1 /* Decoder for ASN.1 BER/DER/CER encoded bytestream 2 * 3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. 4 * Written by David Howells (dhowells@redhat.com) 5 * 6 * This program is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU General Public Licence 8 * as published by the Free Software Foundation; either version 9 * 2 of the Licence, or (at your option) any later version. 10 */ 11 12 #include <linux/export.h> 13 #include <linux/kernel.h> 14 #include <linux/errno.h> 15 #include <linux/asn1_decoder.h> 16 #include <linux/asn1_ber_bytecode.h> 17 18 static const unsigned char asn1_op_lengths[ASN1_OP__NR] = { 19 /* OPC TAG JMP ACT */ 20 [ASN1_OP_MATCH] = 1 + 1, 21 [ASN1_OP_MATCH_OR_SKIP] = 1 + 1, 22 [ASN1_OP_MATCH_ACT] = 1 + 1 + 1, 23 [ASN1_OP_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, 24 [ASN1_OP_MATCH_JUMP] = 1 + 1 + 1, 25 [ASN1_OP_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, 26 [ASN1_OP_MATCH_ANY] = 1, 27 [ASN1_OP_MATCH_ANY_OR_SKIP] = 1, 28 [ASN1_OP_MATCH_ANY_ACT] = 1 + 1, 29 [ASN1_OP_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, 30 [ASN1_OP_COND_MATCH_OR_SKIP] = 1 + 1, 31 [ASN1_OP_COND_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, 32 [ASN1_OP_COND_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, 33 [ASN1_OP_COND_MATCH_ANY] = 1, 34 [ASN1_OP_COND_MATCH_ANY_OR_SKIP] = 1, 35 [ASN1_OP_COND_MATCH_ANY_ACT] = 1 + 1, 36 [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, 37 [ASN1_OP_COND_FAIL] = 1, 38 [ASN1_OP_COMPLETE] = 1, 39 [ASN1_OP_ACT] = 1 + 1, 40 [ASN1_OP_MAYBE_ACT] = 1 + 1, 41 [ASN1_OP_RETURN] = 1, 42 [ASN1_OP_END_SEQ] = 1, 43 [ASN1_OP_END_SEQ_OF] = 1 + 1, 44 [ASN1_OP_END_SET] = 1, 45 [ASN1_OP_END_SET_OF] = 1 + 1, 46 [ASN1_OP_END_SEQ_ACT] = 1 + 1, 47 [ASN1_OP_END_SEQ_OF_ACT] = 1 + 1 + 1, 48 [ASN1_OP_END_SET_ACT] = 1 + 1, 49 [ASN1_OP_END_SET_OF_ACT] = 1 + 1 + 1, 50 }; 51 52 /* 53 * Find the length of an indefinite length object 54 * @data: The data buffer 55 * @datalen: The end of the innermost containing element in the buffer 56 * @_dp: The data parse cursor (updated before returning) 57 * @_len: Where to return the size of the element. 58 * @_errmsg: Where to return a pointer to an error message on error 59 */ 60 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen, 61 size_t *_dp, size_t *_len, 62 const char **_errmsg) 63 { 64 unsigned char tag, tmp; 65 size_t dp = *_dp, len, n; 66 int indef_level = 1; 67 68 next_tag: 69 if (unlikely(datalen - dp < 2)) { 70 if (datalen == dp) 71 goto missing_eoc; 72 goto data_overrun_error; 73 } 74 75 /* Extract a tag from the data */ 76 tag = data[dp++]; 77 if (tag == ASN1_EOC) { 78 /* It appears to be an EOC. */ 79 if (data[dp++] != 0) 80 goto invalid_eoc; 81 if (--indef_level <= 0) { 82 *_len = dp - *_dp; 83 *_dp = dp; 84 return 0; 85 } 86 goto next_tag; 87 } 88 89 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) { 90 do { 91 if (unlikely(datalen - dp < 2)) 92 goto data_overrun_error; 93 tmp = data[dp++]; 94 } while (tmp & 0x80); 95 } 96 97 /* Extract the length */ 98 len = data[dp++]; 99 if (len <= 0x7f) 100 goto check_length; 101 102 if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { 103 /* Indefinite length */ 104 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5)) 105 goto indefinite_len_primitive; 106 indef_level++; 107 goto next_tag; 108 } 109 110 n = len - 0x80; 111 if (unlikely(n > sizeof(len) - 1)) 112 goto length_too_long; 113 if (unlikely(n > datalen - dp)) 114 goto data_overrun_error; 115 len = 0; 116 for (; n > 0; n--) { 117 len <<= 8; 118 len |= data[dp++]; 119 } 120 check_length: 121 if (len > datalen - dp) 122 goto data_overrun_error; 123 dp += len; 124 goto next_tag; 125 126 length_too_long: 127 *_errmsg = "Unsupported length"; 128 goto error; 129 indefinite_len_primitive: 130 *_errmsg = "Indefinite len primitive not permitted"; 131 goto error; 132 invalid_eoc: 133 *_errmsg = "Invalid length EOC"; 134 goto error; 135 data_overrun_error: 136 *_errmsg = "Data overrun error"; 137 goto error; 138 missing_eoc: 139 *_errmsg = "Missing EOC in indefinite len cons"; 140 error: 141 *_dp = dp; 142 return -1; 143 } 144 145 /** 146 * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern 147 * @decoder: The decoder definition (produced by asn1_compiler) 148 * @context: The caller's context (to be passed to the action functions) 149 * @data: The encoded data 150 * @datalen: The size of the encoded data 151 * 152 * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern 153 * produced by asn1_compiler. Action functions are called on marked tags to 154 * allow the caller to retrieve significant data. 155 * 156 * LIMITATIONS: 157 * 158 * To keep down the amount of stack used by this function, the following limits 159 * have been imposed: 160 * 161 * (1) This won't handle datalen > 65535 without increasing the size of the 162 * cons stack elements and length_too_long checking. 163 * 164 * (2) The stack of constructed types is 10 deep. If the depth of non-leaf 165 * constructed types exceeds this, the decode will fail. 166 * 167 * (3) The SET type (not the SET OF type) isn't really supported as tracking 168 * what members of the set have been seen is a pain. 169 */ 170 int asn1_ber_decoder(const struct asn1_decoder *decoder, 171 void *context, 172 const unsigned char *data, 173 size_t datalen) 174 { 175 const unsigned char *machine = decoder->machine; 176 const asn1_action_t *actions = decoder->actions; 177 size_t machlen = decoder->machlen; 178 enum asn1_opcode op; 179 unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0; 180 const char *errmsg; 181 size_t pc = 0, dp = 0, tdp = 0, len = 0; 182 int ret; 183 184 unsigned char flags = 0; 185 #define FLAG_INDEFINITE_LENGTH 0x01 186 #define FLAG_MATCHED 0x02 187 #define FLAG_LAST_MATCHED 0x04 /* Last tag matched */ 188 #define FLAG_CONS 0x20 /* Corresponds to CONS bit in the opcode tag 189 * - ie. whether or not we are going to parse 190 * a compound type. 191 */ 192 193 #define NR_CONS_STACK 10 194 unsigned short cons_dp_stack[NR_CONS_STACK]; 195 unsigned short cons_datalen_stack[NR_CONS_STACK]; 196 unsigned char cons_hdrlen_stack[NR_CONS_STACK]; 197 #define NR_JUMP_STACK 10 198 unsigned char jump_stack[NR_JUMP_STACK]; 199 200 if (datalen > 65535) 201 return -EMSGSIZE; 202 203 next_op: 204 pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n", 205 pc, machlen, dp, datalen, csp, jsp); 206 if (unlikely(pc >= machlen)) 207 goto machine_overrun_error; 208 op = machine[pc]; 209 if (unlikely(pc + asn1_op_lengths[op] > machlen)) 210 goto machine_overrun_error; 211 212 /* If this command is meant to match a tag, then do that before 213 * evaluating the command. 214 */ 215 if (op <= ASN1_OP__MATCHES_TAG) { 216 unsigned char tmp; 217 218 /* Skip conditional matches if possible */ 219 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) || 220 (op & ASN1_OP_MATCH__SKIP && dp == datalen)) { 221 flags &= ~FLAG_LAST_MATCHED; 222 pc += asn1_op_lengths[op]; 223 goto next_op; 224 } 225 226 flags = 0; 227 hdr = 2; 228 229 /* Extract a tag from the data */ 230 if (unlikely(dp >= datalen - 1)) 231 goto data_overrun_error; 232 tag = data[dp++]; 233 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) 234 goto long_tag_not_supported; 235 236 if (op & ASN1_OP_MATCH__ANY) { 237 pr_debug("- any %02x\n", tag); 238 } else { 239 /* Extract the tag from the machine 240 * - Either CONS or PRIM are permitted in the data if 241 * CONS is not set in the op stream, otherwise CONS 242 * is mandatory. 