[ViewVC] Diff of: cvs/CBOR-XS/XS.pm

Comparing CBOR-XS/XS.pm (file contents):
Revision 1.64 by root, Fri Nov 25 23:37:27 2016 UTC vs.
Revision 1.65 by root, Sat Nov 26 00:47:02 2016 UTC

…		…
64		64
65	package CBOR::XS;	65	package CBOR::XS;
66		66
67	use common::sense;	67	use common::sense;
68		68
69	our $VERSION = 1.51;	69	our $VERSION = 1.6;
70	our @ISA = qw(Exporter);	70	our @ISA = qw(Exporter);
71		71
72	our @EXPORT = qw(encode_cbor decode_cbor);	72	our @EXPORT = qw(encode_cbor decode_cbor);
73		73
74	use Exporter;	74	use Exporter;
…		…
112		112
113	The mutators for flags all return the CBOR object again and thus calls can	113	The mutators for flags all return the CBOR object again and thus calls can
114	be chained:	114	be chained:
115		115
116	my $cbor = CBOR::XS->new->encode ({a => [1,2]});	116	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
		117
		118	=item $cbor = new_safe CBOR::XS
		119
		120	Create a new, safe/secure CBOR::XS object. This is similar to C<new>,
		121	but configures the coder object to be safe to use with untrusted
		122	data. Currently, this is equivalent to:
		123
		124	my $cbor = CBOR::XS
		125	->new
		126	->forbid_objects
		127	->filter (\&CBOR::XS::safe_filter)
		128	->max_size (1e8);
		129
		130	But is more future proof (it is better to crash because of a change than
		131	to be exploited in other ways).
		132
		133	=cut
		134
		135	sub new_safe {
		136	CBOR::XS
		137	->new
		138	->forbid_objects
		139	->filter (\&CBOR::XS::safe_filter)
		140	->max_size (1e8)
		141	}
117		142
118	=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])	143	=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])
119		144
120	=item $max_depth = $cbor->get_max_depth	145	=item $max_depth = $cbor->get_max_depth
121		146
…		…
137		162
138	Note that nesting is implemented by recursion in C. The default value has	163	Note that nesting is implemented by recursion in C. The default value has
139	been chosen to be as large as typical operating systems allow without	164	been chosen to be as large as typical operating systems allow without
140	crashing.	165	crashing.
141		166
142	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	167	See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
143		168
144	=item $cbor = $cbor->max_size ([$maximum_string_size])	169	=item $cbor = $cbor->max_size ([$maximum_string_size])
145		170
146	=item $max_size = $cbor->get_max_size	171	=item $max_size = $cbor->get_max_size
147		172
…		…
152	effect on C<encode> (yet).	177	effect on C<encode> (yet).
153		178
154	If no argument is given, the limit check will be deactivated (same as when	179	If no argument is given, the limit check will be deactivated (same as when
155	C<0> is specified).	180	C<0> is specified).
156		181
157	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	182	See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
158		183
159	=item $cbor = $cbor->allow_unknown ([$enable])	184	=item $cbor = $cbor->allow_unknown ([$enable])
160		185
161	=item $enabled = $cbor->get_allow_unknown	186	=item $enabled = $cbor->get_allow_unknown
162		187
…		…
226	throwing an error.	251	throwing an error.
227		252
228	This option does not affect C<encode> in any way - shared values and	253	This option does not affect C<encode> in any way - shared values and
229	references will always be encoded properly if present.	254	references will always be encoded properly if present.
230		255
		256	=item $cbor = $cbor->forbid_objects ([$enable])
		257
		258	=item $enabled = $cbor->get_forbid_objects
		259
		260	Disables the use of the object serialiser protocol.
		261
		262	If C<$enable> is true (or missing), then C<encode> will will throw an
		263	exception when it encounters perl objects that would be encoded using the
		264	perl-object tag (26). When C<decode> encounters such tags, it will fall
		265	back to the general filter/tagged logic as if this were an unknown tag (by
		266	default resulting in a C<CBOR::XC::Tagged> object).
		267
		268	If C<$enable> is false (the default), then C<encode> will use the
		269	L<Types::Serialiser> object serialisation protocol to serialise objects
		270	into perl-object tags, and C<decode> will do the same to decode such tags.
		271
		272	See L<SECURITY CONSIDERATIONS>, below, for more info on why forbidding this
		273	protocol can be useful.
