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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 | |
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6 | our $VERSION = "2.06"; |
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7 | |
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8 | use Carp; |
9 | |
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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); |
50 | return $obj; |
51 | } |
52 | |
53 | sub DESTROY { |
54 | my $obj = shift; |
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55 | $obj->erase('DESTROY') if $obj->{Erase}; |
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56 | } |
57 | |
58 | sub erase { |
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59 | my ($obj, $action) = @_; |
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60 | my $pkg = $obj->root(); |
61 | my ($stem, $leaf); |
62 | |
63 | no strict 'refs'; |
64 | $pkg = "main::$pkg\::"; # expand to full symbol table name |
65 | ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/; |
66 | |
67 | # The 'my $foo' is needed! Without it you get an |
68 | # 'Attempt to free unreferenced scalar' warning! |
69 | my $stem_symtab = *{$stem}{HASH}; |
70 | |
71 | #warn "erase($pkg) stem=$stem, leaf=$leaf"; |
72 | #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n"; |
73 | # ", join(', ', %$stem_symtab),"\n"; |
74 | |
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75 | # delete $stem_symtab->{$leaf}; |
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76 | |
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77 | my $leaf_glob = $stem_symtab->{$leaf}; |
78 | my $leaf_symtab = *{$leaf_glob}{HASH}; |
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79 | # warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n"; |
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80 | %$leaf_symtab = (); |
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81 | #delete $leaf_symtab->{'__ANON__'}; |
82 | #delete $leaf_symtab->{'foo'}; |
83 | #delete $leaf_symtab->{'main::'}; |
84 | # my $foo = undef ${"$stem\::"}{"$leaf\::"}; |
85 | |
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86 | if ($action and $action eq 'DESTROY') { |
87 | delete $stem_symtab->{$leaf}; |
88 | } else { |
89 | $obj->share_from('main', $default_share); |
90 | } |
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91 | 1; |
92 | } |
93 | |
94 | |
95 | sub reinit { |
96 | my $obj= shift; |
97 | $obj->erase; |
98 | $obj->share_redo; |
99 | } |
100 | |
101 | sub root { |
102 | my $obj = shift; |
103 | croak("Safe root method now read-only") if @_; |
104 | return $obj->{Root}; |
105 | } |
106 | |
107 | |
108 | sub mask { |
109 | my $obj = shift; |
110 | return $obj->{Mask} unless @_; |
111 | $obj->deny_only(@_); |
112 | } |
113 | |
114 | # v1 compatibility methods |
115 | sub trap { shift->deny(@_) } |
116 | sub untrap { shift->permit(@_) } |
117 | |
118 | sub deny { |
119 | my $obj = shift; |
120 | $obj->{Mask} |= opset(@_); |
121 | } |
122 | sub deny_only { |
123 | my $obj = shift; |
124 | $obj->{Mask} = opset(@_); |
125 | } |
126 | |
127 | sub permit { |
128 | my $obj = shift; |
129 | # XXX needs testing |
130 | $obj->{Mask} &= invert_opset opset(@_); |
131 | } |
132 | sub permit_only { |
133 | my $obj = shift; |
134 | $obj->{Mask} = invert_opset opset(@_); |
135 | } |
136 | |
137 | |
138 | sub dump_mask { |
139 | my $obj = shift; |
140 | print opset_to_hex($obj->{Mask}),"\n"; |
141 | } |
142 | |
143 | |
144 | |
145 | sub share { |
146 | my($obj, @vars) = @_; |
147 | $obj->share_from(scalar(caller), \@vars); |
148 | } |
149 | |
150 | sub share_from { |
151 | my $obj = shift; |
152 | my $pkg = shift; |
153 | my $vars = shift; |
154 | my $no_record = shift || 0; |
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155 | my $root = $obj->root(); |
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156 | croak("vars not an array ref") unless ref $vars eq 'ARRAY'; |
157 | no strict 'refs'; |
158 | # Check that 'from' package actually exists |
159 | croak("Package \"$pkg\" does not exist") |
160 | unless keys %{"$pkg\::"}; |
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161 | my $arg; |