243 */ 244 optag = machine[pc + 1]; 245 flags |= optag & FLAG_CONS; 246 247 /* Determine whether the tag matched */ 248 tmp = optag ^ tag; 249 tmp &= ~(optag & ASN1_CONS_BIT); 250 pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp); 251 if (tmp != 0) { 252 /* All odd-numbered tags are MATCH_OR_SKIP. */ 253 if (op & ASN1_OP_MATCH__SKIP) { 254 pc += asn1_op_lengths[op]; 255 dp--; 256 goto next_op; 257 } 258 goto tag_mismatch; 259 } 260 } 261 flags |= FLAG_MATCHED; 262 263 len = data[dp++]; 264 if (len > 0x7f) { 265 if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { 266 /* Indefinite length */ 267 if (unlikely(!(tag & ASN1_CONS_BIT))) 268 goto indefinite_len_primitive; 269 flags |= FLAG_INDEFINITE_LENGTH; 270 if (unlikely(2 > datalen - dp)) 271 goto data_overrun_error; 272 } else { 273 int n = len - 0x80; 274 if (unlikely(n > 2)) 275 goto length_too_long; 276 if (unlikely(dp >= datalen - n)) 277 goto data_overrun_error; 278 hdr += n; 279 for (len = 0; n > 0; n--) { 280 len <<= 8; 281 len |= data[dp++]; 282 } 283 if (unlikely(len > datalen - dp)) 284 goto data_overrun_error; 285 } 286 } 287 288 if (flags & FLAG_CONS) { 289 /* For expected compound forms, we stack the positions 290 * of the start and end of the data. 291 */ 292 if (unlikely(csp >= NR_CONS_STACK)) 293 goto cons_stack_overflow; 294 cons_dp_stack[csp] = dp; 295 cons_hdrlen_stack[csp] = hdr; 296 if (!(flags & FLAG_INDEFINITE_LENGTH)) { 297 cons_datalen_stack[csp] = datalen; 298 datalen = dp + len; 299 } else { 300 cons_datalen_stack[csp] = 0; 301 } 302 csp++; 303 } 304 305 pr_debug("- TAG: %02x %zu%s\n", 306 tag, len, flags & FLAG_CONS ? " CONS" : ""); 307 tdp = dp; 308 } 309 310 /* Decide how to handle the operation */ 311 switch (op) { 312 case ASN1_OP_MATCH_ANY_ACT: 313 case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: 314 case ASN1_OP_COND_MATCH_ANY_ACT: 315 case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: 316 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len); 317 if (ret < 0) 318 return ret; 319 goto skip_data; 320 321 case ASN1_OP_MATCH_ACT: 322 case ASN1_OP_MATCH_ACT_OR_SKIP: 323 case ASN1_OP_COND_MATCH_ACT_OR_SKIP: 324 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len); 325 if (ret < 0) 326 return ret; 327 goto skip_data; 328 329 case ASN1_OP_MATCH: 330 case ASN1_OP_MATCH_OR_SKIP: 331 case ASN1_OP_MATCH_ANY: 332 case ASN1_OP_MATCH_ANY_OR_SKIP: 333 case ASN1_OP_COND_MATCH_OR_SKIP: 334 case ASN1_OP_COND_MATCH_ANY: 335 case ASN1_OP_COND_MATCH_ANY_OR_SKIP: 336 skip_data: 337 if (!(flags & FLAG_CONS)) { 338 if (flags & FLAG_INDEFINITE_LENGTH) { 339 ret = asn1_find_indefinite_length( 340 data, datalen, &dp, &len, &errmsg); 341 if (ret < 0) 342 goto error; 343 } else { 344 dp += len; 345 } 346 pr_debug("- LEAF: %zu\n", len); 347 } 348 pc += asn1_op_lengths[op]; 349 goto next_op; 350 351 case ASN1_OP_MATCH_JUMP: 352 case ASN1_OP_MATCH_JUMP_OR_SKIP: 353 case ASN1_OP_COND_MATCH_JUMP_OR_SKIP: 354 pr_debug("- MATCH_JUMP\n"); 355 if (unlikely(jsp == NR_JUMP_STACK)) 356 goto jump_stack_overflow; 357 jump_stack[jsp++] = pc + asn1_op_lengths[op]; 358 pc = machine[pc + 2]; 359 goto next_op; 360 361 case ASN1_OP_COND_FAIL: 362 if (unlikely(!