1 /*
2 * ASN.1 buffer writing functionality
3 *
4 * Copyright The Mbed TLS Contributors
5 * SPDX-License-Identifier: Apache-2.0
6 *
7 * Licensed under the Apache License, Version 2.0 (the "License"); you may
8 * not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19
20 #include "common.h"
21
22 #if defined(MBEDTLS_ASN1_WRITE_C)
23
24 #include "mbedtls/asn1write.h"
25 #include "mbedtls/error.h"
26
27 #include <string.h>
28
29 #include "mbedtls/platform.h"
30
mbedtls_asn1_write_len(unsigned char ** p,const unsigned char * start,size_t len)31 int mbedtls_asn1_write_len(unsigned char **p, const unsigned char *start, size_t len)
32 {
33 if (len < 0x80) {
34 if (*p - start < 1) {
35 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
36 }
37
38 *--(*p) = (unsigned char) len;
39 return 1;
40 }
41
42 if (len <= 0xFF) {
43 if (*p - start < 2) {
44 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
45 }
46
47 *--(*p) = (unsigned char) len;
48 *--(*p) = 0x81;
49 return 2;
50 }
51
52 if (len <= 0xFFFF) {
53 if (*p - start < 3) {
54 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
55 }
56
57 *--(*p) = MBEDTLS_BYTE_0(len);
58 *--(*p) = MBEDTLS_BYTE_1(len);
59 *--(*p) = 0x82;
60 return 3;
61 }
62
63 if (len <= 0xFFFFFF) {
64 if (*p - start < 4) {
65 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
66 }
67
68 *--(*p) = MBEDTLS_BYTE_0(len);
69 *--(*p) = MBEDTLS_BYTE_1(len);
70 *--(*p) = MBEDTLS_BYTE_2(len);
71 *--(*p) = 0x83;
72 return 4;
73 }
74
75 int len_is_valid = 1;
76 #if SIZE_MAX > 0xFFFFFFFF
77 len_is_valid = (len <= 0xFFFFFFFF);
78 #endif
79 if (len_is_valid) {
80 if (*p - start < 5) {
81 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
82 }
83
84 *--(*p) = MBEDTLS_BYTE_0(len);
85 *--(*p) = MBEDTLS_BYTE_1(len);
86 *--(*p) = MBEDTLS_BYTE_2(len);
87 *--(*p) = MBEDTLS_BYTE_3(len);
88 *--(*p) = 0x84;
89 return 5;
90 }
91
92 return MBEDTLS_ERR_ASN1_INVALID_LENGTH;
93 }
94
mbedtls_asn1_write_tag(unsigned char ** p,const unsigned char * start,unsigned char tag)95 int mbedtls_asn1_write_tag(unsigned char **p, const unsigned char *start, unsigned char tag)
96 {
97 if (*p - start < 1) {
98 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
99 }
100
101 *--(*p) = tag;
102
103 return 1;
104 }
105
mbedtls_asn1_write_raw_buffer(unsigned char ** p,const unsigned char * start,const unsigned char * buf,size_t size)106 int mbedtls_asn1_write_raw_buffer(unsigned char **p, const unsigned char *start,
107 const unsigned char *buf, size_t size)
108 {
109 size_t len = 0;
110
111 if (*p < start || (size_t) (*p - start) < size) {
112 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
113 }
114
115 len = size;
116 (*p) -= len;
117 memcpy(*p, buf, len);
118
119 return (int) len;
120 }
121
122 #if defined(MBEDTLS_BIGNUM_C)
mbedtls_asn1_write_mpi(unsigned char ** p,const unsigned char * start,const mbedtls_mpi * X)123 int mbedtls_asn1_write_mpi(unsigned char **p, const unsigned char *start, const mbedtls_mpi *X)
124 {
125 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
126 size_t len = 0;
127
128 // Write the MPI
129 //
130 len = mbedtls_mpi_size(X);
131
132 /* DER represents 0 with a sign bit (0=nonnegative) and 7 value bits, not
133 * as 0 digits. We need to end up with 020100, not with 0200. */
134 if (len == 0) {
135 len = 1;
136 }
137
138 if (*p < start || (size_t) (*p - start) < len) {
139 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
140 }
141
142 (*p) -= len;
143 MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(X, *p, len));
144
145 // DER format assumes 2s complement for numbers, so the leftmost bit
146 // should be 0 for positive numbers and 1 for negative numbers.
