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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 | $Safe::VERSION = "2.12"; |
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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 | |
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 | } |
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27 | |
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28 | use Carp; |
b27d3831 |
29 | use Carp::Heavy; |
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30 | |
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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', $default_share); |
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71 | Opcode::_safe_pkg_prep($obj->{Root}) if($Opcode::VERSION > 1.04); |
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72 | return $obj; |
73 | } |
74 | |
75 | sub DESTROY { |
76 | my $obj = shift; |
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77 | $obj->erase('DESTROY') if $obj->{Erase}; |
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78 | } |
79 | |
80 | sub erase { |
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81 | my ($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 | |
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97 | # delete $stem_symtab->{$leaf}; |
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98 | |
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99 | my $leaf_glob = $stem_symtab->{$leaf}; |
100 | my $leaf_symtab = *{$leaf_glob}{HASH}; |
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101 | # warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n"; |
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102 | %$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 | |
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; |
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177 | my $root = $obj->root(); |
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178 | croak("vars not an array ref") unless ref $vars eq 'ARRAY'; |
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179 | no strict 'refs'; |
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180 | # Check that 'from' package actually exists |
181 | croak("Package \"$pkg\" does not exist") |
182 | unless keys %{"$pkg\::"}; |
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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 $var"; |
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192 | *{$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 | |
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} ||= {}}; |
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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, [ $var ], 1); |
218 | } |
219 | } |
220 | sub share_forget { |
221 | delete shift->{Shares}; |
222 | } |
223 | |
224 | sub varglob { |
225 | my ($obj, $var) = @_; |
226 | no strict 'refs'; |
227 | return *{$obj->root()."::$var"}; |
228 | } |
229 | |
230 | |
231 | sub reval { |
232 | my ($obj, $expr, $strict) = @_; |
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233 | my $root = $obj->{Root}; |
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234 | |
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235 | my $evalsub = lexless_anon_sub($root,$strict, $expr); |
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236 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
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237 | } |
238 | |
239 | sub rdo { |
240 | my ($obj, $file) = @_; |
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241 | my $root = $obj->{Root}; |
242 | |
243 | my $evalsub = eval |
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244 | sprintf('package %s; sub { @_ = (); do $file }', $root); |
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245 | return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub); |
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246 | } |
247 | |
248 | |
249 | 1; |
250 | |
3e92a254 |
251 | __END__ |
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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. |
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299 | Code evaluated in a compartment compiles subject to the |
300 | compartment's operator mask. Attempting to evaluate code in a |
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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 | |
86780939 |
307 | It is important that you read the L<Opcode> module documentation |
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308 | for more information, especially for detailed definitions of opnames, |
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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 | |
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371 | You can list opcodes by names, or use a tag name; see |
372 | L<Opcode/"Predefined Opcode Tags">. |
373 | |
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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. |
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399 | This is almost identical to exporting variables using the L<Exporter> |
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400 | module. |
401 | |
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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. |
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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 |
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446 | "'%s' trapped by operation mask...". |
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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 $@ is set to the error message, just |
451 | as with an eval(). |
452 | |
453 | If there is no error, then the method returns the value of the last |
454 | expression evaluated, or a return statement may be used, just as with |
455 | subroutines and B<eval()>. The context (list or scalar) is determined |
456 | by the caller as usual. |
457 | |
458 | This behaviour differs from the beta distribution of the Safe extension |
459 | where earlier versions of perl made it hard to mimic the return |
460 | behaviour of the eval() command and the context was always scalar. |
461 | |
462 | Some points to note: |
463 | |
464 | If the entereval op is permitted then the code can use eval "..." to |
465 | 'hide' code which might use denied ops. This is not a major problem |
466 | since when the code tries to execute the eval it will fail because the |
467 | opmask is still in effect. However this technique would allow clever, |
468 | and possibly harmful, code to 'probe' the boundaries of what is |
469 | possible. |
470 | |
471 | Any string eval which is executed by code executing in a compartment, |
472 | or by code called from code executing in a compartment, will be eval'd |
473 | in the namespace of the compartment. This is potentially a serious |
474 | problem. |
475 | |
476 | Consider a function foo() in package pkg compiled outside a compartment |
477 | but shared with it. Assume the compartment has a root package called |
1fef88e7 |
478 | 'Root'. If foo() contains an eval statement like eval '$foo = 1' then, |
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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 |
1fef88e7 |
573 | E<lt>F<Tim.Bunce@ig.co.uk>E<gt>. |
2ded1cc1 |
574 | |
575 | =cut |
576 | |