1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2013-2023, VU University Amsterdam
    7                              CWI, Amsterdam
    8                              SWI-Prolog Solutions b.v
    9    All rights reserved.
   10
   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
   14
   15    1. Redistributions of source code must retain the above copyright
   16       notice, this list of conditions and the following disclaimer.
   17
   18    2. Redistributions in binary form must reproduce the above copyright
   19       notice, this list of conditions and the following disclaimer in
   20       the documentation and/or other materials provided with the
   21       distribution.
   22
   23    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   25    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   26    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   27    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   28    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   29    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   30    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   31    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   33    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   34    POSSIBILITY OF SUCH DAMAGE.
   35*/
   36
   37:- module(sandbox,
   38          [ safe_goal/1,                % :Goal
   39            safe_call/1                 % :Goal
   40          ]).   41:- use_module(library(apply_macros),[expand_phrase/2]).   42:- use_module(library(apply),[maplist/2]).   43:- use_module(library(assoc),[empty_assoc/1,get_assoc/3,put_assoc/4]).   44:- use_module(library(debug),[debug/3,debugging/1]).   45:- use_module(library(error),
   46              [ must_be/2,
   47                instantiation_error/1,
   48                type_error/2,
   49                permission_error/3
   50              ]).   51:- use_module(library(lists),[append/3]).   52:- use_module(library(prolog_format),[format_types/2]).   53
   54:- multifile
   55    safe_primitive/1,               % Goal
   56    safe_meta_predicate/1,          % Name/Arity
   57    safe_meta/2,                    % Goal, Calls
   58    safe_meta/3,                    % Goal, Context, Calls
   59    safe_global_variable/1,         % Name
   60    safe_directive/1,               % Module:Goal
   61    safe_prolog_flag/2.             % +Name, +Value
   62
   63% :- debug(sandbox).
   64
   65/** <module> Sandboxed Prolog code
   66
   67Prolog is a full-featured Turing complete  programming language in which
   68it is easy to write programs that can   harm your computer. On the other
   69hand, Prolog is a logic based _query language_ which can be exploited to
   70query data interactively from, e.g.,  the   web.  This  library provides
   71safe_goal/1, which determines whether it is safe to call its argument.
   72
   73@tbd    Handling of ^ and // meta predicates
   74@tbd    Complete set of whitelisted predicates
   75@see    http://www.swi-prolog.org/pldoc/package/pengines.html
   76*/
   77
   78
   79:- meta_predicate
   80    safe_goal(:),
   81    safe_call(0).   82
   83%!  safe_call(:Goal)
   84%
   85%   Call Goal if it  complies  with   the  sandboxing  rules. Before
   86%   calling   Goal,   it   performs   expand_goal/2,   followed   by
   87%   safe_goal/1. Expanding is done explicitly  because situations in
   88%   which safe_call/1 typically concern goals that  are not known at
   89%   compile time.
   90%
   91%   @see safe_goal/1.
   92
   93safe_call(Goal0) :-
   94    expand_goal(Goal0, Goal),
   95    safe_goal(Goal),
   96    call(Goal).
   97
   98%!  safe_goal(:Goal) is det.
   99%
  100%   True if calling Goal provides  no   security  risc. This implies
  101%   that:
  102%
  103%     - The call-graph can be fully expanded. Full expansion *stops*
  104%     if a meta-goal is found for   which we cannot determine enough
  105%     details to know which predicate will be called.
  106%
  107%     - All predicates  referenced  from   the  fully  expanded  are
  108%     whitelisted by the predicate safe_primitive/1 and safe_meta/2.
  109%
  110%     - It is not allowed to make explicitly qualified calls into
  111%     modules to predicates that are not exported or declared
  112%     public.
  113%
  114%   @error  instantiation_error if the analysis encounters a term in
  115%           a callable position that is insufficiently instantiated
  116%           to determine the predicate called.
  117%   @error  permission_error(call, sandboxed, Goal) if Goal is in
  118%           the call-tree and not white-listed.
  119
  120safe_goal(M:Goal) :-
  121    empty_assoc(Safe0),
  122    catch(safe(Goal, M, [], Safe0, _), E, true),
  123    !,
  124    nb_delete(sandbox_last_error),
  125    (   var(E)
  126    ->  true
  127    ;   throw(E)
  128    ).
  129safe_goal(_) :-
  130    nb_current(sandbox_last_error, E),
  131    !,
  132    nb_delete(sandbox_last_error),
  133    throw(E).
  134safe_goal(G) :-
  135    debug(sandbox(fail), 'safe_goal/1 failed for ~p', [G]),
  136    throw(error(instantiation_error, sandbox(G, []))).
  137
  138
  139%!  safe(+Goal, +Module, +Parents, +Safe0, -Safe) is semidet.
  140%
  141%   Is true if Goal can only call safe code.
  142
  143safe(V, _, Parents, _, _) :-
  144    var(V),
  145    !,
  146    Error = error(instantiation_error, sandbox(V, Parents)),
  147    nb_setval(sandbox_last_error, Error),
  148    throw(Error).
  149safe(M:G, _, Parents, Safe0, Safe) :-
  150    !,
  151    must_be(atom, M),
  152    must_be(callable, G),
  153    known_module(M:G, Parents),
  154    (   predicate_property(M:G, imported_from(M2))
  155    ->  true
  156    ;   M2 = M
  157    ),
  158    (   (   safe_primitive(M2:G)
  159        ;   safe_primitive(G),
  160            predicate_property(G, iso)
  161        )
  162    ->  Safe = Safe0
  163    ;   (   predicate_property(M:G, exported)
  164        ;   predicate_property(M:G, public)
  165        ;   predicate_property(M:G, multifile)
  166        ;   predicate_property(M:G, iso)
  167        ;   memberchk(M:_, Parents)
  168        )
  169    ->  safe(G, M, Parents, Safe0, Safe)
  170    ;   throw(error(permission_error(call, sandboxed, M:G),
  171                    sandbox(M:G, Parents)))
  172    ).
  173safe(G, _, Parents, _, _) :-
  174    debugging(sandbox(show)),
  175    length(Parents, Level),
  176    debug(sandbox(show), '[~D] SAFE ~q?', [Level, G]),
  177    fail.
  178safe(G, _, Parents, Safe, Safe) :-
  179    catch(safe_primitive(G),
  180          error(instantiation_error, _),
  181          rethrow_instantition_error([G|Parents])),
  182    predicate_property(G, iso),
  183    !.
  184safe(G, M, Parents, Safe, Safe) :-
  185    known_module(M:G, Parents),
  186    (   predicate_property(M:G, imported_from(M2))
  187    ->  true
  188    ;   M2 = M
  189    ),
  190    (   catch(safe_primitive(M2:G),
  191              error(instantiation_error, _),
  192              rethrow_instantition_error([M2:G|Parents]))
  193    ;   predicate_property(M2:G, number_of_rules(0))
  194    ),
  195    !.
  196safe(G, M, Parents, Safe0, Safe) :-
  197    predicate_property(G, iso),
  198    safe_meta_call(G, M, Called),
  199    !,
  200    add_iso_parent(G, Parents, Parents1),
  201    safe_list(Called, M, Parents1, Safe0, Safe).
