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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Safe 3" | |
132 | .TH Safe 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | Safe \- Compile and execute code in restricted compartments | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 1 | |
138 | \& use Safe; | |
139 | .Ve | |
140 | .PP | |
141 | .Vb 1 | |
142 | \& $compartment = new Safe; | |
143 | .Ve | |
144 | .PP | |
145 | .Vb 1 | |
146 | \& $compartment->permit(qw(time sort :browse)); | |
147 | .Ve | |
148 | .PP | |
149 | .Vb 1 | |
150 | \& $result = $compartment->reval($unsafe_code); | |
151 | .Ve | |
152 | .SH "DESCRIPTION" | |
153 | .IX Header "DESCRIPTION" | |
154 | The Safe extension module allows the creation of compartments | |
155 | in which perl code can be evaluated. Each compartment has | |
156 | .IP "a new namespace" 8 | |
157 | .IX Item "a new namespace" | |
158 | The \*(L"root\*(R" of the namespace (i.e. \*(L"main::\*(R") is changed to a | |
159 | different package and code evaluated in the compartment cannot | |
160 | refer to variables outside this namespace, even with run-time | |
161 | glob lookups and other tricks. | |
162 | .Sp | |
163 | Code which is compiled outside the compartment can choose to place | |
164 | variables into (or \fIshare\fR variables with) the compartment's namespace | |
165 | and only that data will be visible to code evaluated in the | |
166 | compartment. | |
167 | .Sp | |
168 | By default, the only variables shared with compartments are the | |
169 | \&\*(L"underscore\*(R" variables \f(CW$_\fR and \f(CW@_\fR (and, technically, the less frequently | |
170 | used \f(CW%_\fR, the _ filehandle and so on). This is because otherwise perl | |
171 | operators which default to \f(CW$_\fR will not work and neither will the | |
172 | assignment of arguments to \f(CW@_\fR on subroutine entry. | |
173 | .IP "an operator mask" 8 | |
174 | .IX Item "an operator mask" | |
175 | Each compartment has an associated \*(L"operator mask\*(R". Recall that | |
176 | perl code is compiled into an internal format before execution. | |
177 | Evaluating perl code (e.g. via \*(L"eval\*(R" or \*(L"do 'file'\*(R") causes | |
178 | the code to be compiled into an internal format and then, | |
179 | provided there was no error in the compilation, executed. | |
180 | Code evaluated in a compartment compiles subject to the | |
181 | compartment's operator mask. Attempting to evaluate code in a | |
182 | compartment which contains a masked operator will cause the | |
183 | compilation to fail with an error. The code will not be executed. | |
184 | .Sp | |
185 | The default operator mask for a newly created compartment is | |
186 | the ':default' optag. | |
187 | .Sp | |
188 | It is important that you read the \fIOpcode\fR\|(3) module documentation | |
189 | for more information, especially for detailed definitions of opnames, | |
190 | optags and opsets. | |
191 | .Sp | |
192 | Since it is only at the compilation stage that the operator mask | |
193 | applies, controlled access to potentially unsafe operations can | |
194 | be achieved by having a handle to a wrapper subroutine (written | |
195 | outside the compartment) placed into the compartment. For example, | |
196 | .Sp | |
197 | .Vb 5 | |
198 | \& $cpt = new Safe; | |
199 | \& sub wrapper { | |
200 | \& # vet arguments and perform potentially unsafe operations | |
201 | \& } | |
202 | \& $cpt->share('&wrapper'); | |
203 | .Ve | |
204 | .SH "WARNING" | |
205 | .IX Header "WARNING" | |
206 | The authors make \fBno warranty\fR, implied or otherwise, about the | |
207 | suitability of this software for safety or security purposes. | |
208 | .PP | |
209 | The authors shall not in any case be liable for special, incidental, | |
210 | consequential, indirect or other similar damages arising from the use | |