(flags & FLAG_MATCHED))) 363 goto tag_mismatch; 364 pc += asn1_op_lengths[op]; 365 goto next_op; 366 367 case ASN1_OP_COMPLETE: 368 if (unlikely(jsp != 0 || csp != 0)) { 369 pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n", 370 jsp, csp); 371 return -EBADMSG; 372 } 373 return 0; 374 375 case ASN1_OP_END_SET: 376 case ASN1_OP_END_SET_ACT: 377 if (unlikely(!(flags & FLAG_MATCHED))) 378 goto tag_mismatch; 379 case ASN1_OP_END_SEQ: 380 case ASN1_OP_END_SET_OF: 381 case ASN1_OP_END_SEQ_OF: 382 case ASN1_OP_END_SEQ_ACT: 383 case ASN1_OP_END_SET_OF_ACT: 384 case ASN1_OP_END_SEQ_OF_ACT: 385 if (unlikely(csp <= 0)) 386 goto cons_stack_underflow; 387 csp--; 388 tdp = cons_dp_stack[csp]; 389 hdr = cons_hdrlen_stack[csp]; 390 len = datalen; 391 datalen = cons_datalen_stack[csp]; 392 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n", 393 tdp, dp, len, datalen); 394 if (datalen == 0) { 395 /* Indefinite length - check for the EOC. */ 396 datalen = len; 397 if (unlikely(datalen - dp < 2)) 398 goto data_overrun_error; 399 if (data[dp++] != 0) { 400 if (op & ASN1_OP_END__OF) { 401 dp--; 402 csp++; 403 pc = machine[pc + 1]; 404 pr_debug("- continue\n"); 405 goto next_op; 406 } 407 goto missing_eoc; 408 } 409 if (data[dp++] != 0) 410 goto invalid_eoc; 411 len = dp - tdp - 2; 412 } else { 413 if (dp < len && (op & ASN1_OP_END__OF)) { 414 datalen = len; 415 csp++; 416 pc = machine[pc + 1]; 417 pr_debug("- continue\n"); 418 goto next_op; 419 } 420 if (dp != len) 421 goto cons_length_error; 422 len -= tdp; 423 pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp); 424 } 425 426 if (op & ASN1_OP_END__ACT) { 427 unsigned char act; 428 if (op & ASN1_OP_END__OF) 429 act = machine[pc + 2]; 430 else 431 act = machine[pc + 1]; 432 ret = actions[act](context, hdr, 0, data + tdp, len); 433 } 434 pc += asn1_op_lengths[op]; 435 goto next_op; 436 437 case ASN1_OP_MAYBE_ACT: 438 if (!(flags & FLAG_LAST_MATCHED)) { 439 pc += asn1_op_lengths[op]; 440 goto next_op; 441 } 442 case ASN1_OP_ACT: 443 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len); 444 if (ret < 0) 445 return ret; 446 pc += asn1_op_lengths[op]; 447 goto next_op; 448 449 case ASN1_OP_RETURN: 450 if (unlikely(jsp <= 0)) 451 goto jump_stack_underflow; 452 pc = jump_stack[--jsp]; 453 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED; 454 goto next_op; 455 456 default: 457 break; 458 } 459 460 /* Shouldn't reach here */ 461 pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n", 462 op, pc); 463 return -EBADMSG; 464 465 data_overrun_error: 466 errmsg = "Data overrun error"; 467 goto error; 468 machine_overrun_error: 469 errmsg = "Machine overrun error"; 470 goto error; 471 jump_stack_underflow: 472 errmsg = "Jump stack underflow"; 473 goto error; 474 jump_stack_overflow: 475 errmsg = "Jump stack overflow"; 476 goto error; 477 cons_stack_underflow: 478 errmsg = "Cons stack underflow"; 479 goto error; 480 cons_stack_overflow: 481 errmsg = "Cons stack overflow"; 482 goto error; 483 cons_length_error: 484 errmsg = "Cons length error"; 485 goto error; 486 missing_eoc: 487 errmsg = "Missing EOC in indefinite len cons"; 488 goto error; 489 invalid_eoc: 490 errmsg = "Invalid length EOC"; 491 goto error; 492 length_too_long: 493 errmsg = "Unsupported length"; 494 goto error; 495 indefinite_len_primitive: 496 errmsg = "Indefinite len primitive not permitted"; 497 goto error; 498 tag_mismatch: 499 errmsg = "Unexpected tag"; 500 goto error; 501 long_tag_not_supported: 502 errmsg = "Long tag not supported"; 503 error: 504 pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n", 505 errmsg, pc, dp, optag, tag, len); 506 return -EBADMSG; 507 } 508 EXPORT_SYMBOL_GPL(asn1_ber_decoder); 509