1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
|
/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@cs.vu.nl
WWW: http://www.swi-prolog.org
Copyright (C): 2009-2013, VU University Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(sandbox,
[ safe_goal/1 % :Goal
]).
:- use_module(library(assoc)).
:- use_module(library(lists)).
:- use_module(library(debug)).
:- use_module(library(apply_macros), [expand_phrase/2]).
:- multifile
safe_primitive/1, % Goal
safe_meta/2. % Goal, Calls
% :- debug(sandbox).
/** <module> Sandboxed Prolog code
Prolog is a full-featured Turing complete programming language in which
it is easy to write programs that can harm your computer. On the other
hand, Prolog is a logic based _query language_ which can be exploited to
query data interactively from, e.g., the web. This library provides
safe_goal/1, which determines whether it is safe to call its argument.
@tbd Handling of ^ and // meta predicates
*/
:- meta_predicate
safe_goal(0).
%% safe_goal(:Goal) is det.
%
% True if calling Goal provides no security risc. This implies
% that:
%
% - The call-graph can be fully expanded. Full expansion *stops*
% if a meta-goal is found for which we cannot determine enough
% details to know which predicate will be called.
%
% - All predicates referenced from the fully expanded are
% whitelisted by the predicate safe_primitive/1 and safe_meta/2.
%
% @error instantiation_error if the analysis encounters a term in
% a callable position that is insufficiently instantiated
% to determine the predicate called.
% @error permission_error(call, sandboxed, Goal) if Goal is in
% the call-tree and not white-listed.
safe_goal(M:Goal) :-
empty_assoc(Safe0),
safe(Goal, M, [], Safe0, _).
%% safe(+Goal, +Module, +Parents, +Safe0, -Safe) is semidet.
%
% Is true if Goal can only call safe code.
safe(V, _, Parents, _, _) :-
var(V), !,
throw(error(instantiation_error, sandbox(V, Parents))).
safe(M:G, _, Parent, Safe0, Safe) :- !,
safe(G, M, Parent, Safe0, Safe).
safe(G, _, Parents, _, _) :-
debugging(sandbox(show)),
length(Parents, Level),
debug(sandbox(show), '[~D] SAFE ~q?', [Level, G]),
fail.
safe(G, _, _, Safe, Safe) :-
safe_primitive(G),
predicate_property(G, iso), !.
safe(G, M, _, Safe, Safe) :-
( predicate_property(M:G, imported_from(M2))
-> true
; M2 = M
),
safe_primitive(M2:G), !.
safe(G, M, Parents, Safe0, Safe) :-
safe_meta(G, Called), !,
safe_list(Called, M, Parents, Safe0, Safe).
safe(G, M, Parents, Safe0, Safe) :-
goal_id(M:G, Id, Gen),
( get_assoc(Id, Safe0, _)
-> Safe = Safe0
; put_assoc(Id, Safe0, true, Safe1),
safe_clauses(Gen, M, [Id|Parents], Safe1, Safe)
).
safe_clauses(G, M, Parents, Safe0, Safe) :-
predicate_property(M:G, interpreted), !,
% \+ predicate_property(M:G, meta_predicate(_)), !,
def_module(M:G, MD:QG),
findall(Body, clause(MD:QG, Body), Bodies),
safe_list(Bodies, MD, Parents, Safe0, Safe).
safe_clauses(_, _M, [G|Parents], _, _) :-
throw(error(permission_error(call, sandboxed, G),
sandbox(G, Parents))).
safe_list([], _, _, Safe, Safe).
safe_list([H|T], M, Parents, Safe0, Safe) :-
copy_term(H, H1),
safe(H1, M, Parents, Safe0, Safe1),
safe_list(T, M, Parents, Safe1, Safe).
def_module(M:G, MD:QG) :-
predicate_property(M:G, imported_from(MD)), !,
meta_qualify(MD:G, M, QG).
def_module(M:G, M:QG) :-
meta_qualify(M:G, M, QG).
%% meta_qualify(:G, +M, -QG) is det.
%
% Perform meta-qualification of the goal-argument
meta_qualify(MD:G, M, QG) :-
predicate_property(MD:G, meta_predicate(Head)), !,
G =.. [Name|Args],
Head =.. [_|Q],
qualify_args(Q, M, Args, QArgs),
QG =.. [Name|QArgs].
meta_qualify(_:G, _, G).
qualify_args([], _, [], []).
qualify_args([H|T], M, [A|AT], [Q|QT]) :-
qualify_arg(H, M, A, Q),
qualify_args(T, M, AT, QT).
qualify_arg(S, M, A, Q) :-
q_arg(S), !,
qualify(A, M, Q).
qualify_arg(_, _, A, A).
q_arg(I) :- integer(I), !.
q_arg(:).
qualify(A, M, MZ:Q) :-
strip_module(M:A, MZ, Q).
%% goal_id(:Goal, -Id, -Gen) is nondet.
%
% Generate an identifier for the goal proven to be safe. We
% first try to prove the most general form of the goal. If
% this fails, we try to prove more specific versions.
