1 /* $NetBSD: der.c,v 1.7 2021/04/09 19:11:42 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 2016 Christos Zoulas 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 26 * POSSIBILITY OF SUCH DAMAGE. 27 */ 28 /* 29 * DER (Distinguished Encoding Rules) Parser 30 * 31 * Sources: 32 * https://en.wikipedia.org/wiki/X.690 33 * http://fm4dd.com/openssl/certexamples.htm 34 * http://blog.engelke.com/2014/10/17/parsing-ber-and-der-encoded-asn-1-objects/ 35 */ 36 #ifndef TEST_DER 37 #include "file.h" 38 39 #ifndef lint 40 #if 0 41 FILE_RCSID("@(#)$File: der.c,v 1.21 2020/06/15 00:58:10 christos Exp $") 42 #else 43 __RCSID("$NetBSD: der.c,v 1.7 2021/04/09 19:11:42 christos Exp $"); 44 #endif 45 #endif 46 #else 47 #define SIZE_T_FORMAT "z" 48 #define CAST(a, b) ((a)(b)) 49 #endif 50 51 #include <sys/types.h> 52 53 #include <stdio.h> 54 #include <fcntl.h> 55 #include <stdlib.h> 56 #include <string.h> 57 #include <ctype.h> 58 59 #ifndef TEST_DER 60 #include "magic.h" 61 #include "der.h" 62 #else 63 #include <sys/mman.h> 64 #include <sys/stat.h> 65 #include <err.h> 66 #endif 67 68 #define DER_BAD CAST(uint32_t, -1) 69 70 #define DER_CLASS_UNIVERSAL 0 71 #define DER_CLASS_APPLICATION 1 72 #define DER_CLASS_CONTEXT 2 73 #define DER_CLASS_PRIVATE 3 74 #if defined(DEBUG_DER) || defined(TEST_DER) 75 static const char der_class[] = "UACP"; 76 #endif 77 78 #define DER_TYPE_PRIMITIVE 0 79 #define DER_TYPE_CONSTRUCTED 1 80 #if defined(DEBUG_DER) || defined(TEST_DER) 81 static const char der_type[] = "PC"; 82 #endif 83 84 #define DER_TAG_EOC 0x00 85 #define DER_TAG_BOOLEAN 0x01 86 #define DER_TAG_INTEGER 0x02 87 #define DER_TAG_BIT STRING 0x03 88 #define DER_TAG_OCTET_STRING 0x04 89 #define DER_TAG_NULL 0x05 90 #define DER_TAG_OBJECT_IDENTIFIER 0x06 91 #define DER_TAG_OBJECT_DESCRIPTOR 0x07 92 #define DER_TAG_EXTERNAL 0x08 93 #define DER_TAG_REAL 0x09 94 #define DER_TAG_ENUMERATED 0x0a 95 #define DER_TAG_EMBEDDED_PDV 0x0b 96 #define DER_TAG_UTF8_STRING 0x0c 97 #define DER_TAG_RELATIVE_OID 0x0d 98 #define DER_TAG_TIME 0x0e 99 #define DER_TAG_RESERVED_2 0x0f 100 #define DER_TAG_SEQUENCE 0x10 101 #define DER_TAG_SET 0x11 102 #define DER_TAG_NUMERIC_STRING 0x12 103 #define DER_TAG_PRINTABLE_STRING 0x13 104 #define DER_TAG_T61_STRING 0x14 105 #define DER_TAG_VIDEOTEX_STRING 0x15 106 #define DER_TAG_IA5_STRING 0x16 107 #define DER_TAG_UTCTIME 0x17 108 #define DER_TAG_GENERALIZED_TIME 0x18 109 #define DER_TAG_GRAPHIC_STRING 0x19 110 #define DER_TAG_VISIBLE_STRING 0x1a 111 #define DER_TAG_GENERAL_STRING 0x1b 112 #define DER_TAG_UNIVERSAL_STRING 0x1c 113 #define DER_TAG_CHARACTER_STRING 0x1d 114 #define DER_TAG_BMP_STRING 0x1e 115 #define DER_TAG_DATE 0x1f 116 #define DER_TAG_TIME_OF_DAY 0x20 117 #define DER_TAG_DATE_TIME 0x21 118 #define DER_TAG_DURATION 0x22 119 #define DER_TAG_OID_IRI 