Annotation of loncom/xml/Safe.pm, revision 1.4

1.1       albertel    1: package Safe;
                      2: 
                      3: use 5.003_11;
                      4: use strict;
1.2       albertel    5: use vars qw($VERSION);
1.1       albertel    6: 
1.4     ! albertel    7: $VERSION = "2.062";
1.1       albertel    8: 
                      9: use Carp;
                     10: 
                     11: use Opcode 1.01, qw(
                     12:     opset opset_to_ops opmask_add
                     13:     empty_opset full_opset invert_opset verify_opset
                     14:     opdesc opcodes opmask define_optag opset_to_hex
                     15: );
                     16: 
                     17: *ops_to_opset = \&opset;   # Temporary alias for old Penguins
                     18: 
                     19: 
                     20: my $default_root  = 0;
                     21: my $default_share = ['*_']; #, '*main::'];
                     22: 
                     23: sub new {
                     24:     my($class, $root, $mask) = @_;
                     25:     my $obj = {};
                     26:     bless $obj, $class;
                     27: 
                     28:     if (defined($root)) {
                     29: 	croak "Can't use \"$root\" as root name"
                     30: 	    if $root =~ /^main\b/ or $root !~ /^\w[:\w]*$/;
                     31: 	$obj->{Root}  = $root;
                     32: 	$obj->{Erase} = 0;
                     33:     }
                     34:     else {
                     35: 	$obj->{Root}  = "Safe::Root".$default_root++;
                     36: 	$obj->{Erase} = 1;
                     37:     }
                     38: 
                     39:     # use permit/deny methods instead till interface issues resolved
                     40:     # XXX perhaps new Safe 'Root', mask => $mask, foo => bar, ...;
                     41:     croak "Mask parameter to new no longer supported" if defined $mask;
                     42:     $obj->permit_only(':default');
                     43: 
                     44:     # We must share $_ and @_ with the compartment or else ops such
                     45:     # as split, length and so on won't default to $_ properly, nor
                     46:     # will passing argument to subroutines work (via @_). In fact,
                     47:     # for reasons I don't completely understand, we need to share
                     48:     # the whole glob *_ rather than $_ and @_ separately, otherwise
                     49:     # @_ in non default packages within the compartment don't work.
                     50:     $obj->share_from('main', $default_share);
                     51:     return $obj;
                     52: }
                     53: 
                     54: sub DESTROY {
                     55:     my $obj = shift;
                     56:     $obj->erase('DESTROY') if $obj->{Erase};
                     57: }
                     58: 
                     59: sub erase {
                     60:     my ($obj, $action) = @_;
                     61:     my $pkg = $obj->root();
                     62:     my ($stem, $leaf);
                     63: 
                     64:     no strict 'refs';
                     65:     $pkg = "main::$pkg\::";	# expand to full symbol table name
                     66:     ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
                     67: 
                     68:     # The 'my $foo' is needed! Without it you get an
                     69:     # 'Attempt to free unreferenced scalar' warning!
                     70:     my $stem_symtab = *{$stem}{HASH};
                     71: 
                     72:     #warn "erase($pkg) stem=$stem, leaf=$leaf";
                     73:     #warn " stem_symtab hash ".scalar(%$stem_symtab)."\n";
                     74: 	# ", join(', ', %$stem_symtab),"\n";
                     75: 
                     76: #    delete $stem_symtab->{$leaf};
                     77: 
                     78:     my $leaf_glob   = $stem_symtab->{$leaf};
                     79:     my $leaf_symtab = *{$leaf_glob}{HASH};
                     80: #    warn " leaf_symtab ", join(', ', %$leaf_symtab),"\n";
                     81:     %$leaf_symtab = ();
                     82:     #delete $leaf_symtab->{'__ANON__'};
                     83:     #delete $leaf_symtab->{'foo'};
                     84:     #delete $leaf_symtab->{'main::'};
                     85: #    my $foo = undef ${"$stem\::"}{"$leaf\::"};
                     86: 
                     87:     if ($action and $action eq 'DESTROY') {
                     88:         delete $stem_symtab->{$leaf};
                     89:     } else {
                     90:         $obj->share_from('main', $default_share);
                     91:     }
                     92:     1;
                     93: }
                     94: 
                     95: 
                     96: sub reinit {
                     97:     my $obj= shift;
                     98:     $obj->erase;
                     99:     $obj->share_redo;
                    100: }
                    101: 
                    102: sub root {
                    103:     my $obj = shift;
                    104:     croak("Safe root method now read-only") if @_;