  202safe(G, M, Parents, Safe0, Safe) :-
  203    (   predicate_property(M:G, imported_from(M2))
  204    ->  true
  205    ;   M2 = M
  206    ),
  207    safe_meta_call(M2:G, M, Called),
  208    !,
  209    safe_list(Called, M, Parents, Safe0, Safe).
  210safe(G, M, Parents, Safe0, Safe) :-
  211    goal_id(M:G, Id, Gen),
  212    (   get_assoc(Id, Safe0, _)
  213    ->  Safe = Safe0
  214    ;   put_assoc(Id, Safe0, true, Safe1),
  215        (   Gen == M:G
  216        ->  safe_clauses(Gen, M, [Id|Parents], Safe1, Safe)
  217        ;   catch(safe_clauses(Gen, M, [Id|Parents], Safe1, Safe),
  218                  error(instantiation_error, Ctx),
  219                  unsafe(Parents, Ctx))
  220        )
  221    ),
  222    !.
  223safe(G, M, Parents, _, _) :-
  224    debug(sandbox(fail),
  225          'safe/1 failed for ~p (parents:~p)', [M:G, Parents]),
  226    fail.
  227
  228unsafe(Parents, Var) :-
  229    var(Var),
  230    !,
  231    nb_setval(sandbox_last_error,
  232              error(instantiation_error, sandbox(_, Parents))),
  233    fail.
  234unsafe(_Parents, Ctx) :-
  235    Ctx = sandbox(_,_),
  236    nb_setval(sandbox_last_error,
  237              error(instantiation_error, Ctx)),
  238    fail.
  239
  240rethrow_instantition_error(Parents) :-
  241    throw(error(instantiation_error, sandbox(_, Parents))).
  242
  243safe_clauses(G, M, Parents, Safe0, Safe) :-
  244    predicate_property(M:G, interpreted),
  245    def_module(M:G, MD:QG),
  246    \+ compiled(MD:QG),
  247    !,
  248    findall(Ref-Body, clause(MD:QG, Body, Ref), Bodies),
  249    safe_bodies(Bodies, MD, Parents, Safe0, Safe).
  250safe_clauses(G, M, [_|Parents], _, _) :-
  251    predicate_property(M:G, visible),
  252    !,
  253    throw(error(permission_error(call, sandboxed, G),
  254                sandbox(M:G, Parents))).
  255safe_clauses(_, _, [G|Parents], _, _) :-
  256    throw(error(existence_error(procedure, G),
  257                sandbox(G, Parents))).
  258
  259compiled(system:(@(_,_))).
  260
  261known_module(M:_, _) :-
  262    current_module(M),
  263    !.
  264known_module(M:G, Parents) :-
  265    throw(error(permission_error(call, sandboxed, M:G),
  266                sandbox(M:G, Parents))).
  267
  268add_iso_parent(G, Parents, Parents) :-
  269    is_control(G),
  270    !.
  271add_iso_parent(G, Parents, [G|Parents]).
  272
  273is_control((_,_)).
  274is_control((_;_)).
  275is_control((_->_)).
  276is_control((_*->_)).
  277is_control(\+(_)).
  278
  279
  280%!  safe_bodies(+Bodies, +Module, +Parents, +Safe0, -Safe)
  281%
  282%   Verify the safety of bodies. If  a   clause  was compiled with a
  283%   qualified module, we  consider  execution  of   the  body  in  a
  284%   different module _not_ a cross-module call.
  285
  286safe_bodies([], _, _, Safe, Safe).
  287safe_bodies([Ref-H|T], M, Parents, Safe0, Safe) :-
  288    (   H = M2:H2, nonvar(M2),
  289        clause_property(Ref, module(M2))
  290    ->  copy_term(H2, H3),
  291        CM = M2
  292    ;   copy_term(H, H3),
  293        CM = M
  294    ),
  295    safe(H3, CM, Parents, Safe0, Safe1),
  296    safe_bodies(T, M, Parents, Safe1, Safe).
  297
  298def_module(M:G, MD:QG) :-
  299    predicate_property(M:G, imported_from(MD)),
  300    !,
  301    meta_qualify(MD:G, M, QG).
  302def_module(M:G, M:QG) :-
  303    meta_qualify(M:G, M, QG).
  304
  305%!  safe_list(+Called, +Module, +Parents, +Safe0, -Safe)
  306%
  307%   Processed objects called through meta  predicates. If the called
  308%   object  is  in  our  current  context    we  remove  the  module
  309%   qualification to avoid the cross-module check.
  310
  311safe_list([], _, _, Safe, Safe).
  312safe_list([H|T], M, Parents, Safe0, Safe) :-
  313    (   H = M2:H2,
  314        M == M2                             % in our context
  315    ->  copy_term(H2, H3)
  316    ;   copy_term(H, H3)                    % cross-module call
  317    ),
  318    safe(H3, M, Parents, Safe0, Safe1),
  319    safe_list(T, M, Parents, Safe1, Safe).
  320
  321%!  meta_qualify(:G, +M, -QG) is det.
  322%
  323%   Perform meta-qualification of the goal-argument
  324
  325meta_qualify(MD:G, M, QG) :-
  326    predicate_property(MD:G, meta_predicate(Head)),
  327    !,
  328    G =.. [Name|Args],
  329    Head =.. [_|Q],
  330    qualify_args(Q, M, Args, QArgs),
  331    QG =.. [Name|QArgs].
  332meta_qualify(_:G, _, G).
  333
  334qualify_args([], _, [], []).
  335qualify_args([H|T], M, [A|AT], [Q|QT]) :-
  336    qualify_arg(H, M, A, Q),
  337    qualify_args(T, M, AT, QT).
  338
  339qualify_arg(S, M, A, Q) :-
  340    q_arg(S),
  341    !,
  342    qualify(A, M, Q).
  343qualify_arg(_, _, A, A).
  344
  345q_arg(I) :- integer(I), !.
  346q_arg(:).
  347q_arg(^).
  348q_arg(//).
  349
  350qualify(A, M, MZ:Q) :-
  351    strip_module(M:A, MZ, Q).
  352
  353%!  goal_id(:Goal, -Id, -Gen) is nondet.
  354%
  355%   Generate an identifier for the goal proven to be safe. We
  356%   first try to prove the most general form of the goal.  If
  357%   this fails, we try to prove more specific versions.
  358%
  359%   @tbd    Do step-by-step generalisation instead of the current
  360%           two levels (most general and most specific).
  361%   @tbd    We could also use variant_sha1 for the goal ids.
  362
  363goal_id(M:Goal, M:Id, Gen) :-
  364    !,
  365    goal_id(Goal, Id, Gen).
  366goal_id(Var, _, _) :-
  367    var(Var),
  368    !,
  369    instantiation_error(Var).
  370goal_id(Atom, Atom, Atom) :-
  371    atom(Atom),
  372    !.
  373goal_id(Term, _, _) :-
  374    \+ compound(Term),
  375    !,
  376    type_error(callable, Term).
  377goal_id(Term, Skolem, Gen) :-           % most general form
  378    compound_name_arity(Term, Name, Arity),
  379    compound_name_arity(Skolem, Name, Arity),
  380    compound_name_arity(Gen, Name, Arity),
  381    copy_goal_args(1, Term, Skolem, Gen),
  382    (   Gen =@= Term
  383    ->  !                           % No more specific one; we can commit
  384    ;   true
  385    ),
  386    numbervars(Skolem, 0, _).
