der.c revision 328875
1/*- 2 * Copyright (c) 2016 Christos Zoulas 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 15 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 16 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 17 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 18 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 19 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 20 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 21 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 22 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 23 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 24 * POSSIBILITY OF SUCH DAMAGE. 25 */ 26/* 27 * DER (Distinguished Encoding Rules) Parser 28 * 29 * Sources: 30 * https://en.wikipedia.org/wiki/X.690 31 * http://fm4dd.com/openssl/certexamples.htm 32 * http://blog.engelke.com/2014/10/17/parsing-ber-and-der-encoded-asn-1-objects/ 33 */ 34#ifndef TEST_DER 35#include "file.h" 36 37#ifndef lint 38FILE_RCSID("@(#)$File: der.c,v 1.12 2017/02/10 18:14:01 christos Exp $") 39#endif 40#endif 41 42#include <sys/types.h> 43 44#include <stdio.h> 45#include <fcntl.h> 46#include <stdlib.h> 47#include <string.h> 48#include <ctype.h> 49 50#ifndef TEST_DER 51#include "magic.h" 52#include "der.h" 53#else 54#include <sys/mman.h> 55#include <sys/stat.h> 56#include <err.h> 57#endif 58 59#define DER_BAD ((uint32_t)-1) 60 61#define DER_CLASS_UNIVERSAL 0 62#define DER_CLASS_APPLICATION 1 63#define DER_CLASS_CONTEXT 2 64#define DER_CLASS_PRIVATE 3 65#ifdef DEBUG_DER 66static const char der_class[] = "UACP"; 67#endif 68 69#define DER_TYPE_PRIMITIVE 0 70#define DER_TYPE_CONSTRUCTED 1 71#ifdef DEBUG_DER 72static const char der_type[] = "PC"; 73#endif 74 75#define DER_TAG_EOC 0x00 76#define DER_TAG_BOOLEAN 0x01 77#define DER_TAG_INTEGER 0x02 78#define DER_TAG_BIT STRING 0x03 79#define DER_TAG_OCTET_STRING 0x04 80#define DER_TAG_NULL 0x05 81#define DER_TAG_OBJECT_IDENTIFIER 0x06 82#define DER_TAG_OBJECT_DESCRIPTOR 0x07 83#define DER_TAG_EXTERNAL 0x08 84#define DER_TAG_REAL 0x09 85#define DER_TAG_ENUMERATED 0x0a 86#define DER_TAG_EMBEDDED_PDV 0x0b 87#define DER_TAG_UTF8_STRING 0x0c 88#define DER_TAG_RELATIVE_OID 0x0d 89#define DER_TAG_RESERVED_1 0x0e 90#define DER_TAG_RESERVED_2 0x0f 91#define DER_TAG_SEQUENCE 0x10 92#define DER_TAG_SET 0x11 93#define DER_TAG_NUMERIC_STRING 0x12 94#define DER_TAG_PRINTABLE_STRING 0x13 95#define DER_TAG_T61_STRING 0x14 96#define DER_TAG_VIDEOTEX_STRING 0x15 97#define DER_TAG_IA5_STRING 0x16 98#define DER_TAG_UTCTIME 0x17 99#define DER_TAG_GENERALIZED_TIME 0x18 100#define DER_TAG_GRAPHIC_STRING 0x19 101#define DER_TAG_VISIBLE_STRING 0x1a 102#define DER_TAG_GENERAL_STRING 0x1b 103#define DER_TAG_UNIVERSAL_STRING 0x1c 104#define DER_TAG_CHARACTER_STRING 0x1d 105#define DER_TAG_BMP_STRING 0x1e 106#define DER_TAG_LONG 0x1f 107 108static const char *der__tag[] = { 109 "eoc", "bool", "int", "bit_str", "octet_str", 110 "null", "obj_id", "obj_desc", "ext", "real", 111 "enum", "embed", "utf8_str", "oid", "res1", 112 "res2", "seq", "set", "num_str", "prt_str", 113 "t61_str", "vid_str", "ia5_str", "utc_time", 114 "gen_time", "gr_str", "vis_str", "gen_str", 115 "char_str", "bmp_str", "long" 116}; 117 118#ifdef DEBUG_DER 119#define DPRINTF(a) printf a 120#else 121#define DPRINTF(a) 122#endif 123 124#ifdef TEST_DER 125static