0x23 120 #define DER_TAG_RELATIVE_OID_IRI 0x24 121 #define DER_TAG_LAST 0x25 122 123 static const char *der__tag[] = { 124 "eoc", "bool", "int", "bit_str", "octet_str", 125 "null", "obj_id", "obj_desc", "ext", "real", 126 "enum", "embed", "utf8_str", "rel_oid", "time", 127 "res2", "seq", "set", "num_str", "prt_str", 128 "t61_str", "vid_str", "ia5_str", "utc_time", "gen_time", 129 "gr_str", "vis_str", "gen_str", "univ_str", "char_str", 130 "bmp_str", "date", "tod", "datetime", "duration", 131 "oid-iri", "rel-oid-iri", 132 }; 133 134 #ifdef DEBUG_DER 135 #define DPRINTF(a) printf a 136 #else 137 #define DPRINTF(a) 138 #endif 139 140 #ifdef TEST_DER 141 static uint8_t 142 getclass(uint8_t c) 143 { 144 return c >> 6; 145 } 146 147 static uint8_t 148 gettype(uint8_t c) 149 { 150 return (c >> 5) & 1; 151 } 152 #endif 153 154 static uint32_t 155 gettag(const uint8_t *c, size_t *p, size_t l) 156 { 157 uint32_t tag; 158 159 if (*p >= l) 160 return DER_BAD; 161 162 tag = c[(*p)++] & 0x1f; 163 164 if (tag != 0x1f) 165 return tag; 166 167 if (*p >= l) 168 return DER_BAD; 169 170 while (c[*p] >= 0x80) { 171 tag = tag * 128 + c[(*p)++] - 0x80; 172 if (*p >= l) 173 return DER_BAD; 174 } 175 return tag; 176 } 177 178 /* 179 * Read the length of a DER tag from the input. 180 * 181 * `c` is the input, `p` is an output parameter that specifies how much of the 182 * input we consumed, and `l` is the maximum input length. 183 * 184 * Returns the length, or DER_BAD if the end of the input is reached or the 185 * length exceeds the remaining input. 186 */ 187 static uint32_t 188 getlength(const uint8_t *c, size_t *p, size_t l) 189 { 190 uint8_t digits, i; 191 size_t len; 192 int is_onebyte_result; 193 194 if (*p >= l) { 195 DPRINTF(("%s:[1] %zu >= %zu\n", __func__, *p, l)); 196 return DER_BAD; 197 } 198 199 /* 200 * Digits can either be 0b0 followed by the result, or 0b1 201 * followed by the number of digits of the result. In either case, 202 * we verify that we can read so many bytes from the input. 203 */ 204 is_onebyte_result = (c[*p] & 0x80) == 0; 205 digits = c[(*p)++] & 0x7f; 206 if (*p + digits >= l) { 207 DPRINTF(("%s:[2] %zu + %u >= %zu\n", __func__, *p, digits, l)); 208 return DER_BAD; 209 } 210 211 if (is_onebyte_result) 212 return digits; 213 214 /* 215 * Decode len. We've already verified that we're allowed to read 216 * `digits` bytes. 217 */ 218 len = 0; 219 for (i = 0; i < digits; i++) 220 len = (len << 8) | c[(*p)++]; 221 222 if (len > UINT32_MAX - *p || *p + len > l) { 223 DPRINTF(("%s:[3] bad len %zu + %zu >= %zu\n", 224 __func__, *p, len, l)); 225 return DER_BAD; 226 } 227 return CAST(uint32_t, len); 228 } 229 230 static const char * 231 der_tag(char *buf, size_t len, uint32_t tag) 232 { 233 if (tag < DER_TAG_LAST) 234 strlcpy(buf, der__tag[tag], len); 235 else 236 snprintf(buf, len, "%#x", tag); 237 return buf; 238 } 239 240 #ifndef TEST_DER 241 static int 242 der_data(char *buf, size_t blen, uint32_t tag, const void *q, uint32_t len) 243 { 244 const uint8_t *d = CAST(const uint8_t *, q); 245 switch (tag) { 246 case DER_TAG_PRINTABLE_STRING: 247 case DER_TAG_UTF8_STRING: 248 case DER_TAG_IA5_STRING: 249 return snprintf(buf, blen, "%.