  387goal_id(Term, Skolem, Term) :-          % most specific form
  388    debug(sandbox(specify), 'Retrying with ~p', [Term]),
  389    copy_term(Term, Skolem),
  390    numbervars(Skolem, 0, _).
  391
  392%!  copy_goal_args(+I, +Term, +Skolem, +Gen) is det.
  393%
  394%   Create  the  most  general  form,   but  keep  module  qualified
  395%   arguments because they will likely be called anyway.
  396
  397copy_goal_args(I, Term, Skolem, Gen) :-
  398    arg(I, Term, TA),
  399    !,
  400    arg(I, Skolem, SA),
  401    arg(I, Gen, GA),
  402    copy_goal_arg(TA, SA, GA),
  403    I2 is I + 1,
  404    copy_goal_args(I2, Term, Skolem, Gen).
  405copy_goal_args(_, _, _, _).
  406
  407copy_goal_arg(Arg, SArg, Arg) :-
  408    copy_goal_arg(Arg),
  409    !,
  410    copy_term(Arg, SArg).
  411copy_goal_arg(_, _, _).
  412
  413copy_goal_arg(Var) :- var(Var), !, fail.
  414copy_goal_arg(_:_).
  415
  416%!  verify_safe_declaration(+Decl)
  417%
  418%   See whether a  safe  declaration  makes   sense.  That  is,  the
  419%   predicate must be defined (such that  the attacker cannot define
  420%   the predicate), must be sufficiently   instantiated and only ISO
  421%   declared predicates may omit a module qualification.
  422%
  423%   @tbd    Verify safe_meta/2 declarations.  It is a bit less clear
  424%           what the rules are.
  425
  426term_expansion(safe_primitive(Goal), Term) :-
  427    (   verify_safe_declaration(Goal)
  428    ->  Term = safe_primitive(Goal)
  429    ;   Term = []
  430    ).
  431term_expansion((safe_primitive(Goal) :- Body), Term) :-
  432    (   verify_safe_declaration(Goal)
  433    ->  Term = (safe_primitive(Goal) :- Body)
  434    ;   Term = []
  435    ).
  436
  437system:term_expansion(sandbox:safe_primitive(Goal), Term) :-
  438    \+ current_prolog_flag(xref, true),
  439    (   verify_safe_declaration(Goal)
  440    ->  Term = sandbox:safe_primitive(Goal)
  441    ;   Term = []
  442    ).
  443system:term_expansion((sandbox:safe_primitive(Goal) :- Body), Term) :-
  444    \+ current_prolog_flag(xref, true),
  445    (   verify_safe_declaration(Goal)
  446    ->  Term = (sandbox:safe_primitive(Goal) :- Body)
  447    ;   Term = []
  448    ).
  449
  450verify_safe_declaration(Var) :-
  451    var(Var),
  452    !,
  453    instantiation_error(Var).
  454verify_safe_declaration(Module:Goal) :-
  455    !,
  456    must_be(atom, Module),
  457    must_be(callable, Goal),
  458    (   ok_meta(Module:Goal)
  459    ->  true
  460    ;   (   predicate_property(Module:Goal, visible)
  461        ->  true
  462        ;   predicate_property(Module:Goal, foreign)
  463        ),
  464        \+ predicate_property(Module:Goal, imported_from(_)),
  465        \+ predicate_property(Module:Goal, meta_predicate(_))
  466    ->  true
  467    ;   permission_error(declare, safe_goal, Module:Goal)
  468    ).
  469verify_safe_declaration(Goal) :-
  470    must_be(callable, Goal),
  471    (   predicate_property(system:Goal, iso),
  472        \+ predicate_property(system:Goal, meta_predicate())
  473    ->  true
  474    ;   permission_error(declare, safe_goal, Goal)
  475    ).
  476
  477ok_meta(system:assert(_)).
  478ok_meta(system:load_files(_,_)).
  479ok_meta(system:use_module(_,_)).
  480ok_meta(system:use_module(_)).
  481ok_meta('$syspreds':predicate_property(_,_)).
  482
  483verify_predefined_safe_declarations :-
  484    forall(clause(safe_primitive(Goal), _Body, Ref),
  485           ( E = error(F,_),
  486             catch(verify_safe_declaration(Goal), E, true),
  487             (   nonvar(F)
  488             ->  clause_property(Ref, file(File)),
  489                 clause_property(Ref, line_count(Line)),
  490                 print_message(error, bad_safe_declaration(Goal, File, Line))
  491             ;   true
  492             )
  493           )).
  494
  495:- initialization(verify_predefined_safe_declarations, now).  496
  497%!  safe_primitive(?Goal) is nondet.
  498%
  499%   True if Goal is safe  to   call  (i.e.,  cannot access dangerous
  500%   system-resources and cannot upset  other   parts  of  the Prolog
  501%   process). There are two  types  of   facts.  ISO  built-ins  are
  502%   declared without a module prefix. This is safe because it is not
  503%   allowed to (re-)define these  primitives   (i.e.,  give  them an
  504%   unsafe     implementation)     and     the       way      around
  505%   (redefine_system_predicate/1) is unsafe.  The   other  group are
  506%   module-qualified and only match if the   system  infers that the
  507%   predicate is imported from the given module.
  508
  509% First, all ISO system predicates that are considered safe
  510
  511safe_primitive(true).
  512safe_primitive(fail).
  513safe_primitive(system:false).
  514safe_primitive(repeat).
  515safe_primitive(!).
  516                                        % types
  517safe_primitive(var(_)).
  518safe_primitive(nonvar(_)).
  519safe_primitive(system:attvar(_)).
  520safe_primitive(integer(_)).
  521safe_primitive(float(_)).
  522:- if(current_predicate(rational/1)).  523safe_primitive(system:rational(_)).
  524safe_primitive(system:rational(_,_,_)).
  525:- endif.  526safe_primitive(number(_)).
  527safe_primitive(atom(_)).
  528safe_primitive(system:blob(_,_)).
  529safe_primitive(system:string(_)).
  530safe_primitive(atomic(_)).
  531safe_primitive(compound(_)).
  532safe_primitive(callable(_)).
  533safe_primitive(ground(_)).
  534safe_primitive(system:nonground(_,_)).
  535safe_primitive(system:cyclic_term(_)).
  536safe_primitive(acyclic_term(_)).
  537safe_primitive(system:is_stream(_)).
  538safe_primitive(system:'$is_char'(_)).
  539safe_primitive(system:'$is_char_code'(_)).
  540safe_primitive(system:'$is_char_list'(_,_)).
  541safe_primitive(system:'$is_code_list'(_,_)).
  542                                        % ordering
  543safe_primitive(@>(_,_)).
  544safe_primitive(@>=(_,_)).
  545safe_primitive(==(_,_)).
  546safe_primitive(@<(_,_)).
  547safe_primitive(@=<(_,_)).
  548safe_primitive(compare(_,_,_)).
  549safe_primitive(sort(_,_)).
  550safe_primitive(keysort(_,_)).