		274
231	=item $cbor = $cbor->pack_strings ([$enable])	275	=item $cbor = $cbor->pack_strings ([$enable])
232		276
233	=item $enabled = $cbor->get_pack_strings	277	=item $enabled = $cbor->get_pack_strings
234		278
235	If C<$enable> is true (or missing), then C<encode> will try not to encode	279	If C<$enable> is true (or missing), then C<encode> will try not to encode
…		…
337	replace the tagged value in the decoded data structure, or no values,	381	replace the tagged value in the decoded data structure, or no values,
338	which will result in default handling, which currently means the decoder	382	which will result in default handling, which currently means the decoder
339	creates a C<CBOR::XS::Tagged> object to hold the tag and the value.	383	creates a C<CBOR::XS::Tagged> object to hold the tag and the value.
340		384
341	When the filter is cleared (the default state), the default filter	385	When the filter is cleared (the default state), the default filter
342	function, C<CBOR::XS::default_filter>, is used. This function simply looks	386	function, C<CBOR::XS::default_filter>, is used. This function simply
343	up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists it must be	387	looks up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists
344	a code reference that is called with tag and value, and is responsible for	388	it must be a code reference that is called with tag and value, and is
345	decoding the value. If no entry exists, it returns no values.	389	responsible for decoding the value. If no entry exists, it returns no
		390	values. C<CBOR::XS> provides a number of default filter functions already,
		391	the the C<%CBOR::XS::FILTER> hash can be freely extended with more.
		392
		393	C<CBOR::XS> additionally provides an alternative filter function that is
		394	supposed to be safe to use with untrusted data (which the default filter
		395	might not), called C<CBOR::XS::safe_filter>, which works the same as
		396	the C<default_filter> but uses the C<%CBOR::XS::SAFE_FILTER> variable
		397	instead. It is prepopulated with the tag decoding functions that are
		398	deemed safe (basically the same as C<%CBOR::XS::FILTER> without all
		399	the bignum tags), and can be extended by user code as wlel, although,
		400	obviously, one should be very careful about adding decoding functions
		401	here, since the expectation is that they are safe to use on untrusted
		402	data, after all.
346		403
347	Example: decode all tags not handled internally into C<CBOR::XS::Tagged>	404	Example: decode all tags not handled internally into C<CBOR::XS::Tagged>
348	objects, with no other special handling (useful when working with	405	objects, with no other special handling (useful when working with
349	potentially "unsafe" CBOR data).	406	potentially "unsafe" CBOR data).
350		407
…		…
356	$CBOR::XS::FILTER{1347375694} = sub {	413	$CBOR::XS::FILTER{1347375694} = sub {
357	my ($tag, $value);	414	my ($tag, $value);
358		415
359	"tag 1347375694 value $value"	416	"tag 1347375694 value $value"
360	};	417	};
		418
		419	Example: provide your own filter function that looks up tags in your own
		420	hash:
		421
		422	my %my_filter = (
		423	998347484 => sub {
		424	my ($tag, $value);
		425
		426	"tag 998347484 value $value"
		427	};
		428	);
		429
		430	my $coder = CBOR::XS->new->filter (sub {
		431	&{ $my_filter{$_[0]} or return }
		432	});
		433
		434
		435	Example: use the safe filter function (see L<SECURITY CONSIDERATIONS> for
		436	more considerations on security).
		437
		438	CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
361		439
362	=item $cbor_data = $cbor->encode ($perl_scalar)	440	=item $cbor_data = $cbor->encode ($perl_scalar)
363		441
364	Converts the given Perl data structure (a scalar value) to its CBOR	442	Converts the given Perl data structure (a scalar value) to its CBOR
365	representation.	443	representation.
…		…
978	CBOR intact.	1056	CBOR intact.
979		1057
980		1058
981	=head1 SECURITY CONSIDERATIONS	1059	=head1 SECURITY CONSIDERATIONS
982		1060
983	When you are using CBOR in a protocol, talking to untrusted potentially	1061	Tl;dr... if you want to decode or encode CBOR from untrusted sources, you
984	hostile creatures requires relatively few measures.	1062	should start with a coder object created via C<new_safe>:
985		1063
		1064	my $coder = CBOR::XS->new_safe;
		1065
		1066	my $data = $coder->decode ($cbor_text);
		1067	my $cbor = $coder->encode ($data);
		1068
		1069	Longer version: When you are using CBOR in a protocol, talking to
		1070	untrusted potentially hostile creatures requires some thought:
		1071
		1072	=over 4
		1073
		1074	=item Security of the CBOR decoder itself
		1075
986	First of all, your CBOR decoder should be secure, that is, should not have	1076	First and foremost, your CBOR decoder should be secure, that is, should
		1077	not have any buffer overflows or similar bugs that could potentially be
987	any buffer overflows. Obviously, this module should ensure that and I am	1078	exploited. Obviously, this module should ensure that and I am trying hard
988	trying hard on making that true, but you never know.	1079	on making that true, but you never know.
