the root module could be used to change the namespace. That |
488 | functionality has been withdrawn pending deeper consideration. |
489 | |
490 | =item mask (MASK) |
491 | |
492 | This is a get-or-set method for the compartment's operator mask. |
493 | |
494 | With no MASK argument present, it returns the current operator mask of |
495 | the compartment. |
496 | |
497 | With the MASK argument present, it sets the operator mask for the |
498 | compartment (equivalent to calling the deny_only method). |
499 | |
500 | =back |
501 | |
502 | |
503 | =head2 Some Safety Issues |
504 | |
505 | This section is currently just an outline of some of the things code in |
506 | a compartment might do (intentionally or unintentionally) which can |
507 | have an effect outside the compartment. |
508 | |
509 | =over 8 |
510 | |
511 | =item Memory |
512 | |
513 | Consuming all (or nearly all) available memory. |
514 | |
515 | =item CPU |
516 | |
517 | Causing infinite loops etc. |
518 | |
519 | =item Snooping |
520 | |
521 | Copying private information out of your system. Even something as |
522 | simple as your user name is of value to others. Much useful information |
523 | could be gleaned from your environment variables for example. |
524 | |
525 | =item Signals |
526 | |
527 | Causing signals (especially SIGFPE and SIGALARM) to affect your process. |
528 | |
529 | Setting up a signal handler will need to be carefully considered |
530 | and controlled. What mask is in effect when a signal handler |
531 | gets called? If a user can get an imported function to get an |
532 | exception and call the user's signal handler, does that user's |
533 | restricted mask get re-instated before the handler is called? |
534 | Does an imported handler get called with its original mask or |
535 | the user's one? |
536 | |
537 | =item State Changes |
538 | |
539 | Ops such as chdir obviously effect the process as a whole and not just |
540 | the code in the compartment. Ops such as rand and srand have a similar |
541 | but more subtle effect. |
542 | |
543 | =back |
544 | |
545 | =head2 AUTHOR |
546 | |
547 | Originally designed and implemented by Malcolm Beattie, |
548 | mbeattie@sable.ox.ac.uk. |
549 | |
550 | Reworked to use the Opcode module and other changes added by Tim Bunce |
1fef88e7 |
551 | E<lt>F<Tim.Bunce@ig.co.uk>E<gt>. |
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552 | |
553 | =cut |
554 | |