  551safe_primitive(system: =@=(_,_)).
  552safe_primitive(system:'$btree_find_node'(_,_,_,_,_)).
  553
  554                                        % unification and equivalence
  555safe_primitive(=(_,_)).
  556safe_primitive(\=(_,_)).
  557safe_primitive(system:'?='(_,_)).
  558safe_primitive(system:unifiable(_,_,_)).
  559safe_primitive(unify_with_occurs_check(_,_)).
  560safe_primitive(\==(_,_)).
  561                                        % arithmetic
  562safe_primitive(is(_,_)).
  563safe_primitive(>(_,_)).
  564safe_primitive(>=(_,_)).
  565safe_primitive(=:=(_,_)).
  566safe_primitive(=\=(_,_)).
  567safe_primitive(=<(_,_)).
  568safe_primitive(<(_,_)).
  569:- if(current_prolog_flag(bounded, false)).  570safe_primitive(system:nth_integer_root_and_remainder(_,_,_,_)).
  571:- endif.  572safe_primitive(system:current_arithmetic_function(_)).
  573safe_primitive(system:bounded_number(_,_,_)).
  574safe_primitive(system:float_class(_,_)).
  575safe_primitive(system:float_parts(_,_,_,_)).
  576
  577                                        % term-handling
  578safe_primitive(arg(_,_,_)).
  579safe_primitive(system:setarg(_,_,_)).
  580safe_primitive(system:nb_setarg(_,_,_)).
  581safe_primitive(system:nb_linkarg(_,_,_)).
  582safe_primitive(functor(_,_,_)).
  583safe_primitive(system:functor(_,_,_,_)).
  584safe_primitive(_ =.. _).
  585safe_primitive(system:compound_name_arity(_,_,_)).
  586safe_primitive(system:compound_name_arguments(_,_,_)).
  587safe_primitive(system:'$filled_array'(_,_,_,_)).
  588safe_primitive(copy_term(_,_)).
  589safe_primitive(system:copy_term(_,_,_,_)).
  590safe_primitive(system:duplicate_term(_,_)).
  591safe_primitive(system:copy_term_nat(_,_)).
  592safe_primitive(system:size_abstract_term(_,_,_)).
  593safe_primitive(numbervars(_,_,_)).
  594safe_primitive(system:numbervars(_,_,_,_)).
  595safe_primitive(subsumes_term(_,_)).
  596safe_primitive(system:term_hash(_,_)).
  597safe_primitive(system:term_hash(_,_,_,_)).
  598safe_primitive(system:variant_sha1(_,_)).
  599safe_primitive(system:variant_hash(_,_)).
  600safe_primitive(system:'$term_size'(_,_,_)).
  601
  602                                        % dicts
  603safe_primitive(system:is_dict(_)).
  604safe_primitive(system:is_dict(_,_)).
  605safe_primitive(system:get_dict(_,_,_)).
  606safe_primitive(system:get_dict(_,_,_,_,_)).
  607safe_primitive(system:'$get_dict_ex'(_,_,_)).
  608safe_primitive(system:dict_create(_,_,_)).
  609safe_primitive(system:dict_pairs(_,_,_)).
  610safe_primitive(system:put_dict(_,_,_)).
  611safe_primitive(system:put_dict(_,_,_,_)).
  612safe_primitive(system:del_dict(_,_,_,_)).
  613safe_primitive(system:select_dict(_,_,_)).
  614safe_primitive(system:b_set_dict(_,_,_)).
  615safe_primitive(system:nb_set_dict(_,_,_)).
  616safe_primitive(system:nb_link_dict(_,_,_)).
  617safe_primitive(system:(:<(_,_))).
  618safe_primitive(system:(>:<(_,_))).
  619                                        % atoms
  620safe_primitive(atom_chars(_, _)).
  621safe_primitive(atom_codes(_, _)).
  622safe_primitive(sub_atom(_,_,_,_,_)).
  623safe_primitive(atom_concat(_,_,_)).
  624safe_primitive(atom_length(_,_)).
  625safe_primitive(char_code(_,_)).
  626safe_primitive(system:name(_,_)).
  627safe_primitive(system:atomic_concat(_,_,_)).
  628safe_primitive(system:atomic_list_concat(_,_)).
  629safe_primitive(system:atomic_list_concat(_,_,_)).
  630safe_primitive(system:downcase_atom(_,_)).
  631safe_primitive(system:upcase_atom(_,_)).
  632safe_primitive(system:char_type(_,_)).
  633safe_primitive(system:normalize_space(_,_)).
  634safe_primitive(system:sub_atom_icasechk(_,_,_)).
  635                                        % numbers
  636safe_primitive(number_codes(_,_)).
  637safe_primitive(number_chars(_,_)).
  638safe_primitive(system:atom_number(_,_)).
  639safe_primitive(system:code_type(_,_)).
  640                                        % strings
  641safe_primitive(system:atom_string(_,_)).
  642safe_primitive(system:number_string(_,_)).
  643safe_primitive(system:string_chars(_, _)).
  644safe_primitive(system:string_codes(_, _)).
  645safe_primitive(system:string_code(_,_,_)).
  646safe_primitive(system:sub_string(_,_,_,_,_)).
  647safe_primitive(system:split_string(_,_,_,_)).
  648safe_primitive(system:atomics_to_string(_,_,_)).
  649safe_primitive(system:atomics_to_string(_,_)).
  650safe_primitive(system:string_concat(_,_,_)).
  651safe_primitive(system:string_length(_,_)).
  652safe_primitive(system:string_lower(_,_)).
  653safe_primitive(system:string_upper(_,_)).
  654safe_primitive(system:term_string(_,_)).
  655safe_primitive('$syspreds':term_string(_,_,_)).
  656                                        % Lists
  657safe_primitive(length(_,_)).
  658                                        % exceptions
  659safe_primitive(throw(_)).
  660safe_primitive(system:abort).
  661                                        % misc
  662safe_primitive(current_prolog_flag(_,_)).
  663safe_primitive(current_op(_,_,_)).
  664safe_primitive(system:sleep(_)).
  665safe_primitive(system:thread_self(_)).
  666safe_primitive(system:get_time(_)).
  667safe_primitive(system:statistics(_,_)).
  668:- if(current_prolog_flag(threads,true)).  669safe_primitive(system:thread_statistics(Id,_,_)) :-
  670    (   var(Id)
  671    ->  instantiation_error(Id)
  672    ;   thread_self(Id)
  673    ).
  674safe_primitive(system:thread_property(Id,_)) :-
  675    (   var(Id)
  676    ->  instantiation_error(Id)
  677    ;   thread_self(Id)
  678    ).
  679:- endif.  680safe_primitive(system:format_time(_,_,_)).
  681safe_primitive(system:format_time(_,_,_,_)).
  682safe_primitive(system:date_time_stamp(_,_)).
  683safe_primitive(system:stamp_date_time(_,_,_)).
  684safe_primitive(system:strip_module(_,_,_)).
  685safe_primitive('$messages':message_to_string(_,_)).
  686safe_primitive(system:import_module(_,_)).
  687safe_primitive(system:file_base_name(_,_)).
  688safe_primitive(system:file_directory_name(_,_)).