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162 | foreach $arg (@$vars) { |
163 | # catch some $safe->share($var) errors: |
164 | croak("'$arg' not a valid symbol table name") |
165 | unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/ |
166 | or $arg =~ /^\$\W$/; |
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167 | my ($var, $type); |
168 | $type = $1 if ($var = $arg) =~ s/^(\W)//; |
169 | # warn "share_from $pkg $type $var"; |
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170 | *{$root."::$var"} = (!$type) ? \&{$pkg."::$var"} |
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171 | : ($type eq '&') ? \&{$pkg."::$var"} |
172 | : ($type eq '$') ? \${$pkg."::$var"} |
173 | : ($type eq '@') ? \@{$pkg."::$var"} |
174 | : ($type eq '%') ? \%{$pkg."::$var"} |
175 | : ($type eq '*') ? *{$pkg."::$var"} |
176 | : croak(qq(Can't share "$type$var" of unknown type)); |
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177 | } |
178 | $obj->share_record($pkg, $vars) unless $no_record or !$vars; |
179 | } |
180 | |
181 | sub share_record { |
182 | my $obj = shift; |
183 | my $pkg = shift; |
184 | my $vars = shift; |
185 | my $shares = \%{$obj->{Shares} ||= {}}; |
186 | # Record shares using keys of $obj->{Shares}. See reinit. |
187 | @{$shares}{@$vars} = ($pkg) x @$vars if @$vars; |
188 | } |
189 | sub share_redo { |
190 | my $obj = shift; |
191 | my $shares = \%{$obj->{Shares} ||= {}}; |
192 | my($var, $pkg); |
193 | while(($var, $pkg) = each %$shares) { |
194 | # warn "share_redo $pkg\:: $var"; |
195 | $obj->share_from($pkg, [ $var ], 1); |
196 | } |
197 | } |
198 | sub share_forget { |
199 | delete shift->{Shares}; |
200 | } |
201 | |
202 | sub varglob { |
203 | my ($obj, $var) = @_; |
204 | no strict 'refs'; |
205 | return *{$obj->root()."::$var"}; |
206 | } |
207 | |
208 | |
209 | sub reval { |
210 | my ($obj, $expr, $strict) = @_; |
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211 | my $root = $obj->{Root}; |
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212 | |
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213 | # Create anon sub ref in root of compartment. |
214 | # Uses a closure (on $expr) to pass in the code to be executed. |
215 | # (eval on one line to keep line numbers as expected by caller) |
216 | my $evalcode = sprintf('package %s; sub { eval $expr; }', $root); |
217 | my $evalsub; |
218 | |
219 | if ($strict) { use strict; $evalsub = eval $evalcode; } |
220 | else { no strict; $evalsub = eval $evalcode; } |
221 | |
222 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
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223 | } |
224 | |
225 | sub rdo { |
226 | my ($obj, $file) = @_; |
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227 | my $root = $obj->{Root}; |
228 | |
229 | my $evalsub = eval |
230 | sprintf('package %s; sub { do $file }', $root); |
231 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
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232 | } |
233 | |
234 | |
235 | 1; |
236 | |
3e92a254 |
237 | __END__ |
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238 | |
239 | =head1 NAME |
240 | |
241 | Safe - Compile and execute code in restricted compartments |
242 | |
243 | =head1 SYNOPSIS |
244 | |
245 | use Safe; |
246 | |
247 | $compartment = new Safe; |
248 | |
249 | $compartment->permit(qw(time sort :browse)); |
250 | |
251 | $result = $compartment->reval($unsafe_code); |
252 | |
253 | =head1 DESCRIPTION |
254 | |
255 | The Safe extension module allows the creation of compartments |
256 | in which perl code can be evaluated. Each compartment has |
257 | |
258 | =over 8 |
259 | |
260 | =item a new namespace |
261 | |
262 | The "root" of the namespace (i.e. "main::") is changed to a |
263 | different package and code evaluated in the compartment cannot |
264 | refer to variables outside this namespace, even with run-time |
265 | glob lookups and other tricks. |
266 | |
267 | Code which is compiled outside the compartment can choose to place |
268 | variables into (or I<share> variables with) the compartment's namespace |
269 | and only that data will be visible to code evaluated in the |
