1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* Decoder for ASN.1 BER/DER/CER encoded bytestream 3 * 4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells@redhat.com) 6 */ 7 8 #include <linux/export.h> 9 #include <linux/kernel.h> 10 #include <linux/errno.h> 11 #include <linux/module.h> 12 #include <linux/asn1_decoder.h> 13 #include <linux/asn1_ber_bytecode.h> 14 15 static const unsigned char asn1_op_lengths[ASN1_OP__NR] = { 16 /* OPC TAG JMP ACT */ 17 [ASN1_OP_MATCH] = 1 + 1, 18 [ASN1_OP_MATCH_OR_SKIP] = 1 + 1, 19 [ASN1_OP_MATCH_ACT] = 1 + 1 + 1, 20 [ASN1_OP_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, 21 [ASN1_OP_MATCH_JUMP] = 1 + 1 + 1, 22 [ASN1_OP_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, 23 [ASN1_OP_MATCH_ANY] = 1, 24 [ASN1_OP_MATCH_ANY_OR_SKIP] = 1, 25 [ASN1_OP_MATCH_ANY_ACT] = 1 + 1, 26 [ASN1_OP_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, 27 [ASN1_OP_COND_MATCH_OR_SKIP] = 1 + 1, 28 [ASN1_OP_COND_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, 29 [ASN1_OP_COND_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, 30 [ASN1_OP_COND_MATCH_ANY] = 1, 31 [ASN1_OP_COND_MATCH_ANY_OR_SKIP] = 1, 32 [ASN1_OP_COND_MATCH_ANY_ACT] = 1 + 1, 33 [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, 34 [ASN1_OP_COND_FAIL] = 1, 35 [ASN1_OP_COMPLETE] = 1, 36 [ASN1_OP_ACT] = 1 + 1, 37 [ASN1_OP_MAYBE_ACT] = 1 + 1, 38 [ASN1_OP_RETURN] = 1, 39 [ASN1_OP_END_SEQ] = 1, 40 [ASN1_OP_END_SEQ_OF] = 1 + 1, 41 [ASN1_OP_END_SET] = 1, 42 [ASN1_OP_END_SET_OF] = 1 + 1, 43 [ASN1_OP_END_SEQ_ACT] = 1 + 1, 44 [ASN1_OP_END_SEQ_OF_ACT] = 1 + 1 + 1, 45 [ASN1_OP_END_SET_ACT] = 1 + 1, 46 [ASN1_OP_END_SET_OF_ACT] = 1 + 1 + 1, 47 }; 48 49 /* 50 * Find the length of an indefinite length object 51 * @data: The data buffer 52 * @datalen: The end of the innermost containing element in the buffer 53 * @_dp: The data parse cursor (updated before returning) 54 * @_len: Where to return the size of the element. 55 * @_errmsg: Where to return a pointer to an error message on error 56 */ 57 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen, 58 size_t *_dp, size_t *_len, 59 const char **_errmsg) 60 { 61 unsigned char tag, tmp; 62 size_t dp = *_dp, len, n; 63 int indef_level = 1; 64 65 next_tag: 66 if (unlikely(datalen - dp < 2)) { 67 if (datalen == dp) 68 goto missing_eoc; 69 goto data_overrun_error; 70 } 71 72 /* Extract a tag from the data */ 73 tag = data[dp++]; 74 if (tag == ASN1_EOC) { 75 /* It appears to be an EOC. */ 76 if (data[dp++] != 0) 77 goto invalid_eoc; 78 if (--indef_level <= 0) { 79 *_len = dp - *_dp; 80 *_dp = dp; 81 return 0; 82 } 83 goto next_tag; 84 } 85 86 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) { 87 do { 88 if (unlikely(datalen - dp < 2)) 89 goto data_overrun_error; 90 tmp = data[dp++]; 91 } while (tmp & 0x80); 92 } 93 94 /* Extract the length */ 95 len = data[dp++]; 96 if (len <= 0x7f) 97 goto check_length; 98 99 if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { 100 /* Indefinite length */ 101 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5)) 