1 /* $OpenBSD: bs_ber.c,v 1.2 2021/12/15 18:02:39 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
18 #include <string.h>
19
20 #include "bytestring.h"
21
22 /*
23 * kMaxDepth is a just a sanity limit. The code should be such that the length
24 * of the input being processes always decreases. None the less, a very large
25 * input could otherwise cause the stack to overflow.
26 */
27 static const unsigned int kMaxDepth = 2048;
28
29 /* Non-strict version that allows a relaxed DER with indefinite form. */
30 static int
cbs_nonstrict_get_any_asn1_element(CBS * cbs,CBS * out,unsigned int * out_tag,size_t * out_header_len)31 cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
32 size_t *out_header_len)
33 {
34 return cbs_get_any_asn1_element_internal(cbs, out,
35 out_tag, out_header_len, 0);
36 }
37
38 /*
39 * cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
40 * |*indefinite_found| depending on whether an indefinite length element was
41 * found. The value of |orig_in| is not modified.
42 *
43 * Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
44 */
45 static int
cbs_find_indefinite(const CBS * orig_in,char * indefinite_found,unsigned int depth)46 cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
47 unsigned int depth)
48 {
49 CBS in;
50
51 if (depth > kMaxDepth)
52 return 0;
53
54 CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
55
56 while (CBS_len(&in) > 0) {
57 CBS contents;
58 unsigned int tag;
59 size_t header_len;
60
61 if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
62 &header_len))
63 return 0;
64
65 /* Indefinite form not allowed by DER. */
66 if (CBS_len(&contents) == header_len && header_len > 0 &&
67 CBS_data(&contents)[header_len - 1] == 0x80) {
68 *indefinite_found = 1;
69 return 1;
70 }
71 if (tag & CBS_ASN1_CONSTRUCTED) {
72 if (!CBS_skip(&contents, header_len) ||
73 !cbs_find_indefinite(&contents, indefinite_found,
74 depth + 1))
75 return 0;
76 }
77 }
78
79 *indefinite_found = 0;
80 return 1;
81 }
82
83 /*
84 * is_primitive_type returns true if |tag| likely a primitive type. Normally
85 * one can just test the "constructed" bit in the tag but, in BER, even
86 * primitive tags can have the constructed bit if they have indefinite
87 * length.
88 */
89 static char
is_primitive_type(unsigned int tag)90 is_primitive_type(unsigned int tag)
91 {
92 return (tag & 0xc0) == 0 &&
93 (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
94 (tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
95 }
96
97 /*
98 * is_eoc returns true if |header_len| and |contents|, as returned by
99 * |cbs_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
100 * value.
101 */
102 static char
is_eoc(size_t header_len,CBS * contents)103 is_eoc(size_t header_len, CBS *contents)
104 {
105 const unsigned char eoc[] = {0x0, 0x0};
106
107 return header_len == 2 && CBS_mem_equal(contents, eoc, 2);
108 }
109
110 /*
111 * cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
112 * indefinite form) from |in| and writes definite form DER data to |out|. If
113 * |squash_header| is set then the top-level of elements from |in| will not
114 * have their headers written. This is used when concatenating the fragments of
115 * an indefinite length, primitive value. If |looking_for_eoc| is set then any
116 * EOC elements found will cause the function to return after consuming it.
117 * It returns one on success and zero on error.
118 */
119 static int
cbs_convert_indefinite(CBS * in,CBB * out,char squash_header,char looking_for_eoc,unsigned int depth)120 cbs_convert_indefinite(CBS *in, CBB *out, char squash_header,
121 char looking_for_eoc, unsigned int depth)
122 {
123 if (depth > kMaxDepth)
124 return 0;
125
126 while (CBS_len(in) > 0) {
127 CBS contents;
128 unsigned int tag;
129 size_t header_len;
130 CBB *out_contents, out_contents_storage;
131
132 if (!cbs_nonstrict_get_any_asn1_element(in, &contents, &tag,
133 &header_len))
134 return 0;
135
136 out_contents = out;
137
138 if (CBS_len(&contents) == header_len) {
139 if (is_eoc(header_len, &contents))
140 return looking_for_eoc;
141
142 if (header_len > 0 &&
143 CBS_data(&contents)[header_len - 1] == 0x80) {
144 /*
145 * This is an indefinite length element. If
146 * it's a SEQUENCE or SET then we just need to
147 * write the out the contents as normal, but
148 * with a concrete length prefix.