uint8_t 126getclass(uint8_t c) 127{ 128 return c >> 6; 129} 130 131static uint8_t 132gettype(uint8_t c) 133{ 134 return (c >> 5) & 1; 135} 136#endif 137 138static uint32_t 139gettag(const uint8_t *c, size_t *p, size_t l) 140{ 141 uint32_t tag; 142 143 if (*p >= l) 144 return DER_BAD; 145 146 tag = c[(*p)++] & 0x1f; 147 148 if (tag != 0x1f) 149 return tag; 150 151 if (*p >= l) 152 return DER_BAD; 153 154 while (c[*p] >= 0x80) { 155 tag = tag * 128 + c[(*p)++] - 0x80; 156 if (*p >= l) 157 return DER_BAD; 158 } 159 return tag; 160} 161 162/* 163 * Read the length of a DER tag from the input. 164 * 165 * `c` is the input, `p` is an output parameter that specifies how much of the 166 * input we consumed, and `l` is the maximum input length. 167 * 168 * Returns the length, or DER_BAD if the end of the input is reached or the 169 * length exceeds the remaining input. 170 */ 171static uint32_t 172getlength(const uint8_t *c, size_t *p, size_t l) 173{ 174 uint8_t digits, i; 175 size_t len; 176 int is_onebyte_result; 177 178 if (*p >= l) 179 return DER_BAD; 180 181 /* 182 * Digits can either be 0b0 followed by the result, or 0b1 183 * followed by the number of digits of the result. In either case, 184 * we verify that we can read so many bytes from the input. 185 */ 186 is_onebyte_result = (c[*p] & 0x80) == 0; 187 digits = c[(*p)++] & 0x7f; 188 if (*p + digits >= l) 189 return DER_BAD; 190 191 if (is_onebyte_result) 192 return digits; 193 194 /* 195 * Decode len. We've already verified that we're allowed to read 196 * `digits` bytes. 197 */ 198 len = 0; 199 for (i = 0; i < digits; i++) 200 len = (len << 8) | c[(*p)++]; 201 202 if (*p + len >= l) 203 return DER_BAD; 204 return CAST(uint32_t, len); 205} 206 207static const char * 208der_tag(char *buf, size_t len, uint32_t tag) 209{ 210 if (tag < DER_TAG_LONG) 211 strlcpy(buf, der__tag[tag], len); 212 else 213 snprintf(buf, len, "%#x", tag); 214 return buf; 215} 216 217#ifndef TEST_DER 218static int 219der_data(char *buf, size_t blen, uint32_t tag, const void *q, uint32_t len) 220{ 221 const uint8_t *d = CAST(const uint8_t *, q); 222 switch (tag) { 223 case DER_TAG_PRINTABLE_STRING: 224 case DER_TAG_UTF8_STRING: 225 case DER_TAG_IA5_STRING: 226 case DER_TAG_UTCTIME: 227 return snprintf(buf, blen, "%.*s", len, (const char *)q); 228 default: 229 break; 230 } 231 232 for (uint32_t i = 0; i < len; i++) { 233 uint32_t z = i << 1; 234 if (z < blen - 2) 235 snprintf(buf + z, blen - z, "%.2x", d[i]); 236 } 237 return len * 2; 238} 239 240int32_t 241der_offs(struct magic_set *ms, struct magic *m, size_t nbytes) 242{ 243 const uint8_t *b = RCAST(const uint8_t *, ms->search.s); 244 size_t offs = 0, len = ms->search.s_len ? ms->search.s_len : nbytes; 245 246 if (gettag(b, &offs, len) == DER_BAD) 247 return -1; 248 DPRINTF(("%s1: %d %zu %u\n", __func__, ms->offset, offs, m->offset)); 249 250 uint32_t tlen = getlength(b, &offs, len); 251 if (tlen == DER_BAD) 252 return -1; 253 DPRINTF(("%s2: %d %zu %u\n", __func__, ms->offset, offs, tlen)); 254 255 offs += ms->offset + m->offset; 256 DPRINTF(("cont_level = %d\n", m->cont_level)); 257#ifdef DEBUG_DER 258 for (size_t i = 0; i < m->cont_level; i++) 259 printf("cont_level[%zu] = %u\n", i, ms->c.li[i].off); 260#endif 261 if (m->cont_level != 0) { 262 if (offs + tlen > nbytes) 263 return -1; 264 ms->c.li[m->cont_level - 