102 goto indefinite_len_primitive; 103 indef_level++; 104 goto next_tag; 105 } 106 107 n = len - 0x80; 108 if (unlikely(n > sizeof(len) - 1)) 109 goto length_too_long; 110 if (unlikely(n > datalen - dp)) 111 goto data_overrun_error; 112 len = 0; 113 for (; n > 0; n--) { 114 len <<= 8; 115 len |= data[dp++]; 116 } 117 check_length: 118 if (len > datalen - dp) 119 goto data_overrun_error; 120 dp += len; 121 goto next_tag; 122 123 length_too_long: 124 *_errmsg = "Unsupported length"; 125 goto error; 126 indefinite_len_primitive: 127 *_errmsg = "Indefinite len primitive not permitted"; 128 goto error; 129 invalid_eoc: 130 *_errmsg = "Invalid length EOC"; 131 goto error; 132 data_overrun_error: 133 *_errmsg = "Data overrun error"; 134 goto error; 135 missing_eoc: 136 *_errmsg = "Missing EOC in indefinite len cons"; 137 error: 138 *_dp = dp; 139 return -1; 140 } 141 142 /** 143 * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern 144 * @decoder: The decoder definition (produced by asn1_compiler) 145 * @context: The caller's context (to be passed to the action functions) 146 * @data: The encoded data 147 * @datalen: The size of the encoded data 148 * 149 * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern 150 * produced by asn1_compiler. Action functions are called on marked tags to 151 * allow the caller to retrieve significant data. 152 * 153 * LIMITATIONS: 154 * 155 * To keep down the amount of stack used by this function, the following limits 156 * have been imposed: 157 * 158 * (1) This won't handle datalen > 65535 without increasing the size of the 159 * cons stack elements and length_too_long checking. 160 * 161 * (2) The stack of constructed types is 10 deep. If the depth of non-leaf 162 * constructed types exceeds this, the decode will fail. 163 * 164 * (3) The SET type (not the SET OF type) isn't really supported as tracking 165 * what members of the set have been seen is a pain. 166 */ 167 int asn1_ber_decoder(const struct asn1_decoder *decoder, 168 void *context, 169 const unsigned char *data, 170 size_t datalen) 171 { 172 const unsigned char *machine = decoder->machine; 173 const asn1_action_t *actions = decoder->actions; 174 size_t machlen = decoder->machlen; 175 enum asn1_opcode op; 176 unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0; 177 const char *errmsg; 178 size_t pc = 0, dp = 0, tdp = 0, len = 0; 179 int ret; 180 181 unsigned char flags = 0; 182 #define FLAG_INDEFINITE_LENGTH 0x01 183 #define FLAG_MATCHED 0x02 184 #define FLAG_LAST_MATCHED 0x04 /* Last tag matched */ 185 #define FLAG_CONS 0x20 /* Corresponds to CONS bit in the opcode tag 186 * - ie. whether or not we are going to parse 187 * a compound type. 188 */ 189 190 #define NR_CONS_STACK 10 191 unsigned short cons_dp_stack[NR_CONS_STACK]; 192 unsigned short cons_datalen_stack[NR_CONS_STACK]; 193 unsigned char cons_hdrlen_stack[NR_CONS_STACK]; 194 #define NR_JUMP_STACK 10 195 unsigned char jump_stack[NR_JUMP_STACK]; 196 197 if (datalen > 65535) 198 return -EMSGSIZE; 199 200 next_op: 201 pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n", 202 pc, machlen, dp, datalen, csp, jsp); 203 if (unlikely(pc >= machlen)) 204 goto machine_overrun_error; 205 op = machine[pc]; 206 if (unlikely(pc + asn1_op_lengths[op] > machlen)) 207 goto machine_overrun_error; 208 209 /* If this command is meant to match a tag, then do that before 210 * evaluating the command. 