147 //
148 if (X->s == 1 && **p & 0x80) {
149 if (*p - start < 1) {
150 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
151 }
152
153 *--(*p) = 0x00;
154 len += 1;
155 }
156
157 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
158 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_INTEGER));
159
160 ret = (int) len;
161
162 cleanup:
163 return ret;
164 }
165 #endif /* MBEDTLS_BIGNUM_C */
166
mbedtls_asn1_write_null(unsigned char ** p,const unsigned char * start)167 int mbedtls_asn1_write_null(unsigned char **p, const unsigned char *start)
168 {
169 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
170 size_t len = 0;
171
172 // Write NULL
173 //
174 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, 0));
175 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_NULL));
176
177 return (int) len;
178 }
179
mbedtls_asn1_write_oid(unsigned char ** p,const unsigned char * start,const char * oid,size_t oid_len)180 int mbedtls_asn1_write_oid(unsigned char **p, const unsigned char *start,
181 const char *oid, size_t oid_len)
182 {
183 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
184 size_t len = 0;
185
186 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start,
187 (const unsigned char *) oid, oid_len));
188 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
189 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_OID));
190
191 return (int) len;
192 }
193
mbedtls_asn1_write_algorithm_identifier(unsigned char ** p,const unsigned char * start,const char * oid,size_t oid_len,size_t par_len)194 int mbedtls_asn1_write_algorithm_identifier(unsigned char **p, const unsigned char *start,
195 const char *oid, size_t oid_len,
196 size_t par_len)
197 {
198 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
199 size_t len = 0;
200
201 if (par_len == 0) {
202 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_null(p, start));
203 } else {
204 len += par_len;
205 }
206
207 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_oid(p, start, oid, oid_len));
208
209 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
210 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start,
211 MBEDTLS_ASN1_CONSTRUCTED |
212 MBEDTLS_ASN1_SEQUENCE));
213
214 return (int) len;
215 }
216
mbedtls_asn1_write_bool(unsigned char ** p,const unsigned char * start,int boolean)217 int mbedtls_asn1_write_bool(unsigned char **p, const unsigned char *start, int boolean)
218 {
219 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
220 size_t len = 0;
221
222 if (*p - start < 1) {
223 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
224 }
225
226 *--(*p) = (boolean) ? 255 : 0;
227 len++;
228
229 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
230 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_BOOLEAN));
231
232 return (int) len;
233 }
234
asn1_write_tagged_int(unsigned char ** p,const unsigned char * start,int val,int tag)235 static int asn1_write_tagged_int(unsigned char **p, const unsigned char *start, int val, int tag)
236 {
237 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
238 size_t len = 0;
239
240 do {
241 if (*p - start < 1) {
242 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
243 }
244 len += 1;
245 *--(*p) = val & 0xff;
246 val >>= 8;
247 } while (val > 0);
248
249 if (**p & 0x80) {
250 if (*p - start < 1) {
251 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
252 }
253 *--(*p) = 0x00;
254 len += 1;
255 }
256
257 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
258 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, tag));
259
260 return (int) len;
261 }
262