1].off = CAST(int, offs + tlen); 265 DPRINTF(("cont_level[%u] = %u\n", m->cont_level - 1, 266 ms->c.li[m->cont_level - 1].off)); 267 } 268 return CAST(int32_t, offs); 269} 270 271int 272der_cmp(struct magic_set *ms, struct magic *m) 273{ 274 const uint8_t *b = RCAST(const uint8_t *, ms->search.s); 275 const char *s = m->value.s; 276 size_t offs = 0, len = ms->search.s_len; 277 uint32_t tag, tlen; 278 char buf[128]; 279 280 tag = gettag(b, &offs, len); 281 if (tag == DER_BAD) 282 return -1; 283 284 tlen = getlength(b, &offs, len); 285 if (tlen == DER_BAD) 286 return -1; 287 288 der_tag(buf, sizeof(buf), tag); 289 if ((ms->flags & MAGIC_DEBUG) != 0) 290 fprintf(stderr, "%s: tag %p got=%s exp=%s\n", __func__, b, 291 buf, s); 292 size_t slen = strlen(buf); 293 294 if (strncmp(buf, s, slen) != 0) 295 return 0; 296 297 s += slen; 298 299again: 300 switch (*s) { 301 case '\0': 302 return 1; 303 case '=': 304 s++; 305 goto val; 306 default: 307 if (!isdigit((unsigned char)*s)) 308 return 0; 309 310 slen = 0; 311 do 312 slen = slen * 10 + *s - '0'; 313 while (isdigit((unsigned char)*++s)); 314 if ((ms->flags & MAGIC_DEBUG) != 0) 315 fprintf(stderr, "%s: len %zu %u\n", __func__, 316 slen, tlen); 317 if (tlen != slen) 318 return 0; 319 goto again; 320 } 321val: 322 DPRINTF(("%s: before data %zu %u\n", __func__, offs, tlen)); 323 der_data(buf, sizeof(buf), tag, b + offs, tlen); 324 if ((ms->flags & MAGIC_DEBUG) != 0) 325 fprintf(stderr, "%s: data %s %s\n", __func__, buf, s); 326 if (strcmp(buf, s) != 0 && strcmp("x", s) != 0) 327 return 0; 328 strlcpy(ms->ms_value.s, buf, sizeof(ms->ms_value.s)); 329 return 1; 330} 331#endif 332 333#ifdef TEST_DER 334static void 335printtag(uint32_t tag, const void *q, uint32_t len) 336{ 337 const uint8_t *d = q; 338 switch (tag) { 339 case DER_TAG_PRINTABLE_STRING: 340 case DER_TAG_UTF8_STRING: 341 printf("%.*s\n", len, (const char *)q); 342 return; 343 default: 344 break; 345 } 346 347 for (uint32_t i = 0; i < len; i++) 348 printf("%.2x", d[i]); 349 printf("\n"); 350} 351 352static void 353printdata(size_t level, const void *v, size_t x, size_t l) 354{ 355 const uint8_t *p = v, *ep = p + l; 356 size_t ox; 357 char buf[128]; 358 359 while (p + x < ep) { 360 const uint8_t *q; 361 uint8_t c = getclass(p[x]); 362 uint8_t t = gettype(p[x]); 363 ox = x; 364 if (x != 0) 365 printf("%.2x %.2x %.2x\n", p[x - 1], p[x], p[x + 1]); 366 uint32_t tag = gettag(p, &x, ep - p + x); 367 if (p + x >= ep) 368 break; 369 uint32_t len = getlength(p, &x, ep - p + x); 370 371 printf("%zu %zu-%zu %c,%c,%s,%u:", level, ox, x, 372 der_class[c], der_type[t], 373 der_tag(buf, sizeof(buf), tag), len); 374 q = p + x; 375 if (p + len > ep) 376 errx(EXIT_FAILURE, "corrupt der"); 377 printtag(tag, q, len); 378 if (t != DER_TYPE_PRIMITIVE) 379 printdata(level + 1, p, x, len + x); 380 x += len; 381 } 382} 383 384int 385main(int argc, char *argv[]) 386{ 387 int fd; 388 struct stat st; 389 size_t l; 390 void *p; 391 392 if ((fd = open(argv[1], O_RDONLY)) == -1) 393 err(EXIT_FAILURE, "open `%s'", argv[1]); 394 if (fstat(fd, &st) == -1) 395 err(EXIT_FAILURE, "stat `%s'", argv[1]); 396 l = (size_t)st.st_size; 397 if ((p = mmap(NULL, l, PROT_READ, MAP_FILE, fd, 0)) == MAP_FAILED) 398 err(EXIT_FAILURE, "mmap `%s'", argv[1]); 399 400 printdata(0, p, 0, l); 401 munmap(p, l); 402 return 0; 403} 404#endif 405