270 | compartment. |
271 | |
272 | By default, the only variables shared with compartments are the |
273 | "underscore" variables $_ and @_ (and, technically, the less frequently |
274 | used %_, the _ filehandle and so on). This is because otherwise perl |
275 | operators which default to $_ will not work and neither will the |
276 | assignment of arguments to @_ on subroutine entry. |
277 | |
278 | =item an operator mask |
279 | |
280 | Each compartment has an associated "operator mask". Recall that |
281 | perl code is compiled into an internal format before execution. |
282 | Evaluating perl code (e.g. via "eval" or "do 'file'") causes |
283 | the code to be compiled into an internal format and then, |
284 | provided there was no error in the compilation, executed. |
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285 | Code evaluated in a compartment compiles subject to the |
286 | compartment's operator mask. Attempting to evaluate code in a |
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287 | compartment which contains a masked operator will cause the |
288 | compilation to fail with an error. The code will not be executed. |
289 | |
290 | The default operator mask for a newly created compartment is |
291 | the ':default' optag. |
292 | |
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293 | It is important that you read the Opcode(3) module documentation |
294 | for more information, especially for detailed definitions of opnames, |
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295 | optags and opsets. |
296 | |
297 | Since it is only at the compilation stage that the operator mask |
298 | applies, controlled access to potentially unsafe operations can |
299 | be achieved by having a handle to a wrapper subroutine (written |
300 | outside the compartment) placed into the compartment. For example, |
301 | |
302 | $cpt = new Safe; |
303 | sub wrapper { |
304 | # vet arguments and perform potentially unsafe operations |
305 | } |
306 | $cpt->share('&wrapper'); |
307 | |
308 | =back |
309 | |
310 | |
311 | =head1 WARNING |
312 | |
313 | The authors make B<no warranty>, implied or otherwise, about the |
314 | suitability of this software for safety or security purposes. |
315 | |
316 | The authors shall not in any case be liable for special, incidental, |
317 | consequential, indirect or other similar damages arising from the use |
318 | of this software. |
319 | |
320 | Your mileage will vary. If in any doubt B<do not use it>. |
321 | |
322 | |
323 | =head2 RECENT CHANGES |
324 | |
325 | The interface to the Safe module has changed quite dramatically since |
326 | version 1 (as supplied with Perl5.002). Study these pages carefully if |
327 | you have code written to use Safe version 1 because you will need to |
328 | makes changes. |
329 | |
330 | |
331 | =head2 Methods in class Safe |
332 | |
333 | To create a new compartment, use |
334 | |
335 | $cpt = new Safe; |
336 | |
337 | Optional argument is (NAMESPACE), where NAMESPACE is the root namespace |
338 | to use for the compartment (defaults to "Safe::Root0", incremented for |
339 | each new compartment). |
340 | |
341 | Note that version 1.00 of the Safe module supported a second optional |
342 | parameter, MASK. That functionality has been withdrawn pending deeper |
343 | consideration. Use the permit and deny methods described below. |
344 | |
345 | The following methods can then be used on the compartment |
346 | object returned by the above constructor. The object argument |
347 | is implicit in each case. |
348 | |
349 | |
350 | =over 8 |
351 | |
352 | =item permit (OP, ...) |
353 | |
354 | Permit the listed operators to be used when compiling code in the |
355 | compartment (in I<addition> to any operators already permitted). |
356 | |
357 | =item permit_only (OP, ...) |
358 | |
359 | Permit I<only> the listed operators to be used when compiling code in |
360 | the compartment (I<no> other operators are permitted). |
361 | |
362 | =item deny (OP, ...) |
363 | |
364 | Deny the listed operators from being used when compiling code in the |
365 | compartment (other operators may still be permitted). |