  689safe_primitive(system:file_name_extension(_,_,_)).
  690
  691safe_primitive(clause(H,_)) :- safe_clause(H).
  692safe_primitive(asserta(X)) :- safe_assert(X).
  693safe_primitive(assertz(X)) :- safe_assert(X).
  694safe_primitive(retract(X)) :- safe_assert(X).
  695safe_primitive(retractall(X)) :- safe_assert(X).
  696safe_primitive('$dcg':dcg_translate_rule(_,_)).
  697safe_primitive('$syspreds':predicate_property(Pred, _)) :-
  698    nonvar(Pred),
  699    Pred \= (_:_).
  700
  701% We need to do data flow analysis to find the tag of the
  702% target key before we can conclude that functions on dicts
  703% are safe.
  704safe_primitive('$dicts':'.'(_,K,_)) :- atom(K).
  705safe_primitive('$dicts':'.'(_,K,_)) :-
  706    (   nonvar(K)
  707    ->  dict_built_in(K)
  708    ;   instantiation_error(K)
  709    ).
  710
  711dict_built_in(get(_)).
  712dict_built_in(put(_)).
  713dict_built_in(put(_,_)).
  714
  715% The non-ISO system predicates.  These can be redefined, so we must
  716% be careful to ensure the system ones are used.
  717
  718safe_primitive(system:false).
  719safe_primitive(system:cyclic_term(_)).
  720safe_primitive(system:msort(_,_)).
  721safe_primitive(system:sort(_,_,_,_)).
  722safe_primitive(system:between(_,_,_)).
  723safe_primitive(system:succ(_,_)).
  724safe_primitive(system:plus(_,_,_)).
  725safe_primitive(system:float_class(_,_)).
  726safe_primitive(system:term_variables(_,_)).
  727safe_primitive(system:term_variables(_,_,_)).
  728safe_primitive(system:'$term_size'(_,_,_)).
  729safe_primitive(system:atom_to_term(_,_,_)).
  730safe_primitive(system:term_to_atom(_,_)).
  731safe_primitive(system:atomic_list_concat(_,_,_)).
  732safe_primitive(system:atomic_list_concat(_,_)).
  733safe_primitive(system:downcase_atom(_,_)).
  734safe_primitive(system:upcase_atom(_,_)).
  735safe_primitive(system:is_list(_)).
  736safe_primitive(system:memberchk(_,_)).
  737safe_primitive(system:'$skip_list'(_,_,_)).
  738safe_primitive(system:'$seek_list'(_, _, _, _)).
  739                                        % attributes
  740safe_primitive(system:get_attr(_,_,_)).
  741safe_primitive(system:get_attrs(_,_)).
  742safe_primitive(system:term_attvars(_,_)).
  743safe_primitive(system:del_attr(_,_)).
  744safe_primitive(system:del_attrs(_)).
  745safe_primitive('$attvar':copy_term(_,_,_)).
  746                                        % globals
  747safe_primitive(system:b_getval(_,_)).
  748safe_primitive(system:b_setval(Var,_)) :-
  749    safe_global_var(Var).
  750safe_primitive(system:nb_getval(_,_)).
  751safe_primitive('$syspreds':nb_setval(Var,_)) :-
  752    safe_global_var(Var).
  753safe_primitive(system:nb_linkval(Var,_)) :-
  754    safe_global_var(Var).
  755safe_primitive(system:nb_current(_,_)).
  756                                        % database
  757safe_primitive(system:assert(X)) :-
  758    safe_assert(X).
  759                                        % Output
  760safe_primitive(system:writeln(_)).
  761safe_primitive('$messages':print_message(_,_)).
  762
  763                                        % Stack limits (down)
  764safe_primitive('$syspreds':set_prolog_stack(Stack, limit(ByteExpr))) :-
  765    nonvar(Stack),
  766    stack_name(Stack),
  767    catch(Bytes is ByteExpr, _, fail),
  768    prolog_stack_property(Stack, limit(Current)),
  769    Bytes =< Current.
  770
  771stack_name(global).
  772stack_name(local).
  773stack_name(trail).
  774
  775safe_primitive('$tabling':abolish_all_tables).
  776safe_primitive('$tabling':'$wrap_tabled'(Module:_Head, _Mode)) :-
  777    prolog_load_context(module, Module),
  778    !.
  779safe_primitive('$tabling':'$moded_wrap_tabled'(Module:_Head,_,_,_,_)) :-
  780    prolog_load_context(module, Module),
  781    !.
  782
  783
  784% use_module/1.  We only allow for .pl files that are loaded from
  785% relative paths that do not contain /../
  786
  787safe_primitive(system:use_module(Spec, _Import)) :-
  788    safe_primitive(system:use_module(Spec)).
  789safe_primitive(system:load_files(Spec, Options)) :-
  790    safe_primitive(system:use_module(Spec)),
  791    maplist(safe_load_file_option, Options).
  792safe_primitive(system:use_module(Spec)) :-
  793    ground(Spec),
  794    (   atom(Spec)
  795    ->  Path = Spec
  796    ;   Spec =.. [_Alias, Segments],
  797        phrase(segments_to_path(Segments), List),
  798        atomic_list_concat(List, Path)
  799    ),
  800    \+ is_absolute_file_name(Path),
  801    \+ sub_atom(Path, _, _, _, '/../'),
  802    absolute_file_name(Spec, AbsFile,
  803                       [ access(read),
  804                         file_type(prolog),
  805                         file_errors(fail)
  806                       ]),
  807    file_name_extension(_, Ext, AbsFile),
  808    save_extension(Ext).
  809
  810% support predicates for safe_primitive, validating the safety of
  811% arguments to certain goals.
  812
  813segments_to_path(A/B) -->
  814    !,
  815    segments_to_path(A),
  816    [/],
  817    segments_to_path(B).
  818segments_to_path(X) -->
  819    [X].
  820
  821save_extension(pl).
  822
  823safe_load_file_option(if(changed)).
  824safe_load_file_option(if(not_loaded)).
  825safe_load_file_option(must_be_module(_)).
  826safe_load_file_option(optimise(_)).
  827safe_load_file_option(silent(_)).
  828
  829%!  safe_assert(+Term) is semidet.
  830%
  831%   True if assert(Term) is safe,  which   means  it  asserts in the
  832%   current module. Cross-module asserts are   considered unsafe. We
  833%   only allow for adding facts. In theory,  we could also allow for
  834%   rules if we prove the safety of the body.
  835
  836safe_assert(C) :- cyclic_term(C), !, fail.
  837safe_assert(X) :- var(X), !, fail.
  838safe_assert(_Head:-_Body) :- !, fail.
  839safe_assert(_:_) :- !, fail.
  840safe_assert(_).
  841
  842%!  safe_clause(+Head) is semidet.
  843%
  844%   Consider a call to clause safe if  it   does  not try to cross a
  845%   module boundary. Cross-module usage  of   clause/2  can  extract
  846%   private information from other modules.
  847
  848safe_clause(H) :- var(H), !.
  849safe_clause(_:_) :- !, fail.
  850safe_clause(_).
  851
  852
  853%!  safe_global_var(+Name) is semidet.
  854%
  855%   True if Name  is  a  global   variable  to  which  assertion  is
  856%   considered safe.