211 */ 212 if (op <= ASN1_OP__MATCHES_TAG) { 213 unsigned char tmp; 214 215 /* Skip conditional matches if possible */ 216 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) || 217 (op & ASN1_OP_MATCH__SKIP && dp == datalen)) { 218 flags &= ~FLAG_LAST_MATCHED; 219 pc += asn1_op_lengths[op]; 220 goto next_op; 221 } 222 223 flags = 0; 224 hdr = 2; 225 226 /* Extract a tag from the data */ 227 if (unlikely(datalen - dp < 2)) 228 goto data_overrun_error; 229 tag = data[dp++]; 230 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) 231 goto long_tag_not_supported; 232 233 if (op & ASN1_OP_MATCH__ANY) { 234 pr_debug("- any %02x\n", tag); 235 } else { 236 /* Extract the tag from the machine 237 * - Either CONS or PRIM are permitted in the data if 238 * CONS is not set in the op stream, otherwise CONS 239 * is mandatory. 240 */ 241 optag = machine[pc + 1]; 242 flags |= optag & FLAG_CONS; 243 244 /* Determine whether the tag matched */ 245 tmp = optag ^ tag; 246 tmp &= ~(optag & ASN1_CONS_BIT); 247 pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp); 248 if (tmp != 0) { 249 /* All odd-numbered tags are MATCH_OR_SKIP. */ 250 if (op & ASN1_OP_MATCH__SKIP) { 251 pc += asn1_op_lengths[op]; 252 dp--; 253 goto next_op; 254 } 255 goto tag_mismatch; 256 } 257 } 258 flags |= FLAG_MATCHED; 259 260 len = data[dp++]; 261 if (len > 0x7f) { 262 if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { 263 /* Indefinite length */ 264 if (unlikely(!(tag & ASN1_CONS_BIT))) 265 goto indefinite_len_primitive; 266 flags |= FLAG_INDEFINITE_LENGTH; 267 if (unlikely(2 > datalen - dp)) 268 goto data_overrun_error; 269 } else { 270 int n = len - 0x80; 271 if (unlikely(n > 2)) 272 goto length_too_long; 273 if (unlikely(n > datalen - dp)) 274 goto data_overrun_error; 275 hdr += n; 276 for (len = 0; n > 0; n--) { 277 len <<= 8; 278 len |= data[dp++]; 279 } 280 if (unlikely(len > datalen - dp)) 281 goto data_overrun_error; 282 } 283 } else { 284 if (unlikely(len > datalen - dp)) 285 goto data_overrun_error; 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: 313 case ASN1_OP_MATCH_OR_SKIP: 314 case ASN1_OP_MATCH_ACT: 315 case ASN1_OP_MATCH_ACT_OR_SKIP: 316 case ASN1_OP_MATCH_ANY: 317 case ASN1_OP_MATCH_ANY_OR_SKIP: 318 case ASN1_OP_MATCH_ANY_ACT: 319 case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: 320 case ASN1_OP_COND_MATCH_OR_SKIP: 321 case ASN1_OP_COND_MATCH_ACT_OR_SKIP: 322 case ASN1_OP_COND_MATCH_ANY: 323 case ASN1_OP_COND_MATCH_ANY_OR_SKIP: 324 case ASN1_OP_COND_MATCH_ANY_ACT: 325 case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: 326 327 if (!