1/* Copyright (c) 2014, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15#include <openssl/bytestring.h>
16
17#include <string.h>
18
19#include "internal.h"
20
21
22/* kMaxDepth is a just a sanity limit. The code should be such that the length
23 * of the input being processes always decreases. None the less, a very large
24 * input could otherwise cause the stack to overflow. */
25static const unsigned kMaxDepth = 2048;
26
27/* cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found|
28 * depending on whether an indefinite length element was found. The value of
29 * |in| is not changed. It returns one on success (i.e. |*ber_found| was set)
30 * and zero on error. */
31static int cbs_find_ber(CBS *orig_in, char *ber_found, unsigned depth) {
32  CBS in;
33
34  if (depth > kMaxDepth) {
35    return 0;
36  }
37
38  CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
39  *ber_found = 0;
40
41  while (CBS_len(&in) > 0) {
42    CBS contents;
43    unsigned tag;
44    size_t header_len;
45
46    if (!CBS_get_any_ber_asn1_element(&in, &contents, &tag, &header_len)) {
47      return 0;
48    }
49    if (CBS_len(&contents) == header_len &&
50        header_len > 0 &&
51        CBS_data(&contents)[header_len-1] == 0x80) {
52      *ber_found = 1;
53      return 1;
54    }
55    if (tag & CBS_ASN1_CONSTRUCTED) {
56      if (!CBS_skip(&contents, header_len) ||
57          !cbs_find_ber(&contents, ber_found, depth + 1)) {
58        return 0;
59      }
60    }
61  }
62
63  return 1;
64}
65
66/* is_primitive_type returns true if |tag| likely a primitive type. Normally
67 * one can just test the "constructed" bit in the tag but, in BER, even
68 * primitive tags can have the constructed bit if they have indefinite
69 * length. */
70static char is_primitive_type(unsigned tag) {
71  return (tag & 0xc0) == 0 &&
72         (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
73         (tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
74}
75
76/* is_eoc returns true if |header_len| and |contents|, as returned by
77 * |CBS_get_any_ber_asn1_element|, indicate an "end of contents" (EOC) value. */
78static char is_eoc(size_t header_len, CBS *contents) {
79  return header_len == 2 && CBS_len(contents) == 2 &&
80         memcmp(CBS_data(contents), "\x00\x00", 2) == 0;
81}
82
83/* cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If
84 * |squash_header| is set then the top-level of elements from |in| will not
85 * have their headers written. This is used when concatenating the fragments of
86 * an indefinite length, primitive value. If |looking_for_eoc| is set then any
87 * EOC elements found will cause the function to return after consuming it.
88 * It returns one on success and zero on error. */
89static int cbs_convert_ber(CBS *in, CBB *out, char squash_header,
90                           char looking_for_eoc, unsigned depth) {
91  if (depth > kMaxDepth) {
92    return 0;
93  }
94
95  while (CBS_len(in) > 0) {
96    CBS contents;
97    unsigned tag;
98    size_t header_len;
99    CBB *out_contents, out_contents_storage;
100
101    if (!CBS_get_any_ber_asn1_element(in, &contents, &tag, &header_len)) {
102      return 0;
103    }
104    out_contents = out;
105
106    if (CBS_len(&contents) == header_len) {
107      if (is_eoc(header_len, &contents)) {
108        return looking_for_eoc;
109      }
110
111      if (header_len > 0 && CBS_data(&contents)[header_len - 1] == 0x80) {
112        /* This is an indefinite length element. If it's a SEQUENCE or SET then
113         * we just need to write the out the contents as normal, but with a
114         * concrete length prefix.
115         *
116         * If it's a something else then the contents will be a series of BER
117         * elements of the same type which need to be concatenated. */
118        const char context_specific = (tag & 0xc0) == 0x80;
119        char squash_child_headers = is_primitive_type(tag);
120
121        /* This is a hack, but it sufficies to handle NSS's output. If we find
122         * an indefinite length, context-specific tag with a definite, primtive
123         * tag inside it, then we assume that the context-specific tag is
124         * implicit and the tags within are fragments of a primitive type that
125         * need to be concatenated. */
126        if (context_specific && (tag & CBS_ASN1_CONSTRUCTED)) {
127          CBS in_copy, inner_contents;
128          unsigned inner_tag;
129          size_t inner_header_len;
130
131          CBS_init(&in_copy, CBS_data(in), CBS_len(in));
132          if (!CBS_get_any_ber_asn1_element(&in_copy, &inner_contents,
133                                            &inner_tag, &inner_header_len)) {
134            return 0;
135          }
136          if (CBS_len(&inner_contents) > inner_header_len &&
137              is_primitive_type(inner_tag)) {
138            squash_child_headers = 1;
139          }
140        }
141
142        if (!squash_header) {
143          unsigned out_tag = tag;
144          if (squash_child_headers) {
145            out_tag &= ~CBS_ASN1_CONSTRUCTED;
146          }
147          if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) {
148            return 0;
149          }
150          out_contents = &out_contents_storage;
151        }
152
153        if (!cbs_convert_ber(in, out_contents,
154                             squash_child_headers,
155                             1 /* looking for eoc */, depth + 1)) {
156          return 0;
157        }
158        if (out_contents != out && !CBB_flush(out)) {
159          return 0;
160        }
161        continue;
162      }
163    }
164
165    if (!squash_header) {
166      if (!CBB_add_asn1(out, &out_contents_storage, tag)) {
167        return 0;
168      }
169      out_contents = &out_contents_storage;
170    }
171
172    if (!CBS_skip(&contents, header_len)) {
173      return 0;
174    }
175
176    if (tag & CBS_ASN1_CONSTRUCTED) {
177      if (!cbs_convert_ber(&contents, out_contents, 0 /* don't squash header */,
178                           0 /* not looking for eoc */, depth + 1)) {
179        return 0;
180      }
181    } else {
182      if (!CBB_add_bytes(out_contents, CBS_data(&contents),
183                         CBS_len(&contents))) {
184        return 0;
185      }
186    }
187
188    if (out_contents != out && !CBB_flush(out)) {
189      return 0;
190    }
191  }
192
193  return looking_for_eoc == 0;
194}
195
196int CBS_asn1_ber_to_der(CBS *in, uint8_t **out, size_t *out_len) {
197  CBB cbb;
198
199  /* First, do a quick walk to find any indefinite-length elements. Most of the
200   * time we hope that there aren't any and thus we can quickly return. */
201  char conversion_needed;
202  if (!cbs_find_ber(in, &conversion_needed, 0)) {
203    return 0;
204  }
205
206  if (!conversion_needed) {
207    *out = NULL;
208    *out_len = 0;
209    return 1;
210  }
211
212  if (!CBB_init(&cbb, CBS_len(in))) {
213    return 0;
214  }
215  if (!cbs_convert_ber(in, &cbb, 0, 0, 0)) {
216    CBB_cleanup(&cbb);
217    return 0;
218  }
219
220  return CBB_finish(&cbb, out, out_len);
221}
222