  857
  858safe_global_var(Name) :-
  859    var(Name),
  860    !,
  861    instantiation_error(Name).
  862safe_global_var(Name) :-
  863    safe_global_variable(Name).
  864
  865%!  safe_global_variable(Name) is semidet.
  866%
  867%   Declare the given global variable safe to write to.
  868
  869
  870%!  safe_meta(+Goal, -Called:list(callable)) is semidet.
  871%
  872%   Hook. True if Goal is a   meta-predicate that is considered safe
  873%   iff all elements in Called are safe.
  874
  875safe_meta(system:put_attr(V,M,A), Called) :-
  876    !,
  877    (   atom(M)
  878    ->  attr_hook_predicates([ attr_unify_hook(A, _),
  879                               attribute_goals(V,_,_),
  880                               project_attributes(_,_)
  881                             ], M, Called)
  882    ;   instantiation_error(M)
  883    ).
  884safe_meta(system:with_output_to(Output, G), [G]) :-
  885    safe_output(Output),
  886    !.
  887safe_meta(system:format(Format, Args), Calls) :-
  888    format_calls(Format, Args, Calls).
  889safe_meta(system:format(Output, Format, Args), Calls) :-
  890    safe_output(Output),
  891    format_calls(Format, Args, Calls).
  892safe_meta(prolog_debug:debug(_Term, Format, Args), Calls) :-
  893    format_calls(Format, Args, Calls).
  894safe_meta(system:set_prolog_flag(Flag, Value), []) :-
  895    atom(Flag),
  896    safe_prolog_flag(Flag, Value).
  897safe_meta('$attvar':freeze(_Var,Goal), [Goal]).
  898safe_meta(phrase(NT,Xs0,Xs), [Goal]) :- % phrase/2,3 and call_dcg/2,3
  899    expand_nt(NT,Xs0,Xs,Goal).
  900safe_meta(phrase(NT,Xs0), [Goal]) :-
  901    expand_nt(NT,Xs0,[],Goal).
  902safe_meta('$dcg':call_dcg(NT,Xs0,Xs), [Goal]) :-
  903    expand_nt(NT,Xs0,Xs,Goal).
  904safe_meta('$dcg':call_dcg(NT,Xs0), [Goal]) :-
  905    expand_nt(NT,Xs0,[],Goal).
  906safe_meta('$tabling':abolish_table_subgoals(V), []) :-
  907    \+ qualified(V).
  908safe_meta('$tabling':current_table(V, _), []) :-
  909    \+ qualified(V).
  910safe_meta('$tabling':tnot(G), [G]).
  911safe_meta('$tabling':not_exists(G), [G]).
  912
  913qualified(V) :-
  914    nonvar(V),
  915    V = _:_.
  916
  917%!  attr_hook_predicates(+Hooks0, +Module, -Hooks) is det.
  918%
  919%   Filter the defined hook implementations.   This  is safe because
  920%   (1) calling an undefined predicate is   not  a safety issue, (2)
  921%   the  user  an  only  assert  in  the  current  module  and  only
  922%   predicates that have a safe body. This avoids the need to define
  923%   attribute hooks solely for the purpose of making them safe.
  924
  925attr_hook_predicates([], _, []).
  926attr_hook_predicates([H|T], M, Called) :-
  927    (   predicate_property(M:H, defined)
  928    ->  Called = [M:H|Rest]
  929    ;   Called = Rest
  930    ),
  931    attr_hook_predicates(T, M, Rest).
  932
  933
  934%!  expand_nt(+NT, ?Xs0, ?Xs, -NewGoal)
  935%
  936%   Similar to expand_phrase/2, but we do   throw  errors instead of
  937%   failing if NT is not sufficiently instantiated.
  938
  939expand_nt(NT, _Xs0, _Xs, _NewGoal) :-
  940    strip_module(NT, _, Plain),
  941    var(Plain),
  942    !,
  943    instantiation_error(Plain).
  944expand_nt(NT, Xs0, Xs, NewGoal) :-
  945    dcg_translate_rule((pseudo_nt --> NT),
  946                       (pseudo_nt(Xs0c,Xsc) :- NewGoal0)),
  947    (   var(Xsc), Xsc \== Xs0c
  948    ->  Xs = Xsc, NewGoal1 = NewGoal0
  949    ;   NewGoal1 = (NewGoal0, Xsc = Xs)
  950    ),
  951    (   var(Xs0c)
  952    ->  Xs0 = Xs0c,
  953        NewGoal = NewGoal1
  954    ;   NewGoal = ( Xs0 = Xs0c, NewGoal1 )
  955    ).
  956
  957%!  safe_meta_call(+Goal, +Context, -Called:list(callable)) is semidet.
  958%
  959%   True if Goal is a   meta-predicate that is considered safe
  960%   iff all elements in Called are safe.
  961
  962safe_meta_call(Goal, _, _Called) :-
  963    debug(sandbox(meta), 'Safe meta ~p?', [Goal]),
  964    fail.
  965safe_meta_call(Goal, Context, Called) :-
  966    (   safe_meta(Goal, Called)
  967    ->  true
  968    ;   safe_meta(Goal, Context, Called)
  969    ),
  970    !.     % call hook
  971safe_meta_call(Goal, _, Called) :-
  972    Goal = M:Plain,
  973    compound(Plain),
  974    compound_name_arity(Plain, Name, Arity),
  975    safe_meta_predicate(M:Name/Arity),
  976    predicate_property(Goal, meta_predicate(Spec)),
  977    !,
  978    called(Spec, Plain, Called).
  979safe_meta_call(M:Goal, _, Called) :-
  980    !,
  981    generic_goal(Goal, Gen),
  982    safe_meta(M:Gen),
  983    called(Gen, Goal, Called).
  984safe_meta_call(Goal, _, Called) :-
  985    generic_goal(Goal, Gen),
  986    safe_meta(Gen),
  987    called(Gen, Goal, Called).
  988
  989called(Gen, Goal, Called) :-
  990    compound_name_arity(Goal, _, Arity),
  991    called(1, Arity, Gen, Goal, Called).
  992
  993called(I, Arity, Gen, Goal, Called) :-
  994    I =< Arity,
  995    !,
  996    arg(I, Gen, Spec),
  997    (   calling_meta_spec(Spec)
  998    ->  arg(I, Goal, Called0),
  999        extend(Spec, Called0, G),
 1000        Called = [G|Rest]
 1001    ;   Called = Rest
 1002    ),
 1003    I2 is I+1,
 1004    called(I2, Arity, Gen, Goal, Rest).
 1005called(_, _, _, _, []).
 1006
 1007generic_goal(G, Gen) :-
 1008    functor(G, Name, Arity),
 1009    functor(Gen, Name, Arity).
 1010
 1011calling_meta_spec(V) :- var(V), !, fail.
 1012calling_meta_spec(I) :- integer(I), !.
 1013calling_meta_spec(^).
 1014calling_meta_spec(//).
 1015
 1016
 1017extend(^, G, Plain) :-
 1018    !,
 1019    strip_existential(G, Plain).
 1020extend(//, DCG, Goal) :-
 1021    !,
 1022    (   expand_phrase(call_dcg(DCG,_,_), Goal)
 1023    ->  true
 1024    ;   instantiation_error(DCG)    % Ask more instantiation.