211 | of this software. | |
212 | .PP | |
213 | Your mileage will vary. If in any doubt \fBdo not use it\fR. | |
214 | .Sh "\s-1RECENT\s0 \s-1CHANGES\s0" | |
215 | .IX Subsection "RECENT CHANGES" | |
216 | The interface to the Safe module has changed quite dramatically since | |
217 | version 1 (as supplied with Perl5.002). Study these pages carefully if | |
218 | you have code written to use Safe version 1 because you will need to | |
219 | makes changes. | |
220 | .Sh "Methods in class Safe" | |
221 | .IX Subsection "Methods in class Safe" | |
222 | To create a new compartment, use | |
223 | .PP | |
224 | .Vb 1 | |
225 | \& $cpt = new Safe; | |
226 | .Ve | |
227 | .PP | |
228 | Optional argument is (\s-1NAMESPACE\s0), where \s-1NAMESPACE\s0 is the root namespace | |
229 | to use for the compartment (defaults to \*(L"Safe::Root0\*(R", incremented for | |
230 | each new compartment). | |
231 | .PP | |
232 | Note that version 1.00 of the Safe module supported a second optional | |
233 | parameter, \s-1MASK\s0. That functionality has been withdrawn pending deeper | |
234 | consideration. Use the permit and deny methods described below. | |
235 | .PP | |
236 | The following methods can then be used on the compartment | |
237 | object returned by the above constructor. The object argument | |
238 | is implicit in each case. | |
239 | .IP "permit (\s-1OP\s0, ...)" 8 | |
240 | .IX Item "permit (OP, ...)" | |
241 | Permit the listed operators to be used when compiling code in the | |
242 | compartment (in \fIaddition\fR to any operators already permitted). | |
243 | .Sp | |
244 | You can list opcodes by names, or use a tag name; see | |
245 | \&\*(L"Predefined Opcode Tags\*(R" in Opcode. | |
246 | .IP "permit_only (\s-1OP\s0, ...)" 8 | |
247 | .IX Item "permit_only (OP, ...)" | |
248 | Permit \fIonly\fR the listed operators to be used when compiling code in | |
249 | the compartment (\fIno\fR other operators are permitted). | |
250 | .IP "deny (\s-1OP\s0, ...)" 8 | |
251 | .IX Item "deny (OP, ...)" | |
252 | Deny the listed operators from being used when compiling code in the | |
253 | compartment (other operators may still be permitted). | |
254 | .IP "deny_only (\s-1OP\s0, ...)" 8 | |
255 | .IX Item "deny_only (OP, ...)" | |
256 | Deny \fIonly\fR the listed operators from being used when compiling code | |
257 | in the compartment (\fIall\fR other operators will be permitted). | |
258 | .IP "trap (\s-1OP\s0, ...)" 8 | |
259 | .IX Item "trap (OP, ...)" | |
260 | .PD 0 | |
261 | .IP "untrap (\s-1OP\s0, ...)" 8 | |
262 | .IX Item "untrap (OP, ...)" | |
263 | .PD | |
264 | The trap and untrap methods are synonyms for deny and permit | |
265 | respectfully. | |
266 | .IP "share (\s-1NAME\s0, ...)" 8 | |
267 | .IX Item "share (NAME, ...)" | |
268 | This shares the variable(s) in the argument list with the compartment. | |
269 | This is almost identical to exporting variables using the Exporter | |
270 | module. | |
271 | .Sp | |
272 | Each \s-1NAME\s0 must be the \fBname\fR of a non-lexical variable, typically | |
273 | with the leading type identifier included. A bareword is treated as a | |
274 | function name. | |
275 | .Sp | |
276 | Examples of legal names are '$foo' for a scalar, '@foo' for an | |
277 | array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo' | |
278 | for a glob (i.e. all symbol table entries associated with \*(L"foo\*(R", | |
279 | including scalar, array, hash, sub and filehandle). | |
280 | .Sp | |
281 | Each \s-1NAME\s0 is assumed to be in the calling package. See share_from | |
282 | for an alternative method (which share uses). | |
283 | .IP "share_from (\s-1PACKAGE\s0, \s-1ARRAYREF\s0)" 8 | |
284 | .IX Item "share_from (PACKAGE, ARRAYREF)" | |
285 | This method is similar to \fIshare()\fR but allows you to explicitly name the | |