366 | |
367 | =item deny_only (OP, ...) |
368 | |
369 | Deny I<only> the listed operators from being used when compiling code |
370 | in the compartment (I<all> other operators will be permitted). |
371 | |
372 | =item trap (OP, ...) |
373 | |
374 | =item untrap (OP, ...) |
375 | |
376 | The trap and untrap methods are synonyms for deny and permit |
377 | respectfully. |
378 | |
379 | =item share (NAME, ...) |
380 | |
381 | This shares the variable(s) in the argument list with the compartment. |
382 | This is almost identical to exporting variables using the L<Exporter(3)> |
383 | module. |
384 | |
385 | Each NAME must be the B<name> of a variable, typically with the leading |
386 | type identifier included. A bareword is treated as a function name. |
387 | |
388 | Examples of legal names are '$foo' for a scalar, '@foo' for an |
389 | array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo' |
390 | for a glob (i.e. all symbol table entries associated with "foo", |
391 | including scalar, array, hash, sub and filehandle). |
392 | |
393 | Each NAME is assumed to be in the calling package. See share_from |
394 | for an alternative method (which share uses). |
395 | |
396 | =item share_from (PACKAGE, ARRAYREF) |
397 | |
398 | This method is similar to share() but allows you to explicitly name the |
399 | package that symbols should be shared from. The symbol names (including |
400 | type characters) are supplied as an array reference. |
401 | |
402 | $safe->share_from('main', [ '$foo', '%bar', 'func' ]); |
403 | |
404 | |
405 | =item varglob (VARNAME) |
406 | |
407 | This returns a glob reference for the symbol table entry of VARNAME in |
408 | the package of the compartment. VARNAME must be the B<name> of a |
409 | variable without any leading type marker. For example, |
410 | |
411 | $cpt = new Safe 'Root'; |
412 | $Root::foo = "Hello world"; |
413 | # Equivalent version which doesn't need to know $cpt's package name: |
414 | ${$cpt->varglob('foo')} = "Hello world"; |
415 | |
416 | |
417 | =item reval (STRING) |
418 | |
419 | This evaluates STRING as perl code inside the compartment. |
420 | |
421 | The code can only see the compartment's namespace (as returned by the |
422 | B<root> method). The compartment's root package appears to be the |
423 | C<main::> package to the code inside the compartment. |
424 | |
425 | Any attempt by the code in STRING to use an operator which is not permitted |
426 | by the compartment will cause an error (at run-time of the main program |
427 | but at compile-time for the code in STRING). The error is of the form |
428 | "%s trapped by operation mask operation...". |
429 | |
430 | If an operation is trapped in this way, then the code in STRING will |
431 | not be executed. If such a trapped operation occurs or any other |
432 | compile-time or return error, then $@ is set to the error message, just |
433 | as with an eval(). |
434 | |
435 | If there is no error, then the method returns the value of the last |
436 | expression evaluated, or a return statement may be used, just as with |
437 | subroutines and B<eval()>. The context (list or scalar) is determined |
438 | by the caller as usual. |
439 | |
440 | This behaviour differs from the beta distribution of the Safe extension |
441 | where earlier versions of perl made it hard to mimic the return |
442 | behaviour of the eval() command and the context was always scalar. |
443 | |
444 | Some points to note: |
445 | |
446 | If the entereval op is permitted then the code can use eval "..." to |
447 | 'hide' code which might use denied ops. This is not a major problem |
448 | since when the code tries to execute the eval it will fail because the |
449 | opmask is still in effect. However this technique would allow clever, |
450 | and possibly harmful, code to 'probe' the boundaries of what is |
451 | possible. |
452 | |
453 | Any string eval which is executed by code executing in a compartment, |
454 | or by code called from code executing in a compartment, will be eval'd |
455 | in the namespace of the compartment. This is potentially a serious |
456 | problem. |
457 | |