989		1080
		1081	=item CBOR::XS can invoke almost arbitrary callbacks during decoding
		1082
990	Second, CBOR::XS supports object serialisation - decoding CBOR can cause	1083	CBOR::XS supports object serialisation - decoding CBOR can cause calls
991	calls to I<any> C<THAW> method in I<any> package that exists in your	1084	to I<any> C<THAW> method in I<any> package that exists in your process
992	process (that is, CBOR::XS will not try to load modules, but any existing	1085	(that is, CBOR::XS will not try to load modules, but any existing C<THAW>
993	C<THAW> method or function can be called, so they all have to be secure).	1086	method or function can be called, so they all have to be secure).
994		1087
		1088	Less obviously, it will also invoke C<TO_CBOR> and C<FREEZE> methods -
		1089	even if all your C<THAW> methods are secure, encoding data structures from
		1090	untrusted sources can invoke those and trigger bugs in those.
		1091
		1092	So, if you are not sure about the security of all the modules you
		1093	have loaded (you shouldn't), you should disable this part using
		1094	C<forbid_objects>.
		1095
		1096	=item CBOR can be extended with tags that call library code
		1097
		1098	CBOR can be extended with tags, and C<CBOR::XS> has a registry of
		1099	conversion functions for many existing tags that can be extended via
		1100	third-party modules (see the C<filter> method).
		1101
		1102	If you don't trust these, you should configure the "safe" filter function,
		1103	C<CBOR::XS::safe_filter>, which by default only includes conversion
		1104	functions that are considered "safe" by the author (but again, they can be
		1105	extended by third party modules).
		1106
		1107	Depending on your level of paranoia, you can use the "safe" filter:
		1108
		1109	$cbor->filter (\&CBOR::XS::safe_filter);
		1110
		1111	... your own filter...
		1112
		1113	$cbor->filter (sub { ... do your stuffs here ... });
		1114
		1115	... or even no filter at all, disabling all tag decoding:
		1116
		1117	$cbor->filter (sub { });
		1118
		1119	This is never a problem for encoding, as the tag mechanism only exists in
		1120	CBOR texts.
		1121
		1122	=item Resource-starving attacks: object memory usage
		1123
995	Third, you need to avoid resource-starving attacks. That means you should	1124	You need to avoid resource-starving attacks. That means you should limit
996	limit the size of CBOR data you accept, or make sure then when your	1125	the size of CBOR data you accept, or make sure then when your resources
997	resources run out, that's just fine (e.g. by using a separate process that	1126	run out, that's just fine (e.g. by using a separate process that can
998	can crash safely). The size of a CBOR string in octets is usually a good	1127	crash safely). The size of a CBOR string in octets is usually a good
999	indication of the size of the resources required to decode it into a Perl	1128	indication of the size of the resources required to decode it into a Perl
1000	structure. While CBOR::XS can check the size of the CBOR text, it might be	1129	structure. While CBOR::XS can check the size of the CBOR text (using
1001	too late when you already have it in memory, so you might want to check	1130	C<max_size>), it might be too late when you already have it in memory, so
1002	the size before you accept the string.	1131	you might want to check the size before you accept the string.
1003		1132
		1133	As for encoding, it is possible to construct data structures that are
		1134	relatively small but result in large CBOR texts (for example by having an
		1135	array full of references to the same big data structure, which will all be
		1136	deep-cloned during encoding by default). This is rarely an actual issue
		1137	(and the worst case is still just running out of memory), but you can
		1138	reduce this risk by using C<allow_sharing>.