%
% @tbd Do step-by-step generalisation instead of the current
% two levels (most general and most specific).
%
goal_id(M:Goal, M:Id, Gen) :- !,
goal_id(Goal, Id, Gen).
goal_id(Term, _, _) :-
\+ callable(Term), !, fail.
goal_id(Term, Name/Arity, Gen) :- % most general form
functor(Term, Name, Arity),
functor(Gen, Name, Arity).
goal_id(Term, Skolem, Term) :- % most specific form
copy_term(Term, Skolem),
numbervars(Skolem, 0, _).
%% safe_primitive(?Goal) is nondet.
%
% True if Goal is safe to call (i.e., cannot access dangerous
% system-resources and cannot upset other parts of the Prolog
% process). There are two types of facts. ISO built-ins are
% declared without a module prefix. This is safe because it is not
% allowed to (re-)define these primitives (i.e., give them an
% unsafe implementation) and the way around
% (redefine_system_predicate/1) is unsafe. The other group are
% module-qualified and only match if the system infers that the
% predicate is (or will be) imported from the given module.
% First, all ISO system predicates that are considered safe
safe_primitive(true).
safe_primitive(fail).
safe_primitive(repeat).
safe_primitive(!).
% types
safe_primitive(var(_)).
safe_primitive(nonvar(_)).
safe_primitive(integer(_)).
safe_primitive(float(_)).
safe_primitive(number(_)).
safe_primitive(atom(_)).
safe_primitive(compound(_)).
safe_primitive(ground(_)).
% ordering
safe_primitive(@>(_,_)).
safe_primitive(@>=(_,_)).
safe_primitive(==(_,_)).
safe_primitive(@<(_,_)).
safe_primitive(@=<(_,_)).
safe_primitive(compare(_,_,_)).
safe_primitive(sort(_,_)).
safe_primitive(keysort(_,_)).
% unification and equivalence
safe_primitive(=(_,_)).
safe_primitive(\=(_,_)).
safe_primitive(\==(_,_)).
% arithmetic
safe_primitive(is(_,_)).
safe_primitive(>(_,_)).
safe_primitive(>=(_,_)).
safe_primitive(=:=(_,_)).
safe_primitive(=\=(_,_)).
safe_primitive(=<(_,_)).
safe_primitive(<(_,_)).
% term-handling
safe_primitive(arg(_,_,_)).
safe_primitive(system:setarg(_,_,_)).
safe_primitive(functor(_,_,_)).
safe_primitive(_ =.. _).
safe_primitive(copy_term(_,_)).
safe_primitive(numbervars(_,_,_)).
% atoms
safe_primitive(atom_concat(_,_,_)).
safe_primitive(atom_chars(_, _)).
% Lists
safe_primitive(length(_,_)).
% exceptions
safe_primitive(throw(_)).
% misc
safe_primitive(current_prolog_flag(_,_)).
safe_primitive(clause(_,_)).
safe_primitive(asserta(X)) :- safe_assert(X).
safe_primitive(assertz(X)) :- safe_assert(X).
safe_primitive(retract(X)) :- safe_assert(X).
safe_primitive(retractall(X)) :- safe_assert(X).
% The non-ISO system predicates. These can be redefined, so we must
% be careful to ensure the system ones are used.
safe_primitive(system:false).
safe_primitive(system:cyclic_term(_)).
safe_primitive(system:msort(_,_)).
safe_primitive(system:between(_,_,_)).
safe_primitive(system:succ(_,_)).
safe_primitive(system:plus(_,_,_)).
safe_primitive(system:term_variables(_,_)).
safe_primitive(system:atom_to_term(_,_,_)).
safe_primitive(system:term_to_atom(_,_)).
safe_primitive(system:atomic_list_concat(_,_,_)).
safe_primitive(system:atomic_list_concat(_,_)).
safe_primitive(system:downcase_atom(_,_)).
safe_primitive(system:upcase_atom(_,_)).
safe_primitive(system:is_list(_)).
safe_primitive(system:memberchk(_,_)).
safe_primitive(system:'$skip_list'(_,_,_)).
% attributes
safe_primitive(system:get_attr(_,_,_)).
safe_primitive(system:del_attr(_,_)).
% globals
safe_primitive(system:b_getval(_,_)).
safe_primitive(system:b_setval(_,_)).
safe_primitive(system:nb_current(_,_)).
safe_primitive(system:assert(X)) :-
safe_assert(X).
% use_module/1. We only allow for .pl files that are loaded from
% relative paths that do not contain /../
safe_primitive(system:use_module(Spec)) :-
ground(Spec),
( atom(Spec)
-> Path = Spec
; Spec =.. [_Alias, Segments],
phrase(segments_to_path(Segments), List),
atomic_list_concat(List, Path)
),
\+ is_absolute_file_name(Path),
\+ sub_atom(Path, _, _, _, '/../'),
absolute_file_name(Spec, AbsFile,
[ access(read),
file_type(prolog),
file_errors(fail)
]),
file_name_extension(_, Ext, AbsFile),
save_extension(Ext).