458 | Consider a function foo() in package pkg compiled outside a compartment |
459 | but shared with it. Assume the compartment has a root package called |
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460 | 'Root'. If foo() contains an eval statement like eval '$foo = 1' then, |
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461 | normally, $pkg::foo will be set to 1. If foo() is called from the |
462 | compartment (by whatever means) then instead of setting $pkg::foo, the |
463 | eval will actually set $Root::pkg::foo. |
464 | |
465 | This can easily be demonstrated by using a module, such as the Socket |
466 | module, which uses eval "..." as part of an AUTOLOAD function. You can |
467 | 'use' the module outside the compartment and share an (autoloaded) |
468 | function with the compartment. If an autoload is triggered by code in |
469 | the compartment, or by any code anywhere that is called by any means |
470 | from the compartment, then the eval in the Socket module's AUTOLOAD |
471 | function happens in the namespace of the compartment. Any variables |
472 | created or used by the eval'd code are now under the control of |
473 | the code in the compartment. |
474 | |
475 | A similar effect applies to I<all> runtime symbol lookups in code |
476 | called from a compartment but not compiled within it. |
477 | |
478 | |
479 | |
480 | =item rdo (FILENAME) |
481 | |
482 | This evaluates the contents of file FILENAME inside the compartment. |
483 | See above documentation on the B<reval> method for further details. |
484 | |
485 | =item root (NAMESPACE) |
486 | |
487 | This method returns the name of the package that is the root of the |
488 | compartment's namespace. |
489 | |
490 | Note that this behaviour differs from version 1.00 of the Safe module |
491 | where the root module could be used to change the namespace. That |
492 | functionality has been withdrawn pending deeper consideration. |
493 | |
494 | =item mask (MASK) |
495 | |
496 | This is a get-or-set method for the compartment's operator mask. |
497 | |
498 | With no MASK argument present, it returns the current operator mask of |
499 | the compartment. |
500 | |
501 | With the MASK argument present, it sets the operator mask for the |
502 | compartment (equivalent to calling the deny_only method). |
503 | |
504 | =back |
505 | |
506 | |
507 | =head2 Some Safety Issues |
508 | |
509 | This section is currently just an outline of some of the things code in |
510 | a compartment might do (intentionally or unintentionally) which can |
511 | have an effect outside the compartment. |
512 | |
513 | =over 8 |
514 | |
515 | =item Memory |
516 | |
517 | Consuming all (or nearly all) available memory. |
518 | |
519 | =item CPU |
520 | |
521 | Causing infinite loops etc. |
522 | |
523 | =item Snooping |
524 | |
525 | Copying private information out of your system. Even something as |
526 | simple as your user name is of value to others. Much useful information |
527 | could be gleaned from your environment variables for example. |
528 | |
529 | =item Signals |
530 | |
531 | Causing signals (especially SIGFPE and SIGALARM) to affect your process. |
532 | |
533 | Setting up a signal handler will need to be carefully considered |
534 | and controlled. What mask is in effect when a signal handler |
535 | gets called? If a user can get an imported function to get an |
536 | exception and call the user's signal handler, does that user's |
537 | restricted mask get re-instated before the handler is called? |
538 | Does an imported handler get called with its original mask or |
539 | the user's one? |
540 | |
541 | =item State Changes |
542 | |
543 | Ops such as chdir obviously effect the process as a whole and not just |
544 | the code in the compartment. Ops such as rand and srand have a similar |
545 | but more subtle effect. |
546 | |
547 | =back |
548 | |
549 | =head2 AUTHOR |
550 | |
551 | Originally designed and implemented by Malcolm Beattie, |
552 | mbeattie@sable.ox.ac.uk. |
553 | |
554 | Reworked to use the Opcode module and other changes added by Tim Bunce |
1fef88e7 |
555 | E<lt>F<Tim.Bunce@ig.co.uk>E<gt>. |
2ded1cc1 |
556 | |
557 | =cut |
558 | |