*s", len, RCAST(const char *, q)); 250 case DER_TAG_UTCTIME: 251 if (len < 12) 252 break; 253 return snprintf(buf, blen, 254 "20%c%c-%c%c-%c%c %c%c:%c%c:%c%c GMT", d[0], d[1], d[2], 255 d[3], d[4], d[5], d[6], d[7], d[8], d[9], d[10], d[11]); 256 default: 257 break; 258 } 259 260 for (uint32_t i = 0; i < len; i++) { 261 uint32_t z = i << 1; 262 if (z < blen - 2) 263 snprintf(buf + z, blen - z, "%.2x", d[i]); 264 } 265 return len * 2; 266 } 267 268 int32_t 269 der_offs(struct magic_set *ms, struct magic *m, size_t nbytes) 270 { 271 const uint8_t *b = RCAST(const uint8_t *, ms->search.s); 272 size_t offs = 0, len = ms->search.s_len ? ms->search.s_len : nbytes; 273 274 if (gettag(b, &offs, len) == DER_BAD) { 275 DPRINTF(("%s: bad tag 1\n", __func__)); 276 return -1; 277 } 278 DPRINTF(("%s1: %d %" SIZE_T_FORMAT "u %u\n", __func__, ms->offset, 279 offs, m->offset)); 280 281 uint32_t tlen = getlength(b, &offs, len); 282 if (tlen == DER_BAD) { 283 DPRINTF(("%s: bad tag 2\n", __func__)); 284 return -1; 285 } 286 DPRINTF(("%s2: %d %" SIZE_T_FORMAT "u %u\n", __func__, ms->offset, 287 offs, tlen)); 288 289 offs += ms->offset + m->offset; 290 DPRINTF(("cont_level = %d\n", m->cont_level)); 291 #ifdef DEBUG_DER 292 for (size_t i = 0; i < m->cont_level; i++) 293 printf("cont_level[%" SIZE_T_FORMAT "u] = %u\n", i, 294 ms->c.li[i].off); 295 #endif 296 if (m->cont_level != 0) { 297 if (offs + tlen > nbytes) 298 return -1; 299 ms->c.li[m->cont_level - 1].off = CAST(int, offs + tlen); 300 DPRINTF(("cont_level[%u] = %u\n", m->cont_level - 1, 301 ms->c.li[m->cont_level - 1].off)); 302 } 303 return CAST(int32_t, offs); 304 } 305 306 int 307 der_cmp(struct magic_set *ms, struct magic *m) 308 { 309 const uint8_t *b = RCAST(const uint8_t *, ms->search.s); 310 const char *s = m->value.s; 311 size_t offs = 0, len = ms->search.s_len; 312 uint32_t tag, tlen; 313 char buf[128]; 314 315 DPRINTF(("%s: compare %zu bytes\n", __func__, len)); 316 317 tag = gettag(b, &offs, len); 318 if (tag == DER_BAD) { 319 DPRINTF(("%s: bad tag 1\n", __func__)); 320 return -1; 321 } 322 323 DPRINTF(("%s1: %d %" SIZE_T_FORMAT "u %u\n", __func__, ms->offset, 324 offs, m->offset)); 325 326 tlen = getlength(b, &offs, len); 327 if (tlen == DER_BAD) { 328 DPRINTF(("%s: bad tag 2\n", __func__)); 329 return -1; 330 } 331 332 der_tag(buf, sizeof(buf), tag); 333 if ((ms->flags & MAGIC_DEBUG) != 0) 334 fprintf(stderr, "%s: tag %p got=%s exp=%s\n", __func__, b, 