% Other library predicates.
% rdf
safe_primitive(rdf_db:rdf(_,_,_)).
safe_primitive(rdf_db:rdf(_,_,_,_)).
% http
safe_primitive(http_session:http_session_data(_)).
safe_primitive(http_session:http_session_id(_)).
% random
safe_primitive(random:random(_)).
% porter
safe_primitive(porter_stem:porter_stem(_,_)).
safe_primitive(porter_stem:unaccent_atom(_,_)).
safe_primitive(porter_stem:tokenize_atom(_,_)).
safe_primitive(porter_stem:atom_to_stem_list(_,_)).
% support predicates for safe_primitive, validating the safety of
% arguments to certain goals.
segments_to_path(A/B) --> !,
segments_to_path(A),
[/],
segments_to_path(B).
segments_to_path(X) -->
[X].
save_extension(pl).
%% safe_assert(+Term) is semidet.
%
% True if assert(Term) is safe, which means it asserts in the
% current module. Cross-module asserts are considered unsafe. We
% only allow for adding facts. In theory, we could also allow for
% rules if we prove the safety of the body.
safe_assert(C) :- cyclic_term(C), !, fail.
safe_assert(X) :- var(X), !, fail.
safe_assert(_Head:-_Body) :- !, fail.
safe_assert(_:_) :- !, fail.
safe_assert(_).
%% safe_meta(+Goal, -Called) is semidet.
%
% True if Goal is a meta-predicate that is considered safe iff all
% elements in Called are safe.
safe_meta(put_attr(_,M,A), [M:attr_unify_hook(A, _)]) :-
atom(M), !.
safe_meta(Phrase, [Goal]) :-
expand_phrase(Phrase, Goal), !.
safe_meta(Goal, Called) :-
generic_goal(Goal, Gen),
safe_meta(Gen),
findall(C, called(Gen, Goal, C), Called).
called(Gen, Goal, Called) :-
arg(I, Gen, Spec),
integer(Spec),
arg(I, Goal, Called0),
extend(Spec, Called0, Called).
generic_goal(G, Gen) :-
functor(G, Name, Arity),
functor(Gen, Name, Arity).
extend(0, G, G) :- !.
extend(I, G0, G) :-
G0 =.. List,
length(Extra, I),
append(List, Extra, All),
G =.. All.
safe_meta((0,0)).
safe_meta((0;0)).
safe_meta((0->0)).
safe_meta(forall(0,0)).
safe_meta(catch(0,_,0)).
safe_meta(findall(_,0,_)).
safe_meta(findall(_,0,_,_)).
safe_meta(setof(_,0,_)). % TBD
safe_meta(bagof(_,0,_)).
safe_meta(^(_,0)).
safe_meta(\+(0)).
safe_meta(maplist(1, _)).
safe_meta(maplist(2, _, _)).
safe_meta(maplist(3, _, _, _)).
safe_meta(call(0)).
safe_meta(call(1, _)).
safe_meta(call(2, _, _)).
safe_meta(call(3, _, _, _)).
safe_meta(call(4, _, _, _, _)).
safe_meta(call(5, _, _, _, _, _)).
/*******************************
* SAFE COMPILATION HOOKS *
*******************************/
:- multifile
prolog:sandbox_allowed_directive/1,
prolog:sandbox_allowed_expansion/1.
%% prolog:sandbox_allowed_directive(:G) is det.
%
% Throws an exception if G is not considered a safe directive.
prolog:sandbox_allowed_directive(M:PredAttr) :-
safe_directive(PredAttr),
( prolog_load_context(module, M)
-> PredAttr =.. [Attr, Preds],
safe_pattr(Preds, Attr)
; permission_error(directive, sandboxed, (:- M:PredAttr))
).
prolog:sandbox_allowed_directive(G) :-
safe_goal(G).
safe_directive(dynamic(_)).
safe_directive(thread_local(_)).
safe_directive(discontiguous(_)).
safe_directive(public(_)).
safe_pattr(Var, _) :-
var(Var), !,
instantiation_error(Var).
safe_pattr((A,B), Attr) :- !,
safe_pattr(A, Attr),
safe_pattr(B, Attr).
safe_pattr(M:G, Attr) :- !,
( atom(M),
prolog_load_context(module, M)
-> true
; Goal =.. [Attr,M:G],
permission_error(directive, sandboxed, (:- Goal))
).
safe_pattr(_, _).
%% prolog:sandbox_allowed_expansion(:G) is det.
%
% Throws an exception if G is not considered a safe expansion
% goal. This deals with call-backs from the compiler for
%
% - goal_expansion/2
% - term_expansion/2
% - Quasi quotations.
prolog:sandbox_allowed_expansion(G) :-
safe_goal(G).
% tuProlog compatibility
system:quicksort(L, <, S) :- msort(L, S).
system:quicksort(L, @<, S) :- msort(L, S).
|