1 /* $OpenBSD: bs_ber.c,v 1.9 2016/12/03 12:34:35 jsing Exp $ */
2 /*
3 * Copyright (c) 2014, Google Inc.
4 *
5 * Permission to use, copy, modify, and/or distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
12 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
14 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
15 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
16
17 #include <string.h>
18
19 #include <openssl/opensslconf.h>
20
21 #include "bytestring.h"
22
23 /*
24 * kMaxDepth is a just a sanity limit. The code should be such that the length
25 * of the input being processes always decreases. None the less, a very large
26 * input could otherwise cause the stack to overflow.
27 */
28 static const unsigned int kMaxDepth = 2048;
29
30 /* Non-strict version that allows a relaxed DER with indefinite form. */
31 static int
cbs_nonstrict_get_any_asn1_element(CBS * cbs,CBS * out,unsigned int * out_tag,size_t * out_header_len)32 cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
33 size_t *out_header_len)
34 {
35 return cbs_get_any_asn1_element_internal(cbs, out,
36 out_tag, out_header_len, 0);
37 }
38
39 /*
40 * cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
41 * |*indefinite_found| depending on whether an indefinite length element was
42 * found. The value of |orig_in| is not modified.
43 *
44 * Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
45 */
46 static int
cbs_find_indefinite(const CBS * orig_in,char * indefinite_found,unsigned int depth)47 cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
48 unsigned int depth)
49 {
50 CBS in;
51
52 if (depth > kMaxDepth)
53 return 0;
54
55 CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
56
57 while (CBS_len(&in) > 0) {
58 CBS contents;
59 unsigned int tag;
60 size_t header_len;
61
62 if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
63 &header_len))
64 return 0;
65
66 /* Indefinite form not allowed by DER. */
67 if (CBS_len(&contents) == header_len && header_len > 0 &&
68 CBS_data(&contents)[header_len - 1] == 0x80) {
69 *indefinite_found = 1;
70 return 1;
71 }
72 if (tag & CBS_ASN1_CONSTRUCTED) {
73 if (!CBS_skip(&contents, header_len) ||
74 !cbs_find_indefinite(&contents, indefinite_found,
75 depth + 1))
76 return 0;
77 }
78 }
79
80 *indefinite_found = 0;
81 return 1;
82 }
83
84 /*
85 * is_primitive_type returns true if |tag| likely a primitive type. Normally
86 * one can just test the "constructed" bit in the tag but, in BER, even
87 * primitive tags can have the constructed bit if they have indefinite
88 * length.
89 */
90 static char
is_primitive_type(unsigned int tag)91 is_primitive_type(unsigned int tag)
92 {
93 return (tag & 0xc0) == 0 &&
94 (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
95 (tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
96 }
97
98 /*
99 * is_eoc returns true if |header_len| and |contents|, as returned by
100 * |cbs_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
101 * value.
102 */
103 static char
is_eoc(size_t header_len,CBS * contents)104 is_eoc(size_t header_len, CBS *contents)
105 {
106 const unsigned char eoc[] = {0x0, 0x0};
107
108 return header_len == 2 && CBS_mem_equal(contents, eoc, 2);
109 }
110
111 /*
112 * cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
113 * indefinite form) from |in| and writes definite form DER data to |out|. If
114 * |squash_header| is set then the top-level of elements from |in| will not
115 * have their headers written. This is used when concatenating the fragments of
116 * an indefinite length, primitive value. If |looking_for_eoc| is set then any
117 * EOC elements found will cause the function to return after consuming it.
118 * It returns one on success and zero on error.
119 */
120 static int
cbs_convert_indefinite(CBS * in,CBB * out,char squash_header,char looking_for_eoc,unsigned int depth)121 cbs_convert_indefinite(CBS *in, CBB *out, char squash_header,
122 char looking_for_eoc, unsigned int depth)
123 {
124 if (depth > kMaxDepth)
125 return 0;
126
127 while (CBS_len(in) > 0) {
128 CBS contents;
129 unsigned int tag;
130 size_t header_len;
131 CBB *out_contents, out_contents_storage;
132
133 if (!cbs_nonstrict_get_any_asn1_element(in, &contents, &tag,
134 &header_len))
135 return 0;
136
137 out_contents = out;
138
139 if (CBS_len(&contents) == header_len) {
140 if (is_eoc(header_len, &contents))
141 return looking_for_eoc;
142
143 if (header_len > 0 &&
144 CBS_data(&contents)[header_len - 1] == 0x80) {
145 /*
146 * This is an indefinite length element. If
147 * it's a SEQUENCE or SET then we just need to
148 * write the out the contents as normal, but
149 * with a concrete length prefix.