286 | package that symbols should be shared from. The symbol names (including | |
287 | type characters) are supplied as an array reference. | |
288 | .Sp | |
289 | .Vb 1 | |
290 | \& $safe->share_from('main', [ '$foo', '%bar', 'func' ]); | |
291 | .Ve | |
292 | .IP "varglob (\s-1VARNAME\s0)" 8 | |
293 | .IX Item "varglob (VARNAME)" | |
294 | This returns a glob reference for the symbol table entry of \s-1VARNAME\s0 in | |
295 | the package of the compartment. \s-1VARNAME\s0 must be the \fBname\fR of a | |
296 | variable without any leading type marker. For example, | |
297 | .Sp | |
298 | .Vb 4 | |
299 | \& $cpt = new Safe 'Root'; | |
300 | \& $Root::foo = "Hello world"; | |
301 | \& # Equivalent version which doesn't need to know $cpt's package name: | |
302 | \& ${$cpt->varglob('foo')} = "Hello world"; | |
303 | .Ve | |
304 | .IP "reval (\s-1STRING\s0)" 8 | |
305 | .IX Item "reval (STRING)" | |
306 | This evaluates \s-1STRING\s0 as perl code inside the compartment. | |
307 | .Sp | |
308 | The code can only see the compartment's namespace (as returned by the | |
309 | \&\fBroot\fR method). The compartment's root package appears to be the | |
310 | \&\f(CW\*(C`main::\*(C'\fR package to the code inside the compartment. | |
311 | .Sp | |
312 | Any attempt by the code in \s-1STRING\s0 to use an operator which is not permitted | |
313 | by the compartment will cause an error (at run-time of the main program | |
314 | but at compile-time for the code in \s-1STRING\s0). The error is of the form | |
315 | \&\*(L"'%s' trapped by operation mask...\*(R". | |
316 | .Sp | |
317 | If an operation is trapped in this way, then the code in \s-1STRING\s0 will | |
318 | not be executed. If such a trapped operation occurs or any other | |
319 | compile-time or return error, then $@ is set to the error message, just | |
320 | as with an \fIeval()\fR. | |
321 | .Sp | |
322 | If there is no error, then the method returns the value of the last | |
323 | expression evaluated, or a return statement may be used, just as with | |
324 | subroutines and \fB\f(BIeval()\fB\fR. The context (list or scalar) is determined | |
325 | by the caller as usual. | |
326 | .Sp | |
327 | This behaviour differs from the beta distribution of the Safe extension | |
328 | where earlier versions of perl made it hard to mimic the return | |
329 | behaviour of the \fIeval()\fR command and the context was always scalar. | |
330 | .Sp | |
331 | Some points to note: | |
332 | .Sp | |
333 | If the entereval op is permitted then the code can use eval \*(L"...\*(R" to | |
334 | \&'hide' code which might use denied ops. This is not a major problem | |
335 | since when the code tries to execute the eval it will fail because the | |
336 | opmask is still in effect. However this technique would allow clever, | |
337 | and possibly harmful, code to 'probe' the boundaries of what is | |
338 | possible. | |
339 | .Sp | |
340 | Any string eval which is executed by code executing in a compartment, | |
341 | or by code called from code executing in a compartment, will be eval'd | |
342 | in the namespace of the compartment. This is potentially a serious | |
343 | problem. | |
344 | .Sp | |
345 | Consider a function \fIfoo()\fR in package pkg compiled outside a compartment | |
346 | but shared with it. Assume the compartment has a root package called | |
347 | \&'Root'. If \fIfoo()\fR contains an eval statement like eval '$foo = 1' then, | |
348 | normally, \f(CW$pkg::foo\fR will be set to 1. If \fIfoo()\fR is called from the | |
349 | compartment (by whatever means) then instead of setting \f(CW$pkg::foo\fR, the | |
350 | eval will actually set \f(CW$Root::pkg::foo\fR. | |
351 | .Sp | |
352 | This can easily be demonstrated by using a module, such as the Socket | |