335 buf, s); 336 size_t slen = strlen(buf); 337 338 if (strncmp(buf, s, slen) != 0) 339 return 0; 340 341 s += slen; 342 343 again: 344 switch (*s) { 345 case '\0': 346 return 1; 347 case '=': 348 s++; 349 goto val; 350 default: 351 if (!isdigit(CAST(unsigned char, *s))) 352 return 0; 353 354 slen = 0; 355 do 356 slen = slen * 10 + *s - '0'; 357 while (isdigit(CAST(unsigned char, *++s))); 358 if ((ms->flags & MAGIC_DEBUG) != 0) 359 fprintf(stderr, "%s: len %" SIZE_T_FORMAT "u %u\n", 360 __func__, slen, tlen); 361 if (tlen != slen) 362 return 0; 363 goto again; 364 } 365 val: 366 DPRINTF(("%s: before data %" SIZE_T_FORMAT "u %u\n", __func__, offs, 367 tlen)); 368 der_data(buf, sizeof(buf), tag, b + offs, tlen); 369 if ((ms->flags & MAGIC_DEBUG) != 0) 370 fprintf(stderr, "%s: data %s %s\n", __func__, buf, s); 371 if (strcmp(buf, s) != 0 && strcmp("x", s) != 0) 372 return 0; 373 strlcpy(ms->ms_value.s, buf, sizeof(ms->ms_value.s)); 374 return 1; 375 } 376 #endif 377 378 #ifdef TEST_DER 379 static void 380 printtag(uint32_t tag, const void *q, uint32_t len) 381 { 382 const uint8_t *d = q; 383 switch (tag) { 384 case DER_TAG_PRINTABLE_STRING: 385 case DER_TAG_UTF8_STRING: 386 case DER_TAG_IA5_STRING: 387 case DER_TAG_UTCTIME: 388 printf("%.*s\n", len, (const char *)q); 389 return; 390 default: 391 break; 392 } 393 394 for (uint32_t i = 0; i < len; i++) 395 printf("%.2x", d[i]); 396 printf("\n"); 397 } 398 399 static void 400 printdata(size_t level, const void *v, size_t x, size_t l) 401 { 402 const uint8_t *p = v, *ep = p + l; 403 size_t ox; 404 char buf[128]; 405 406 while (p + x < ep) { 407 const uint8_t *q; 408 uint8_t c = getclass(p[x]); 409 uint8_t t = gettype(p[x]); 410 ox = x; 411 // if (x != 0) 412 // printf("%.2x %.2x %.2x\n", p[x - 1], p[x], p[x + 1]); 413 uint32_t tag = gettag(p, &x, ep - p + x); 414 if (p + x >= ep) 415 break; 416 uint32_t len = getlength(p, &x, ep - p + x); 417 418 printf("%" SIZE_T_FORMAT "u %" SIZE_T_FORMAT "u-%" 419 SIZE_T_FORMAT "u %c,%c,%s,%u:", level, ox, x, 420 der_class[c], der_type[t], 421 der_tag(buf, sizeof(buf), tag), len); 422 q = p + x; 423 if (p + len > ep) 424 errx(EXIT_FAILURE, "corrupt der"); 425 printtag(tag, q, len); 426 if (t != DER_TYPE_PRIMITIVE) 427 printdata(level + 1, p, x, len + x); 428 x += len; 429 } 430 } 431 432 int 433 main(int argc, char *argv[]) 434 { 435 int fd; 436 struct stat st; 437 size_t l; 438 void *p; 439 440 if ((fd = open(argv[1], O_RDONLY)) == -1) 441 err(EXIT_FAILURE, "open `%s'", argv[1]); 442 if (fstat(fd, &st) == -1) 443 err(EXIT_FAILURE, "stat `%s'", argv[1]); 444 l = (size_t)st.st_size; 445 if ((p = mmap(NULL, l, PROT_READ, MAP_FILE, fd, 0)) == MAP_FAILED) 446 err(EXIT_FAILURE, "mmap `%s'", argv[1]); 447 448 printdata(0, p, 0, l); 449 munmap(p, l); 450 return 0; 451 } 452 #endif 453