                    105:     return $obj->{Root};
                    106: }
                    107: 
                    108: 
                    109: sub mask {
                    110:     my $obj = shift;
                    111:     return $obj->{Mask} unless @_;
                    112:     $obj->deny_only(@_);
                    113: }
                    114: 
                    115: # v1 compatibility methods
                    116: sub trap   { shift->deny(@_)   }
                    117: sub untrap { shift->permit(@_) }
                    118: 
                    119: sub deny {
                    120:     my $obj = shift;
                    121:     $obj->{Mask} |= opset(@_);
                    122: }
                    123: sub deny_only {
                    124:     my $obj = shift;
                    125:     $obj->{Mask} = opset(@_);
                    126: }
                    127: 
                    128: sub permit {
                    129:     my $obj = shift;
                    130:     # XXX needs testing
                    131:     $obj->{Mask} &= invert_opset opset(@_);
                    132: }
                    133: sub permit_only {
                    134:     my $obj = shift;
                    135:     $obj->{Mask} = invert_opset opset(@_);
                    136: }
                    137: 
                    138: 
                    139: sub dump_mask {
                    140:     my $obj = shift;
                    141:     print opset_to_hex($obj->{Mask}),"\n";
                    142: }
                    143: 
                    144: 
                    145: 
                    146: sub share {
                    147:     my($obj, @vars) = @_;
                    148:     $obj->share_from(scalar(caller), \@vars);
                    149: }
                    150: 
                    151: sub share_from {
                    152:     my $obj = shift;
                    153:     my $pkg = shift;
                    154:     my $vars = shift;
                    155:     my $no_record = shift || 0;
                    156:     my $root = $obj->root();
                    157:     croak("vars not an array ref") unless ref $vars eq 'ARRAY';
                    158: 	no strict 'refs';
                    159:     # Check that 'from' package actually exists
                    160:     croak("Package \"$pkg\" does not exist")
                    161: 	unless keys %{"$pkg\::"};
                    162:     my $arg;
                    163:     foreach $arg (@$vars) {
                    164: 	# catch some $safe->share($var) errors:
                    165: 	croak("'$arg' not a valid symbol table name")
                    166: 	    unless $arg =~ /^[\$\@%*&]?\w[\w:]*$/
                    167: 	    	or $arg =~ /^\$\W$/;
                    168: 	my ($var, $type);
                    169: 	$type = $1 if ($var = $arg) =~ s/^(\W)//;
                    170: 	# warn "share_from $pkg $type $var";
                    171: 	*{$root."::$var"} = (!$type)       ? \&{$pkg."::$var"}
                    172: 			  : ($type eq '&') ? \&{$pkg."::$var"}
                    173: 			  : ($type eq '$') ? \${$pkg."::$var"}
                    174: 			  : ($type eq '@') ? \@{$pkg."::$var"}
                    175: 			  : ($type eq '%') ? \%{$pkg."::$var"}
                    176: 			  : ($type eq '*') ?  *{$pkg."::$var"}
                    177: 			  : croak(qq(Can't share "$type$var" of unknown type));
                    178:     }
                    179:     $obj->share_record($pkg, $vars) unless $no_record or !$vars;
                    180: }
                    181: 
                    182: sub share_record {
                    183:     my $obj = shift;
                    184:     my $pkg = shift;
                    185:     my $vars = shift;
                    186:     my $shares = \%{$obj->{Shares} ||= {}};
                    187:     # Record shares using keys of $obj->{Shares}. See reinit.
                    188:     @{$shares}{@$vars} = ($pkg) x @$vars if @$vars;
                    189: }
                    190: sub share_redo {
                    191:     my $obj = shift;
                    192:     my $shares = \%{$obj->{Shares} ||= {}};
                    193: 	my($var, $pkg);
                    194:     while(($var, $pkg) = each %$shares) {
                    195: 	# warn "share_redo $pkg\:: $var";
                    196: 	$obj->share_from($pkg,  [ $var ], 1);
                    197:     }
                    198: }
                    199: sub share_forget {
                    200:     delete shift->{Shares};
                    201: }
                    202: 
                    203: sub varglob {
                    204:     my ($obj, $var) = @_;
                    205:     no strict 'refs';
                    206:     return *{$obj->root()."::$var"};
                    207: }
                    208: 
                    209: 
                    210: sub reval {
                    211:     my ($obj, $__SAFE_LOCAL_expr, $strict) = @_;
                    212:     my $root = $obj->{Root};
                    213: 
                    214:     # Create anon sub ref in root of compartment.
                    215:     # Uses a closure (on $expr) to pass in the code to be executed.