 1025    ).                              % might not help, but does not harm.
 1026extend(0, G, G) :- !.
 1027extend(I, M:G0, M:G) :-
 1028    !,
 1029    G0 =.. List,
 1030    length(Extra, I),
 1031    append(List, Extra, All),
 1032    G =.. All.
 1033extend(I, G0, G) :-
 1034    G0 =.. List,
 1035    length(Extra, I),
 1036    append(List, Extra, All),
 1037    G =.. All.
 1038
 1039strip_existential(Var, Var) :-
 1040    var(Var),
 1041    !.
 1042strip_existential(M:G0, M:G) :-
 1043    !,
 1044    strip_existential(G0, G).
 1045strip_existential(_^G0, G) :-
 1046    !,
 1047    strip_existential(G0, G).
 1048strip_existential(G, G).
 1049
 1050%!  safe_meta(?Template).
 1051
 1052safe_meta((0,0)).
 1053safe_meta((0;0)).
 1054safe_meta((0->0)).
 1055safe_meta(system:(0*->0)).
 1056safe_meta(catch(0,*,0)).
 1057safe_meta(findall(*,0,*)).
 1058safe_meta('$bags':findall(*,0,*,*)).
 1059safe_meta(setof(*,^,*)).
 1060safe_meta(bagof(*,^,*)).
 1061safe_meta('$bags':findnsols(*,*,0,*)).
 1062safe_meta('$bags':findnsols(*,*,0,*,*)).
 1063safe_meta(system:call_cleanup(0,0)).
 1064safe_meta(system:setup_call_cleanup(0,0,0)).
 1065safe_meta(system:setup_call_catcher_cleanup(0,0,*,0)).
 1066safe_meta('$attvar':call_residue_vars(0,*)).
 1067safe_meta('$syspreds':call_with_inference_limit(0,*,*)).
 1068safe_meta('$syspreds':call_with_depth_limit(0,*,*)).
 1069safe_meta('$syspreds':undo(0)).
 1070safe_meta(^(*,0)).
 1071safe_meta(\+(0)).
 1072safe_meta(call(0)).
 1073safe_meta(call(1,*)).
 1074safe_meta(call(2,*,*)).
 1075safe_meta(call(3,*,*,*)).
 1076safe_meta(call(4,*,*,*,*)).
 1077safe_meta(call(5,*,*,*,*,*)).
 1078safe_meta(call(6,*,*,*,*,*,*)).
 1079safe_meta('$tabling':start_tabling(*,0)).
 1080safe_meta('$tabling':start_tabling(*,0,*,*)).
 1081safe_meta(wfs:call_delays(0,*)).
 1082
 1083%!  safe_output(+Output)
 1084%
 1085%   True if something is a safe output argument for with_output_to/2
 1086%   and friends. We do not want writing to streams.
 1087
 1088safe_output(Output) :-
 1089    var(Output),
 1090    !,
 1091    instantiation_error(Output).
 1092safe_output(atom(_)).
 1093safe_output(string(_)).
 1094safe_output(codes(_)).
 1095safe_output(codes(_,_)).
 1096safe_output(chars(_)).
 1097safe_output(chars(_,_)).
 1098safe_output(current_output).
 1099safe_output(current_error).
 1100
 1101%!  format_calls(+Format, +FormatArgs, -Calls)
 1102%
 1103%   Find ~@ calls from Format and Args.
 1104
 1105:- public format_calls/3.                       % used in pengines_io
 1106
 1107format_calls(Format, Args, Calls) :-
 1108    is_list(Args),
 1109    !,
 1110    format_types(Format, Types),
 1111    (   format_callables(Types, Args, Calls)
 1112    ->  true
 1113    ;   throw(error(format_error(Format, Types, Args), _))
 1114    ).
 1115format_calls(Format, Arg, Calls) :-
 1116    format_calls(Format, [Arg], Calls).
 1117
 1118format_callables([], [], []).
 1119format_callables([callable|TT], [G|TA], [G|TG]) :-
 1120    !,
 1121    format_callables(TT, TA, TG).
 1122format_callables([_|TT], [_|TA], TG) :-
 1123    !,
 1124    format_callables(TT, TA, TG).
 1125
 1126
 1127                 /*******************************
 1128                 *    SAFE COMPILATION HOOKS    *
 1129                 *******************************/
 1130
 1131:- multifile
 1132    prolog:sandbox_allowed_directive/1,
 1133    prolog:sandbox_allowed_goal/1,
 1134    prolog:sandbox_allowed_expansion/1. 1135
 1136%!  prolog:sandbox_allowed_directive(:G) is det.
 1137%
 1138%   Throws an exception if G is not considered a safe directive.
 1139
 1140prolog:sandbox_allowed_directive(Directive) :-
 1141    debug(sandbox(directive), 'Directive: ~p', [Directive]),
 1142    fail.
 1143prolog:sandbox_allowed_directive(Directive) :-
 1144    safe_directive(Directive),
 1145    !.
 1146prolog:sandbox_allowed_directive(M:PredAttr) :-
 1147    \+ prolog_load_context(module, M),
 1148    !,
 1149    debug(sandbox(directive), 'Cross-module directive', []),
 1150    permission_error(execute, sandboxed_directive, (:- M:PredAttr)).
 1151prolog:sandbox_allowed_directive(M:PredAttr) :-
 1152    safe_pattr(PredAttr),
 1153    !,
 1154    PredAttr =.. [Attr, Preds],
 1155    (   safe_pattr(Preds, Attr)
 1156    ->  true
 1157    ;   permission_error(execute, sandboxed_directive, (:- M:PredAttr))
 1158    ).
 1159prolog:sandbox_allowed_directive(_:Directive) :-
 1160    safe_source_directive(Directive),
 1161    !.
 1162prolog:sandbox_allowed_directive(_:Directive) :-
 1163    directive_loads_file(Directive, File),
 1164    !,
 1165    safe_path(File).
 1166prolog:sandbox_allowed_directive(G) :-
 1167    safe_goal(G).
 1168
 1169%!  safe_directive(:Directive) is semidet.
 1170%
 1171%   Hook to declare additional directives as safe. The argument is a
 1172%   term `Module:Directive` (without =|:-|= wrapper).  In almost all
 1173%   cases, the implementation must verify that   the `Module` is the
 1174%   current load context as illustrated  below.   This  check is not
 1175%   performed by the system to  allow   for  cases  where particular
 1176%   cross-module directives are allowed.
 1177%
 1178%     ==
 1179%     sandbox:safe_directive(M:Directive) :-
 1180%         prolog_load_context(module, M),
 1181%         ...
 1182%     ==
 1183
 1184
 1185safe_pattr(dynamic(_)).
 1186safe_pattr(thread_local(_)).
 1187safe_pattr(volatile(_)).
 1188safe_pattr(discontiguous(_)).
 1189safe_pattr(multifile(_)).
 1190safe_pattr(public(_)).
 1191safe_pattr(meta_predicate(_)).
 1192safe_pattr(table(_)).
 1193safe_pattr(non_terminal(_)).
 1194
 1195safe_pattr(Var, _) :-
 1196    var(Var),
 1197    !,
 1198    instantiation_error(Var).
