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 <assert.h>
18 #include <string.h>
19 
20 #include "internal.h"
21 #include "../internal.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 static const unsigned kMaxDepth = 2048;
28 
29 /* is_string_type returns one if |tag| is a string type and zero otherwise. It
30  * ignores the constructed bit. */
is_string_type(unsigned tag)31 static int is_string_type(unsigned tag) {
32   if ((tag & 0xc0) != 0) {
33     return 0;
34   }
35   switch (tag & 0x1f) {
36     case CBS_ASN1_BITSTRING:
37     case CBS_ASN1_OCTETSTRING:
38     case CBS_ASN1_UTF8STRING:
39     case CBS_ASN1_NUMERICSTRING:
40     case CBS_ASN1_PRINTABLESTRING:
41     case CBS_ASN1_T61STRING:
42     case CBS_ASN1_VIDEOTEXSTRING:
43     case CBS_ASN1_IA5STRING:
44     case CBS_ASN1_GRAPHICSTRING:
45     case CBS_ASN1_VISIBLESTRING:
46     case CBS_ASN1_GENERALSTRING:
47     case CBS_ASN1_UNIVERSALSTRING:
48     case CBS_ASN1_BMPSTRING:
49       return 1;
50     default:
51       return 0;
52   }
53 }
54 
55 /* cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found|
56  * depending on whether an indefinite length element or constructed string was
57  * found. The value of |orig_in| is not changed. It returns one on success (i.e.
58  * |*ber_found| was set) and zero on error. */
cbs_find_ber(const CBS * orig_in,char * ber_found,unsigned depth)59 static int cbs_find_ber(const CBS *orig_in, char *ber_found, unsigned depth) {
60   CBS in;
61 
62   if (depth > kMaxDepth) {
63     return 0;
64   }
65 
66   CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
67   *ber_found = 0;
68 
69   while (CBS_len(&in) > 0) {
70     CBS contents;
71     unsigned tag;
72     size_t header_len;
73 
74     if (!CBS_get_any_ber_asn1_element(&in, &contents, &tag, &header_len)) {
75       return 0;
76     }
77     if (CBS_len(&contents) == header_len &&
78         header_len > 0 &&
79         CBS_data(&contents)[header_len-1] == 0x80) {
80       /* Found an indefinite-length element. */
81       *ber_found = 1;
82       return 1;
83     }
84     if (tag & CBS_ASN1_CONSTRUCTED) {
85       if (is_string_type(tag)) {
86         /* Constructed strings are only legal in BER and require conversion. */
87         *ber_found = 1;
88         return 1;
89       }
90       if (!CBS_skip(&contents, header_len) ||
91           !cbs_find_ber(&contents, ber_found, depth + 1)) {
92         return 0;
93       }
94     }
95   }
96 
97   return 1;
98 }
99 
100 /* is_eoc returns true if |header_len| and |contents|, as returned by
101  * |CBS_get_any_ber_asn1_element|, indicate an "end of contents" (EOC) value. */
is_eoc(size_t header_len,CBS * contents)102 static char is_eoc(size_t header_len, CBS *contents) {
103   return header_len == 2 && CBS_len(contents) == 2 &&
104          OPENSSL_memcmp(CBS_data(contents), "\x00\x00", 2) == 0;
105 }
106 
107 /* cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If
108  * |string_tag| is non-zero, then all elements must match |string_tag| up to the
109  * constructed bit and primitive element bodies are written to |out| without
110  * element headers. This is used when concatenating the fragments of a
111  * constructed string. If |looking_for_eoc| is set then any EOC elements found
112  * will cause the function to return after consuming it. It returns one on
113  * success and zero on error. */
cbs_convert_ber(CBS * in,CBB * out,unsigned string_tag,char looking_for_eoc,unsigned depth)114 static int cbs_convert_ber(CBS *in, CBB *out, unsigned string_tag,
115                            char looking_for_eoc, unsigned depth) {
116   assert(!(string_tag & CBS_ASN1_CONSTRUCTED));
117 
118   if (depth > kMaxDepth) {
119     return 0;
120   }
121 
122   while (CBS_len(in) > 0) {
123     CBS contents;
124     unsigned tag, child_string_tag = string_tag;
125     size_t header_len;
126     CBB *out_contents, out_contents_storage;
127 
128     if (!CBS_get_any_ber_asn1_element(in, &contents, &tag, &header_len)) {
129       return 0;
130     }
131 
132     if (is_eoc(header_len, &contents)) {
133       return looking_for_eoc;
134     }
135 
136     if (string_tag != 0) {