                    216:     # (eval on one line to keep line numbers as expected by caller)
1.3       albertel  217:     my $evalcode = sprintf('package %s; sub { @_ = (); eval $__SAFE_LOCAL_expr; }', $root);
1.1       albertel  218:     my $evalsub;
                    219: 
                    220: 	if ($strict) { use strict; $evalsub = eval $evalcode; }
                    221: 	else         {  no strict; $evalsub = eval $evalcode; }
                    222: 
                    223:     return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
                    224: }
                    225: 
                    226: sub rdo {
                    227:     my ($obj, $file) = @_;
                    228:     my $root = $obj->{Root};
                    229: 
                    230:     my $evalsub = eval
1.3       albertel  231: 	      sprintf('package %s; sub { @_ = (); do $file }', $root);
1.1       albertel  232:     return Opcode::_safe_call_sv($root, $obj->{Mask}, $evalsub);
                    233: }
                    234: 
                    235: 
                    236: 1;
                    237: 
                    238: __END__
                    239: 
                    240: =head1 NAME
                    241: 
                    242: Safe - Compile and execute code in restricted compartments
                    243: 
                    244: =head1 SYNOPSIS
                    245: 
                    246:   use Safe;
                    247: 
                    248:   $compartment = new Safe;
                    249: 
                    250:   $compartment->permit(qw(time sort :browse));
                    251: 
                    252:   $result = $compartment->reval($unsafe_code);
                    253: 
                    254: =head1 DESCRIPTION
                    255: 
                    256: The Safe extension module allows the creation of compartments
                    257: in which perl code can be evaluated. Each compartment has
                    258: 
                    259: =over 8
                    260: 
                    261: =item a new namespace
                    262: 
                    263: The "root" of the namespace (i.e. "main::") is changed to a
                    264: different package and code evaluated in the compartment cannot
                    265: refer to variables outside this namespace, even with run-time
                    266: glob lookups and other tricks.
                    267: 
                    268: Code which is compiled outside the compartment can choose to place
                    269: variables into (or I<share> variables with) the compartment's namespace
                    270: and only that data will be visible to code evaluated in the
                    271: compartment.
                    272: 
                    273: By default, the only variables shared with compartments are the
                    274: "underscore" variables $_ and @_ (and, technically, the less frequently
                    275: used %_, the _ filehandle and so on). This is because otherwise perl
                    276: operators which default to $_ will not work and neither will the
                    277: assignment of arguments to @_ on subroutine entry.
                    278: 
                    279: =item an operator mask
                    280: 
                    281: Each compartment has an associated "operator mask". Recall that
                    282: perl code is compiled into an internal format before execution.
                    283: Evaluating perl code (e.g. via "eval" or "do 'file'") causes
                    284: the code to be compiled into an internal format and then,
                    285: provided there was no error in the compilation, executed.
                    286: Code evaluated in a compartment compiles subject to the
                    287: compartment's operator mask. Attempting to evaluate code in a
                    288: compartment which contains a masked operator will cause the
                    289: compilation to fail with an error. The code will not be executed.
                    290: 
                    291: The default operator mask for a newly created compartment is
                    292: the ':default' optag.
                    293: 
                    294: It is important that you read the Opcode(3) module documentation
                    295: for more information, especially for detailed definitions of opnames,
                    296: optags and opsets.
                    297: 
                    298: Since it is only at the compilation stage that the operator mask
                    299: applies, controlled access to potentially unsafe operations can
                    300: be achieved by having a handle to a wrapper subroutine (written
                    301: outside the compartment) placed into the compartment. For example,
                    302: 
                    303:     $cpt = new Safe;
                    304:     sub wrapper {
                    305:         # vet arguments and perform potentially unsafe operations
                    306:     }
                    307:     $cpt->share('&wrapper');
                    308: 
                    309: =back
                    310: 
                    311: 
                    312: =head1 WARNING
                    313: 
                    314: The authors make B<no warranty>, implied or otherwise, about the
                    315: suitability of this software for safety or security purposes.
                    316: 
                    317: The authors shall not in any case be liable for special, incidental,
                    318: consequential, indirect or other similar damages arising from the use
                    319: of this software.
                    320: 
                    321: Your mileage will vary. If in any doubt B<do not use it>.
                    322: 
                    323: 
                    324: =head2 RECENT CHANGES
                    325: 
                    326: The interface to the Safe module has changed quite dramatically since
                    327: version 1 (as supplied with Perl5.002). Study these pages carefully if
                    328: you have code written to use Safe version 1 because you will need to
                    329: makes changes.