mbedtls_asn1_write_int(unsigned char ** p,const unsigned char * start,int val)263 int mbedtls_asn1_write_int(unsigned char **p, const unsigned char *start, int val)
264 {
265 return asn1_write_tagged_int(p, start, val, MBEDTLS_ASN1_INTEGER);
266 }
267
mbedtls_asn1_write_enum(unsigned char ** p,const unsigned char * start,int val)268 int mbedtls_asn1_write_enum(unsigned char **p, const unsigned char *start, int val)
269 {
270 return asn1_write_tagged_int(p, start, val, MBEDTLS_ASN1_ENUMERATED);
271 }
272
mbedtls_asn1_write_tagged_string(unsigned char ** p,const unsigned char * start,int tag,const char * text,size_t text_len)273 int mbedtls_asn1_write_tagged_string(unsigned char **p, const unsigned char *start, int tag,
274 const char *text, size_t text_len)
275 {
276 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
277 size_t len = 0;
278
279 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start,
280 (const unsigned char *) text,
281 text_len));
282
283 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
284 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, tag));
285
286 return (int) len;
287 }
288
mbedtls_asn1_write_utf8_string(unsigned char ** p,const unsigned char * start,const char * text,size_t text_len)289 int mbedtls_asn1_write_utf8_string(unsigned char **p, const unsigned char *start,
290 const char *text, size_t text_len)
291 {
292 return mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_UTF8_STRING, text, text_len);
293 }
294
mbedtls_asn1_write_printable_string(unsigned char ** p,const unsigned char * start,const char * text,size_t text_len)295 int mbedtls_asn1_write_printable_string(unsigned char **p, const unsigned char *start,
296 const char *text, size_t text_len)
297 {
298 return mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_PRINTABLE_STRING, text,
299 text_len);
300 }
301
mbedtls_asn1_write_ia5_string(unsigned char ** p,const unsigned char * start,const char * text,size_t text_len)302 int mbedtls_asn1_write_ia5_string(unsigned char **p, const unsigned char *start,
303 const char *text, size_t text_len)
304 {
305 return mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_IA5_STRING, text, text_len);
306 }
307
mbedtls_asn1_write_named_bitstring(unsigned char ** p,const unsigned char * start,const unsigned char * buf,size_t bits)308 int mbedtls_asn1_write_named_bitstring(unsigned char **p,
309 const unsigned char *start,
310 const unsigned char *buf,
311 size_t bits)
312 {
313 size_t unused_bits, byte_len;
314 const unsigned char *cur_byte;
315 unsigned char cur_byte_shifted;
316 unsigned char bit;
317
318 byte_len = (bits + 7) / 8;
319 unused_bits = (byte_len * 8) - bits;
320
321 /*
322 * Named bitstrings require that trailing 0s are excluded in the encoding
323 * of the bitstring. Trailing 0s are considered part of the 'unused' bits
324 * when encoding this value in the first content octet
325 */
326 if (bits != 0) {
327 cur_byte = buf + byte_len - 1;
328 cur_byte_shifted = *cur_byte >> unused_bits;
329
330 for (;;) {
331 bit = cur_byte_shifted & 0x1;
332 cur_byte_shifted >>= 1;
333
334 if (bit != 0) {
335 break;
336 }
337
338 bits--;
339 if (bits == 0) {
340 break;
341 }
342
343 if (bits % 8 == 0) {
344 cur_byte_shifted = *--cur_byte;
345 }
346 }
347 }
348
349 return mbedtls_asn1_write_bitstring(p, start, buf, bits);
350 }
351
mbedtls_asn1_write_bitstring(unsigned char ** p,const unsigned char * start,const unsigned char * buf,size_t bits)352 int mbedtls_asn1_write_bitstring(unsigned char **p, const unsigned char *start,
353 const unsigned char *buf, size_t bits)
354 {
355 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
356 size_t len = 0;