		1139
		1140	=item Resource-starving attacks: stack overflows
		1141
1004	Fourth, CBOR::XS recurses using the C stack when decoding objects and	1142	CBOR::XS recurses using the C stack when decoding objects and arrays. The
1005	arrays. The C stack is a limited resource: for instance, on my amd64	1143	C stack is a limited resource: for instance, on my amd64 machine with 8MB
1006	machine with 8MB of stack size I can decode around 180k nested arrays but	1144	of stack size I can decode around 180k nested arrays but only 14k nested
1007	only 14k nested CBOR objects (due to perl itself recursing deeply on croak	1145	CBOR objects (due to perl itself recursing deeply on croak to free the
1008	to free the temporary). If that is exceeded, the program crashes. To be	1146	temporary). If that is exceeded, the program crashes. To be conservative,
1009	conservative, the default nesting limit is set to 512. If your process	1147	the default nesting limit is set to 512. If your process has a smaller
1010	has a smaller stack, you should adjust this setting accordingly with the	1148	stack, you should adjust this setting accordingly with the C<max_depth>
1011	C<max_depth> method.	1149	method.
		1150
		1151	=item Resource-starving attacks: CPU en-/decoding complexity
		1152
		1153	CBOR::XS will use the L<Math::BigInt>, L<Math::BigFloat> and
		1154	L<Math::BigRat> libraries to represent encode/decode bignums. These can
		1155	be very slow (as in, centuries of CPU time) and can even crash your
		1156	program (and are generally not very trustworthy). See the next section for
		1157	details.
		1158
		1159	=item Data breaches: leaking information in error messages
		1160
		1161	CBOR::XS might leak contents of your Perl data structures in its error
		1162	messages, so when you serialise sensitive information you might want to
		1163	make sure that exceptions thrown by CBOR::XS will not end up in front of
		1164	untrusted eyes.
		1165
		1166	=item Something else...
1012		1167
1013	Something else could bomb you, too, that I forgot to think of. In that	1168	Something else could bomb you, too, that I forgot to think of. In that
1014	case, you get to keep the pieces. I am always open for hints, though...	1169	case, you get to keep the pieces. I am always open for hints, though...
1015		1170
1016	Also keep in mind that CBOR::XS might leak contents of your Perl data	1171	=back
1017	structures in its error messages, so when you serialise sensitive
1018	information you might want to make sure that exceptions thrown by CBOR::XS
1019	will not end up in front of untrusted eyes.
1020		1172
1021		1173
1022	=head1 BIGNUM SECURITY CONSIDERATIONS	1174	=head1 BIGNUM SECURITY CONSIDERATIONS
1023		1175
1024	CBOR::XS provides a C<TO_CBOR> method for both L<Math::BigInt> and	1176	CBOR::XS provides a C<TO_CBOR> method for both L<Math::BigInt> and
…		…
1099	Please refrain from using rt.cpan.org or any other bug reporting	1251	Please refrain from using rt.cpan.org or any other bug reporting
1100	service. I put the contact address into my modules for a reason.	1252	service. I put the contact address into my modules for a reason.
1101		1253
1102	=cut	1254	=cut
1103		1255
1104	# clumsy hv_store-in-perl	1256	# clumsy and slow hv_store-in-hash helper function
1105	sub _hv_store {	1257	sub _hv_store {
1106	$_[0]{$_[1]} = $_[2];	1258	$_[0]{$_[1]} = $_[2];
1107	}	1259	}
1108		1260
1109	our %FILTER = (	1261	our %FILTER = (
…		…
1185	# 34 # base64 rfc46484, utf-8	1337	# 34 # base64 rfc46484, utf-8
1186	# 35 # regex pcre/ecma262, utf-8	1338	# 35 # regex pcre/ecma262, utf-8
1187	# 36 # mime message rfc2045, utf-8	1339	# 36 # mime message rfc2045, utf-8
1188	);	1340	);
1189		1341
1190	sub CBOR::XS::default_filter {	1342	sub default_filter {
1191	&{ $FILTER{$_[0]} or return }	1343	&{ $FILTER{$_[0]} or return }
		1344	}
		1345
		1346	our %SAFE_FILTER = map { $_ => $FILTER{$_} } 0, 1, 21, 22, 23, 32;
		1347
		1348	sub safe_filter {
		1349	&{ $SAFE_FILTER{$_[0]} or return }
1192	}	1350	}
1193		1351
1194	sub URI::TO_CBOR {	1352	sub URI::TO_CBOR {
1195	my $uri = $_[0]->as_string;	1353	my $uri = $_[0]->as_string;
1196	utf8::upgrade $uri;	1354	utf8::upgrade $uri;

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Comparing CBOR-XS/XS.pm (file contents): Revision 1.64 by root, Fri Nov 25 23:37:27 2016 UTC vs. Revision 1.65 by root, Sat Nov 26 00:47:02 2016 UTC

Diff Legend

Comparing CBOR-XS/XS.pm (file contents):
Revision 1.64 by root, Fri Nov 25 23:37:27 2016 UTC vs.
Revision 1.65 by root, Sat Nov 26 00:47:02 2016 UTC