                    330: 
                    331: 
                    332: =head2 Methods in class Safe
                    333: 
                    334: To create a new compartment, use
                    335: 
                    336:     $cpt = new Safe;
                    337: 
                    338: Optional argument is (NAMESPACE), where NAMESPACE is the root namespace
                    339: to use for the compartment (defaults to "Safe::Root0", incremented for
                    340: each new compartment).
                    341: 
                    342: Note that version 1.00 of the Safe module supported a second optional
                    343: parameter, MASK.  That functionality has been withdrawn pending deeper
                    344: consideration. Use the permit and deny methods described below.
                    345: 
                    346: The following methods can then be used on the compartment
                    347: object returned by the above constructor. The object argument
                    348: is implicit in each case.
                    349: 
                    350: 
                    351: =over 8
                    352: 
                    353: =item permit (OP, ...)
                    354: 
                    355: Permit the listed operators to be used when compiling code in the
                    356: compartment (in I<addition> to any operators already permitted).
                    357: 
                    358: =item permit_only (OP, ...)
                    359: 
                    360: Permit I<only> the listed operators to be used when compiling code in
                    361: the compartment (I<no> other operators are permitted).
                    362: 
                    363: =item deny (OP, ...)
                    364: 
                    365: Deny the listed operators from being used when compiling code in the
                    366: compartment (other operators may still be permitted).
                    367: 
                    368: =item deny_only (OP, ...)
                    369: 
                    370: Deny I<only> the listed operators from being used when compiling code
                    371: in the compartment (I<all> other operators will be permitted).
                    372: 
                    373: =item trap (OP, ...)
                    374: 
                    375: =item untrap (OP, ...)
                    376: 
                    377: The trap and untrap methods are synonyms for deny and permit
                    378: respectfully.
                    379: 
                    380: =item share (NAME, ...)
                    381: 
                    382: This shares the variable(s) in the argument list with the compartment.
                    383: This is almost identical to exporting variables using the L<Exporter(3)>
                    384: module.
                    385: 
                    386: Each NAME must be the B<name> of a variable, typically with the leading
                    387: type identifier included. A bareword is treated as a function name.
                    388: 
                    389: Examples of legal names are '$foo' for a scalar, '@foo' for an
                    390: array, '%foo' for a hash, '&foo' or 'foo' for a subroutine and '*foo'
                    391: for a glob (i.e.  all symbol table entries associated with "foo",
                    392: including scalar, array, hash, sub and filehandle).
                    393: 
                    394: Each NAME is assumed to be in the calling package. See share_from
                    395: for an alternative method (which share uses).
                    396: 
                    397: =item share_from (PACKAGE, ARRAYREF)
                    398: 
                    399: This method is similar to share() but allows you to explicitly name the
                    400: package that symbols should be shared from. The symbol names (including
                    401: type characters) are supplied as an array reference.
                    402: 
                    403:     $safe->share_from('main', [ '$foo', '%bar', 'func' ]);
                    404: 
                    405: 
                    406: =item varglob (VARNAME)
                    407: 
                    408: This returns a glob reference for the symbol table entry of VARNAME in
                    409: the package of the compartment. VARNAME must be the B<name> of a
                    410: variable without any leading type marker. For example,
                    411: 
                    412:     $cpt = new Safe 'Root';
                    413:     $Root::foo = "Hello world";
                    414:     # Equivalent version which doesn't need to know $cpt's package name:
                    415:     ${$cpt->varglob('foo')} = "Hello world";
                    416: 
                    417: 
                    418: =item reval (STRING)
                    419: 
                    420: This evaluates STRING as perl code inside the compartment.
                    421: 
                    422: The code can only see the compartment's namespace (as returned by the
                    423: B<root> method). The compartment's root package appears to be the
                    424: C<main::> package to the code inside the compartment.
                    425: 
                    426: Any attempt by the code in STRING to use an operator which is not permitted
                    427: by the compartment will cause an error (at run-time of the main program
                    428: but at compile-time for the code in STRING).  The error is of the form
                    429: "%s trapped by operation mask operation...".
                    430: 
                    431: If an operation is trapped in this way, then the code in STRING will
                    432: not be executed. If such a trapped operation occurs or any other
                    433: compile-time or return error, then $@ is set to the error message, just
                    434: as with an eval().
                    435: 
                    436: If there is no error, then the method returns the value of the last
                    437: expression evaluated, or a return statement may be used, just as with
                    438: subroutines and B<eval()>. The context (list or scalar) is determined
                    439: by the caller as usual.
                    440: 
                    441: This behaviour differs from the beta distribution of the Safe extension
                    442: where earlier versions of perl made it hard to mimic the return
                    443: behaviour of the eval() command and the context was always scalar.