149 *
150 * If it's a something else then the contents
151 * will be a series of DER elements of the same
152 * type which need to be concatenated.
153 */
154 const char context_specific = (tag & 0xc0)
155 == 0x80;
156 char squash_child_headers =
157 is_primitive_type(tag);
158
159 /*
160 * This is a hack, but it sufficies to handle
161 * NSS's output. If we find an indefinite
162 * length, context-specific tag with a definite,
163 * primtive tag inside it, then we assume that
164 * the context-specific tag is implicit and the
165 * tags within are fragments of a primitive type
166 * that need to be concatenated.
167 */
168 if (context_specific &&
169 (tag & CBS_ASN1_CONSTRUCTED)) {
170 CBS in_copy, inner_contents;
171 unsigned int inner_tag;
172 size_t inner_header_len;
173
174 CBS_init(&in_copy, CBS_data(in),
175 CBS_len(in));
176 if (!cbs_nonstrict_get_any_asn1_element(
177 &in_copy, &inner_contents,
178 &inner_tag, &inner_header_len))
179 return 0;
180
181 if (CBS_len(&inner_contents) >
182 inner_header_len &&
183 is_primitive_type(inner_tag))
184 squash_child_headers = 1;
185 }
186
187 if (!squash_header) {
188 unsigned int out_tag = tag;
189
190 if (squash_child_headers)
191 out_tag &=
192 ~CBS_ASN1_CONSTRUCTED;
193
194 if (!CBB_add_asn1(out,
195 &out_contents_storage, out_tag))
196 return 0;
197
198 out_contents = &out_contents_storage;
199 }
200
201 if (!cbs_convert_indefinite(in, out_contents,
202 squash_child_headers,
203 1 /* looking for eoc */, depth + 1))
204 return 0;
205
206 if (out_contents != out && !CBB_flush(out))
207 return 0;
208
209 continue;
210 }
211 }
212
213 if (!squash_header) {
214 if (!CBB_add_asn1(out, &out_contents_storage, tag))
215 return 0;
216
217 out_contents = &out_contents_storage;
218 }
219
220 if (!CBS_skip(&contents, header_len))
221 return 0;
222
223 if (tag & CBS_ASN1_CONSTRUCTED) {
224 if (!cbs_convert_indefinite(&contents, out_contents,
225 0 /* don't squash header */,
226 0 /* not looking for eoc */, depth + 1))
227 return 0;
228 } else {
229 if (!CBB_add_bytes(out_contents, CBS_data(&contents),
230 CBS_len(&contents)))
231 return 0;
232 }
233
234 if (out_contents != out && !CBB_flush(out))
235 return 0;
236 }
237
238 return looking_for_eoc == 0;
239 }
240
241 int
CBS_asn1_indefinite_to_definite(CBS * in,uint8_t ** out,size_t * out_len)242 CBS_asn1_indefinite_to_definite(CBS *in, uint8_t **out, size_t *out_len)
243 {
244 CBB cbb;
245
246 /*
247 * First, do a quick walk to find any indefinite-length elements. Most
248 * of the time we hope that there aren't any and thus we can quickly
249 * return.
250 */
251 char conversion_needed;
252 if (!cbs_find_indefinite(in, &conversion_needed, 0))
253 return 0;
254
255 if (!conversion_needed) {
256 *out = NULL;
257 *out_len = 0;
258 return 1;
259 }
260
261 if (!CBB_init(&cbb, CBS_len(in)))
262 return 0;
263 if (!cbs_convert_indefinite(in, &cbb, 0, 0, 0)) {
264 CBB_cleanup(&cbb);
265 return 0;
266 }
267
268 return CBB_finish(&cbb, out, out_len);
269 }
270