150 *
151 * If it's a something else then the contents
152 * will be a series of DER elements of the same
153 * type which need to be concatenated.
154 */
155 const char context_specific = (tag & 0xc0)
156 == 0x80;
157 char squash_child_headers =
158 is_primitive_type(tag);
159
160 /*
161 * This is a hack, but it sufficies to handle
162 * NSS's output. If we find an indefinite
163 * length, context-specific tag with a definite,
164 * primtive tag inside it, then we assume that
165 * the context-specific tag is implicit and the
166 * tags within are fragments of a primitive type
167 * that need to be concatenated.
168 */
169 if (context_specific &&
170 (tag & CBS_ASN1_CONSTRUCTED)) {
171 CBS in_copy, inner_contents;
172 unsigned int inner_tag;
173 size_t inner_header_len;
174
175 CBS_init(&in_copy, CBS_data(in),
176 CBS_len(in));
177 if (!cbs_nonstrict_get_any_asn1_element(
178 &in_copy, &inner_contents,
179 &inner_tag, &inner_header_len))
180 return 0;
181
182 if (CBS_len(&inner_contents) >
183 inner_header_len &&
184 is_primitive_type(inner_tag))
185 squash_child_headers = 1;
186 }
187
188 if (!squash_header) {
189 unsigned int out_tag = tag;
190
191 if (squash_child_headers)
192 out_tag &=
193 ~CBS_ASN1_CONSTRUCTED;
194
195 if (!CBB_add_asn1(out,
196 &out_contents_storage, out_tag))
197 return 0;
198
199 out_contents = &out_contents_storage;
200 }
201
202 if (!cbs_convert_indefinite(in, out_contents,
203 squash_child_headers,
204 1 /* looking for eoc */, depth + 1))
205 return 0;
206
207 if (out_contents != out && !CBB_flush(out))
208 return 0;
209
210 continue;
211 }
212 }
213
214 if (!squash_header) {
215 if (!CBB_add_asn1(out, &out_contents_storage, tag))
216 return 0;
217
218 out_contents = &out_contents_storage;
219 }
220
221 if (!CBS_skip(&contents, header_len))
222 return 0;
223
224 if (tag & CBS_ASN1_CONSTRUCTED) {
225 if (!cbs_convert_indefinite(&contents, out_contents,
226 0 /* don't squash header */,
227 0 /* not looking for eoc */, depth + 1))
228 return 0;
229 } else {
230 if (!CBB_add_bytes(out_contents, CBS_data(&contents),
231 CBS_len(&contents)))
232 return 0;
233 }
234
235 if (out_contents != out && !CBB_flush(out))
236 return 0;
237 }
238
239 return looking_for_eoc == 0;
240 }
241
242 int
CBS_asn1_indefinite_to_definite(CBS * in,uint8_t ** out,size_t * out_len)243 CBS_asn1_indefinite_to_definite(CBS *in, uint8_t **out, size_t *out_len)
244 {
245 CBB cbb;
246
247 /*
248 * First, do a quick walk to find any indefinite-length elements. Most
249 * of the time we hope that there aren't any and thus we can quickly
250 * return.
251 */
252 char conversion_needed;
253 if (!cbs_find_indefinite(in, &conversion_needed, 0))
254 return 0;
255
256 if (!conversion_needed) {
257 *out = NULL;
258 *out_len = 0;
259 return 1;
260 }
261
262 if (!CBB_init(&cbb, CBS_len(in)))
263 return 0;
264 if (!cbs_convert_indefinite(in, &cbb, 0, 0, 0)) {
265 CBB_cleanup(&cbb);
266 return 0;
267 }
268
269 return CBB_finish(&cbb, out, out_len);
270 }
271