357 size_t unused_bits, byte_len;
358
359 byte_len = (bits + 7) / 8;
360 unused_bits = (byte_len * 8) - bits;
361
362 if (*p < start || (size_t) (*p - start) < byte_len + 1) {
363 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
364 }
365
366 len = byte_len + 1;
367
368 /* Write the bitstring. Ensure the unused bits are zeroed */
369 if (byte_len > 0) {
370 byte_len--;
371 *--(*p) = buf[byte_len] & ~((0x1 << unused_bits) - 1);
372 (*p) -= byte_len;
373 memcpy(*p, buf, byte_len);
374 }
375
376 /* Write unused bits */
377 *--(*p) = (unsigned char) unused_bits;
378
379 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
380 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_BIT_STRING));
381
382 return (int) len;
383 }
384
mbedtls_asn1_write_octet_string(unsigned char ** p,const unsigned char * start,const unsigned char * buf,size_t size)385 int mbedtls_asn1_write_octet_string(unsigned char **p, const unsigned char *start,
386 const unsigned char *buf, size_t size)
387 {
388 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
389 size_t len = 0;
390
391 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start, buf, size));
392
393 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
394 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_OCTET_STRING));
395
396 return (int) len;
397 }
398
399
400 /* This is a copy of the ASN.1 parsing function mbedtls_asn1_find_named_data(),
401 * which is replicated to avoid a dependency ASN1_WRITE_C on ASN1_PARSE_C. */
asn1_find_named_data(mbedtls_asn1_named_data * list,const char * oid,size_t len)402 static mbedtls_asn1_named_data *asn1_find_named_data(
403 mbedtls_asn1_named_data *list,
404 const char *oid, size_t len)
405 {
406 while (list != NULL) {
407 if (list->oid.len == len &&
408 memcmp(list->oid.p, oid, len) == 0) {
409 break;
410 }
411
412 list = list->next;
413 }
414
415 return list;
416 }
417
mbedtls_asn1_store_named_data(mbedtls_asn1_named_data ** head,const char * oid,size_t oid_len,const unsigned char * val,size_t val_len)418 mbedtls_asn1_named_data *mbedtls_asn1_store_named_data(
419 mbedtls_asn1_named_data **head,
420 const char *oid, size_t oid_len,
421 const unsigned char *val,
422 size_t val_len)
423 {
424 mbedtls_asn1_named_data *cur;
425
426 if ((cur = asn1_find_named_data(*head, oid, oid_len)) == NULL) {
427 // Add new entry if not present yet based on OID
428 //
429 cur = (mbedtls_asn1_named_data *) mbedtls_calloc(1,
430 sizeof(mbedtls_asn1_named_data));
431 if (cur == NULL) {
432 return NULL;
433 }
434
435 cur->oid.len = oid_len;
436 cur->oid.p = mbedtls_calloc(1, oid_len);
437 if (cur->oid.p == NULL) {
438 mbedtls_free(cur);
439 return NULL;
440 }
441
442 memcpy(cur->oid.p, oid, oid_len);
443
444 cur->val.len = val_len;
445 if (val_len != 0) {
446 cur->val.p = mbedtls_calloc(1, val_len);
447 if (cur->val.p == NULL) {
448 mbedtls_free(cur->oid.p);
449 mbedtls_free(cur);
450 return NULL;
451 }
452 }
453
454 cur->next = *head;
455 *head = cur;
456 } else if (val_len == 0) {
457 mbedtls_free(cur->val.p);
458 cur->val.p = NULL;
459 } else if (cur->val.len != val_len) {
460 /*
461 * Enlarge existing value buffer if needed
462 * Preserve old data until the allocation succeeded, to leave list in
463 * a consistent state in case allocation fails.
464 */
465 void *p = mbedtls_calloc(1, val_len);
466 if (p == NULL) {
467 return NULL;
468 }
469
470 mbedtls_free(cur->val.p);
471 cur->val.p = p;
472 cur->val.len = val_len;
473 }
474
475 if (val != NULL && val_len != 0) {
476 memcpy(cur->val.p, val, val_len);
477 }
478
479 return cur;
480 }
481 #endif /* MBEDTLS_ASN1_WRITE_C */
482