 1199safe_pattr((A,B), Attr) :-
 1200    !,
 1201    safe_pattr(A, Attr),
 1202    safe_pattr(B, Attr).
 1203safe_pattr(M:G, Attr) :-
 1204    !,
 1205    (   atom(M),
 1206        prolog_load_context(module, M)
 1207    ->  true
 1208    ;   Goal =.. [Attr,M:G],
 1209        permission_error(directive, sandboxed, (:- Goal))
 1210    ).
 1211safe_pattr(_, _).
 1212
 1213safe_source_directive(op(_,_,Name)) :-
 1214    !,
 1215    (   atom(Name)
 1216    ->  true
 1217    ;   is_list(Name),
 1218        maplist(atom, Name)
 1219    ).
 1220safe_source_directive(set_prolog_flag(Flag, Value)) :-
 1221    !,
 1222    atom(Flag), ground(Value),
 1223    safe_prolog_flag(Flag, Value).
 1224safe_source_directive(style_check(_)).
 1225safe_source_directive(initialization(_)).   % Checked at runtime
 1226safe_source_directive(initialization(_,_)). % Checked at runtime
 1227
 1228directive_loads_file(use_module(library(X)), X).
 1229directive_loads_file(use_module(library(X), _Imports), X).
 1230directive_loads_file(load_files(library(X), _Options), X).
 1231directive_loads_file(ensure_loaded(library(X)), X).
 1232directive_loads_file(include(X), X).
 1233
 1234safe_path(X) :-
 1235    var(X),
 1236    !,
 1237    instantiation_error(X).
 1238safe_path(X) :-
 1239    (   atom(X)
 1240    ;   string(X)
 1241    ),
 1242    !,
 1243    \+ sub_atom(X, 0, _, 0, '..'),
 1244    \+ sub_atom(X, 0, _, _, '/'),
 1245    \+ sub_atom(X, 0, _, _, '../'),
 1246    \+ sub_atom(X, _, _, 0, '/..'),
 1247    \+ sub_atom(X, _, _, _, '/../').
 1248safe_path(A/B) :-
 1249    !,
 1250    safe_path(A),
 1251    safe_path(B).
 1252
 1253
 1254%!  safe_prolog_flag(+Flag, +Value) is det.
 1255%
 1256%   True if it is safe to set the flag Flag to Value.
 1257%
 1258%   @tbd    If we can avoid that files are loaded after changing
 1259%           this flag, we can allow for more flags.  The syntax
 1260%           flags are safe because they are registered with the
 1261%           module.
 1262
 1263% misc
 1264safe_prolog_flag(generate_debug_info, _).
 1265safe_prolog_flag(optimise, _).
 1266safe_prolog_flag(occurs_check, _).
 1267safe_prolog_flag(write_attributes, _).
 1268% syntax
 1269safe_prolog_flag(var_prefix, _).
 1270safe_prolog_flag(double_quotes, _).
 1271safe_prolog_flag(back_quotes, _).
 1272safe_prolog_flag(rational_syntax, _).
 1273% arithmetic
 1274safe_prolog_flag(prefer_rationals, _).
 1275safe_prolog_flag(float_overflow, _).
 1276safe_prolog_flag(float_zero_div, _).
 1277safe_prolog_flag(float_undefined, _).
 1278safe_prolog_flag(float_underflow, _).
 1279safe_prolog_flag(float_rounding, _).
 1280safe_prolog_flag(float_rounding, _).
 1281safe_prolog_flag(max_rational_size, _).
 1282safe_prolog_flag(max_rational_size_action, _).
 1283% tabling
 1284safe_prolog_flag(max_answers_for_subgoal,_).
 1285safe_prolog_flag(max_answers_for_subgoal_action,_).
 1286safe_prolog_flag(max_table_answer_size,_).
 1287safe_prolog_flag(max_table_answer_size_action,_).
 1288safe_prolog_flag(max_table_subgoal_size,_).
 1289safe_prolog_flag(max_table_subgoal_size_action,_).
 1290
 1291
 1292%!  prolog:sandbox_allowed_expansion(:G) is det.
 1293%
 1294%   Throws an exception if G  is   not  considered  a safe expansion
 1295%   goal. This deals with call-backs from the compiler for
 1296%
 1297%     - goal_expansion/2
 1298%     - term_expansion/2
 1299%     - Quasi quotations.
 1300%
 1301%   Our assumption is that external expansion rules are coded safely
 1302%   and we only need to be  careful   if  the sandboxed code defines
 1303%   expansion rules.
 1304
 1305prolog:sandbox_allowed_expansion(M:G) :-
 1306    prolog_load_context(module, M),
 1307    !,
 1308    debug(sandbox(expansion), 'Expand in ~p: ~p', [M, G]),
 1309    safe_goal(M:G).
 1310prolog:sandbox_allowed_expansion(_,_).
 1311
 1312%!  prolog:sandbox_allowed_goal(:G) is det.
 1313%
 1314%   Throw an exception if it is not safe to call G
 1315
 1316prolog:sandbox_allowed_goal(G) :-
 1317    safe_goal(G).
 1318
 1319
 1320                 /*******************************
 1321                 *            MESSAGES          *
 1322                 *******************************/
 1323
 1324:- multifile
 1325    prolog:message//1,
 1326    prolog:message_context//1,
 1327    prolog:error_message//1. 1328
 1329prolog:message(error(instantiation_error, Context)) -->
 1330    { nonvar(Context),
 1331      Context = sandbox(_Goal,Parents),
 1332      numbervars(Context, 1, _)
 1333    },
 1334    [ 'Sandbox restriction!'-[], nl,
 1335      'Could not derive which predicate may be called from'-[]
 1336    ],
 1337    (   { Parents == [] }
 1338    ->  [ 'Search space too large'-[] ]
 1339    ;   callers(Parents, 10)
 1340    ).
 1341
 1342prolog:message_context(sandbox(_G, [])) --> !.
 1343prolog:message_context(sandbox(_G, Parents)) -->
 1344    [ nl, 'Reachable from:'-[] ],
 1345    callers(Parents, 10).
 1346
 1347callers([], _) --> !.
 1348callers(_,  0) --> !.
 1349callers([G|Parents], Level) -->
 1350    { NextLevel is Level-1
 1351    },
 1352    [ nl, '\t  ~p'-[G] ],
 1353    callers(Parents, NextLevel).
 1354
 1355prolog:message(bad_safe_declaration(Goal, File, Line)) -->
 1356    [ '~w:~d: Invalid safe_primitive/1 declaration: ~p'-
 1357      [File, Line, Goal] ].
 1358
 1359prolog:error_message(format_error(Format, Types, Args)) -->
 1360    format_error(Format, Types, Args).
 1361
 1362format_error(Format, Types, Args) -->
 1363    { length(Types, TypeLen),
 1364      length(Args, ArgsLen),
 1365      (   TypeLen > ArgsLen
 1366      ->  Problem = 'not enough'
 1367      ;   Problem = 'too many'
 1368      )
 1369    },
 1370    [ 'format(~q): ~w arguments (found ~w, need ~w)'-
 1371      [Format, Problem, ArgsLen, TypeLen]
 1372    ]