353 | module, which uses eval \*(L"...\*(R" as part of an \s-1AUTOLOAD\s0 function. You can | |
354 | \&'use' the module outside the compartment and share an (autoloaded) | |
355 | function with the compartment. If an autoload is triggered by code in | |
356 | the compartment, or by any code anywhere that is called by any means | |
357 | from the compartment, then the eval in the Socket module's \s-1AUTOLOAD\s0 | |
358 | function happens in the namespace of the compartment. Any variables | |
359 | created or used by the eval'd code are now under the control of | |
360 | the code in the compartment. | |
361 | .Sp | |
362 | A similar effect applies to \fIall\fR runtime symbol lookups in code | |
363 | called from a compartment but not compiled within it. | |
364 | .IP "rdo (\s-1FILENAME\s0)" 8 | |
365 | .IX Item "rdo (FILENAME)" | |
366 | This evaluates the contents of file \s-1FILENAME\s0 inside the compartment. | |
367 | See above documentation on the \fBreval\fR method for further details. | |
368 | .IP "root (\s-1NAMESPACE\s0)" 8 | |
369 | .IX Item "root (NAMESPACE)" | |
370 | This method returns the name of the package that is the root of the | |
371 | compartment's namespace. | |
372 | .Sp | |
373 | Note that this behaviour differs from version 1.00 of the Safe module | |
374 | where the root module could be used to change the namespace. That | |
375 | functionality has been withdrawn pending deeper consideration. | |
376 | .IP "mask (\s-1MASK\s0)" 8 | |
377 | .IX Item "mask (MASK)" | |
378 | This is a get-or-set method for the compartment's operator mask. | |
379 | .Sp | |
380 | With no \s-1MASK\s0 argument present, it returns the current operator mask of | |
381 | the compartment. | |
382 | .Sp | |
383 | With the \s-1MASK\s0 argument present, it sets the operator mask for the | |
384 | compartment (equivalent to calling the deny_only method). | |
385 | .Sh "Some Safety Issues" | |
386 | .IX Subsection "Some Safety Issues" | |
387 | This section is currently just an outline of some of the things code in | |
388 | a compartment might do (intentionally or unintentionally) which can | |
389 | have an effect outside the compartment. | |
390 | .IP "Memory" 8 | |
391 | .IX Item "Memory" | |
392 | Consuming all (or nearly all) available memory. | |
393 | .IP "\s-1CPU\s0" 8 | |
394 | .IX Item "CPU" | |
395 | Causing infinite loops etc. | |
396 | .IP "Snooping" 8 | |
397 | .IX Item "Snooping" | |
398 | Copying private information out of your system. Even something as | |
399 | simple as your user name is of value to others. Much useful information | |
400 | could be gleaned from your environment variables for example. | |
401 | .IP "Signals" 8 | |
402 | .IX Item "Signals" | |
403 | Causing signals (especially \s-1SIGFPE\s0 and \s-1SIGALARM\s0) to affect your process. | |
404 | .Sp | |
405 | Setting up a signal handler will need to be carefully considered | |
406 | and controlled. What mask is in effect when a signal handler | |
407 | gets called? If a user can get an imported function to get an | |
408 | exception and call the user's signal handler, does that user's | |
409 | restricted mask get re-instated before the handler is called? | |
410 | Does an imported handler get called with its original mask or | |
411 | the user's one? | |
412 | .IP "State Changes" 8 | |
413 | .IX Item "State Changes" | |
414 | Ops such as chdir obviously effect the process as a whole and not just | |
415 | the code in the compartment. Ops such as rand and srand have a similar | |
416 | but more subtle effect. | |
417 | .Sh "\s-1AUTHOR\s0" | |
418 | .IX Subsection "AUTHOR" | |
419 | Originally designed and implemented by Malcolm Beattie, | |
420 | mbeattie@sable.ox.ac.uk. | |
421 | .PP | |
422 | Reworked to use the Opcode module and other changes added by Tim Bunce | |
423 | <\fITim.Bunce@ig.co.uk\fR>. |