137       /* This is part of a constructed string. All elements must match
138        * |string_tag| up to the constructed bit and get appended to |out|
139        * without a child element. */
140       if ((tag & ~CBS_ASN1_CONSTRUCTED) != string_tag) {
141         return 0;
142       }
143       out_contents = out;
144     } else {
145       unsigned out_tag = tag;
146       if ((tag & CBS_ASN1_CONSTRUCTED) && is_string_type(tag)) {
147         /* If a constructed string, clear the constructed bit and inform
148          * children to concatenate bodies. */
149         out_tag &= ~CBS_ASN1_CONSTRUCTED;
150         child_string_tag = out_tag;
151       }
152       if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) {
153         return 0;
154       }
155       out_contents = &out_contents_storage;
156     }
157 
158     if (CBS_len(&contents) == header_len && header_len > 0 &&
159         CBS_data(&contents)[header_len - 1] == 0x80) {
160       /* This is an indefinite length element. */
161       if (!cbs_convert_ber(in, out_contents, child_string_tag,
162                            1 /* looking for eoc */, depth + 1) ||
163           !CBB_flush(out)) {
164         return 0;
165       }
166       continue;
167     }
168 
169     if (!CBS_skip(&contents, header_len)) {
170       return 0;
171     }
172 
173     if (tag & CBS_ASN1_CONSTRUCTED) {
174       /* Recurse into children. */
175       if (!cbs_convert_ber(&contents, out_contents, child_string_tag,
176                            0 /* not looking for eoc */, depth + 1)) {
177         return 0;
178       }
179     } else {
180       /* Copy primitive contents as-is. */
181       if (!CBB_add_bytes(out_contents, CBS_data(&contents),
182                          CBS_len(&contents))) {
183         return 0;
184       }
185     }
186 
187     if (!CBB_flush(out)) {
188       return 0;
189     }
190   }
191 
192   return looking_for_eoc == 0;
193 }
194 
CBS_asn1_ber_to_der(CBS * in,uint8_t ** out,size_t * out_len)195 int CBS_asn1_ber_to_der(CBS *in, uint8_t **out, size_t *out_len) {
196   CBB cbb;
197 
198   /* First, do a quick walk to find any indefinite-length elements. Most of the
199    * time we hope that there aren't any and thus we can quickly return. */
200   char conversion_needed;
201   if (!cbs_find_ber(in, &conversion_needed, 0)) {
202     return 0;
203   }
204 
205   if (!conversion_needed) {
206     *out = NULL;
207     *out_len = 0;
208     return 1;
209   }
210 
211   if (!CBB_init(&cbb, CBS_len(in)) ||
212       !cbs_convert_ber(in, &cbb, 0, 0, 0) ||
213       !CBB_finish(&cbb, out, out_len)) {
214     CBB_cleanup(&cbb);
215     return 0;
216   }
217 
218   return 1;
219 }
220 
CBS_get_asn1_implicit_string(CBS * in,CBS * out,uint8_t ** out_storage,unsigned outer_tag,unsigned inner_tag)221 int CBS_get_asn1_implicit_string(CBS *in, CBS *out, uint8_t **out_storage,
222                                  unsigned outer_tag, unsigned inner_tag) {
223   assert(!(outer_tag & CBS_ASN1_CONSTRUCTED));
224   assert(!(inner_tag & CBS_ASN1_CONSTRUCTED));
225   assert(is_string_type(inner_tag));
226 
227   if (CBS_peek_asn1_tag(in, outer_tag)) {
228     /* Normal implicitly-tagged string. */
229     *out_storage = NULL;
230     return CBS_get_asn1(in, out, outer_tag);
231   }
232 
233   /* Otherwise, try to parse an implicitly-tagged constructed string.
234    * |CBS_asn1_ber_to_der| is assumed to have run, so only allow one level deep
235    * of nesting. */
236   CBB result;
237   CBS child;
238   if (!CBB_init(&result, CBS_len(in)) ||
239       !CBS_get_asn1(in, &child, outer_tag | CBS_ASN1_CONSTRUCTED)) {
240     goto err;
241   }
242 
243   while (CBS_len(&child) > 0) {
244     CBS chunk;
245     if (!CBS_get_asn1(&child, &chunk, inner_tag) ||
246         !CBB_add_bytes(&result, CBS_data(&chunk), CBS_len(&chunk))) {
247       goto err;
248     }
249   }
250 
251   uint8_t *data;
252   size_t len;
253   if (!CBB_finish(&result, &data, &len)) {
254     goto err;
255   }
256 
257   CBS_init(out, data, len);
258   *out_storage = data;
259   return 1;
260 
261 err:
262   CBB_cleanup(&result);
263   return 0;
264 }
265