                    444: 
                    445: Some points to note:
                    446: 
                    447: If the entereval op is permitted then the code can use eval "..." to
                    448: 'hide' code which might use denied ops. This is not a major problem
                    449: since when the code tries to execute the eval it will fail because the
                    450: opmask is still in effect. However this technique would allow clever,
                    451: and possibly harmful, code to 'probe' the boundaries of what is
                    452: possible.
                    453: 
                    454: Any string eval which is executed by code executing in a compartment,
                    455: or by code called from code executing in a compartment, will be eval'd
                    456: in the namespace of the compartment. This is potentially a serious
                    457: problem.
                    458: 
                    459: Consider a function foo() in package pkg compiled outside a compartment
                    460: but shared with it. Assume the compartment has a root package called
                    461: 'Root'. If foo() contains an eval statement like eval '$foo = 1' then,
                    462: normally, $pkg::foo will be set to 1.  If foo() is called from the
                    463: compartment (by whatever means) then instead of setting $pkg::foo, the
                    464: eval will actually set $Root::pkg::foo.
                    465: 
                    466: This can easily be demonstrated by using a module, such as the Socket
                    467: module, which uses eval "..." as part of an AUTOLOAD function. You can
                    468: 'use' the module outside the compartment and share an (autoloaded)
                    469: function with the compartment. If an autoload is triggered by code in
                    470: the compartment, or by any code anywhere that is called by any means
                    471: from the compartment, then the eval in the Socket module's AUTOLOAD
                    472: function happens in the namespace of the compartment. Any variables
                    473: created or used by the eval'd code are now under the control of
                    474: the code in the compartment.
                    475: 
                    476: A similar effect applies to I<all> runtime symbol lookups in code
                    477: called from a compartment but not compiled within it.
                    478: 
                    479: 
                    480: 
                    481: =item rdo (FILENAME)
                    482: 
                    483: This evaluates the contents of file FILENAME inside the compartment.
                    484: See above documentation on the B<reval> method for further details.
                    485: 
                    486: =item root (NAMESPACE)
                    487: 
                    488: This method returns the name of the package that is the root of the
                    489: compartment's namespace.
                    490: 
                    491: Note that this behaviour differs from version 1.00 of the Safe module
                    492: where the root module could be used to change the namespace. That
                    493: functionality has been withdrawn pending deeper consideration.
                    494: 
                    495: =item mask (MASK)
                    496: 
                    497: This is a get-or-set method for the compartment's operator mask.
                    498: 
                    499: With no MASK argument present, it returns the current operator mask of
                    500: the compartment.
                    501: 
                    502: With the MASK argument present, it sets the operator mask for the
                    503: compartment (equivalent to calling the deny_only method).
                    504: 
                    505: =back
                    506: 
                    507: 
                    508: =head2 Some Safety Issues
                    509: 
                    510: This section is currently just an outline of some of the things code in
                    511: a compartment might do (intentionally or unintentionally) which can
                    512: have an effect outside the compartment.
                    513: 
                    514: =over 8
                    515: 
                    516: =item Memory
                    517: 
                    518: Consuming all (or nearly all) available memory.
                    519: 
                    520: =item CPU
                    521: 
                    522: Causing infinite loops etc.
                    523: 
                    524: =item Snooping
                    525: 
                    526: Copying private information out of your system. Even something as
                    527: simple as your user name is of value to others. Much useful information
                    528: could be gleaned from your environment variables for example.
                    529: 
                    530: =item Signals
                    531: 
                    532: Causing signals (especially SIGFPE and SIGALARM) to affect your process.
                    533: 
                    534: Setting up a signal handler will need to be carefully considered
                    535: and controlled.  What mask is in effect when a signal handler
                    536: gets called?  If a user can get an imported function to get an
                    537: exception and call the user's signal handler, does that user's
                    538: restricted mask get re-instated before the handler is called?
                    539: Does an imported handler get called with its original mask or
                    540: the user's one?
                    541: 
                    542: =item State Changes
                    543: 
                    544: Ops such as chdir obviously effect the process as a whole and not just
                    545: the code in the compartment. Ops such as rand and srand have a similar
                    546: but more subtle effect.
                    547: 
                    548: =back
                    549: 
                    550: =head2 AUTHOR
                    551: 
                    552: Originally designed and implemented by Malcolm Beattie,
                    553: mbeattie@sable.ox.ac.uk.
                    554: 
                    555: Reworked to use the Opcode module and other changes added by Tim Bunce
                    556: E<lt>F<Tim.Bunce@ig.co.uk>E<gt>.
                    557: 
                    558: =cut
                    559: 

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