(flags & FLAG_CONS)) { 328 if (flags & FLAG_INDEFINITE_LENGTH) { 329 size_t tmp = dp; 330 331 ret = asn1_find_indefinite_length( 332 data, datalen, &tmp, &len, &errmsg); 333 if (ret < 0) 334 goto error; 335 } 336 pr_debug("- LEAF: %zu\n", len); 337 } 338 339 if (op & ASN1_OP_MATCH__ACT) { 340 unsigned char act; 341 342 if (op & ASN1_OP_MATCH__ANY) 343 act = machine[pc + 1]; 344 else 345 act = machine[pc + 2]; 346 ret = actions[act](context, hdr, tag, data + dp, len); 347 if (ret < 0) 348 return ret; 349 } 350 351 if (!(flags & FLAG_CONS)) 352 dp += len; 353 pc += asn1_op_lengths[op]; 354 goto next_op; 355 356 case ASN1_OP_MATCH_JUMP: 357 case ASN1_OP_MATCH_JUMP_OR_SKIP: 358 case ASN1_OP_COND_MATCH_JUMP_OR_SKIP: 359 pr_debug("- MATCH_JUMP\n"); 360 if (unlikely(jsp == NR_JUMP_STACK)) 361 goto jump_stack_overflow; 362 jump_stack[jsp++] = pc + asn1_op_lengths[op]; 363 pc = machine[pc + 2]; 364 goto next_op; 365 366 case ASN1_OP_COND_FAIL: 367 if (unlikely(!(flags & FLAG_MATCHED))) 368 goto tag_mismatch; 369 pc += asn1_op_lengths[op]; 370 goto next_op; 371 372 case ASN1_OP_COMPLETE: 373 if (unlikely(jsp != 0 || csp != 0)) { 374 pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n", 375 jsp, csp); 376 return -EBADMSG; 377 } 378 return 0; 379 380 case ASN1_OP_END_SET: 381 case ASN1_OP_END_SET_ACT: 382 if (unlikely(!(flags & FLAG_MATCHED))) 383 goto tag_mismatch; 384 fallthrough; 385 386 case ASN1_OP_END_SEQ: 387 case ASN1_OP_END_SET_OF: 388 case ASN1_OP_END_SEQ_OF: 389 case ASN1_OP_END_SEQ_ACT: 390 case ASN1_OP_END_SET_OF_ACT: 391 case ASN1_OP_END_SEQ_OF_ACT: 392 if (unlikely(csp <= 0)) 393 goto cons_stack_underflow; 394 csp--; 395 tdp = cons_dp_stack[csp]; 396 hdr = cons_hdrlen_stack[csp]; 397 len = datalen; 398 datalen = cons_datalen_stack[csp]; 399 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n", 400 tdp, dp, len, datalen); 401 if (datalen == 0) { 402 /* Indefinite length - check for the EOC. */ 403 datalen = len; 404 if (unlikely(datalen - dp < 2)) 405 goto data_overrun_error; 406 if (data[dp++] != 0) { 407 if (op & ASN1_OP_END__OF) { 408 dp--; 409 csp++; 410 pc = machine[pc + 1]; 411 pr_debug("- continue\n"); 412 goto next_op; 413 } 414 goto missing_eoc; 415 } 416 if (data[dp++] != 0) 417 goto invalid_eoc; 418 len = dp - tdp - 2; 419 } else { 420 if (dp < len && (op & ASN1_OP_END__OF)) { 421 datalen = len; 422 csp++; 423 pc = machine[pc + 1]; 424 pr_debug("- continue\n"); 425 goto next_op; 426 } 427 if (dp != len) 428 goto cons_length_error; 429 len -= tdp; 430 pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp); 431 } 432 433 if (op & ASN1_OP_END__ACT) { 434 unsigned char act; 435 if (op & ASN1_OP_END__OF) 436 act = machine[pc + 2]; 437 else 438 act = machine[pc + 1]; 439 ret = actions[act](context, hdr, 0, data + tdp, len); 440 if (ret < 0) 441 return ret; 442 } 443 pc += asn1_op_lengths[op]; 444 goto next_op; 445 446 case ASN1_OP_MAYBE_ACT: 447 if (!(flags & FLAG_LAST_MATCHED)) { 448 pc += asn1_op_lengths[op]; 449 goto next_op; 450 } 451 fallthrough; 452 453 case ASN1_OP_ACT: 454 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len); 455 if (ret < 0) 456 return ret; 457 pc += asn1_op_lengths[op]; 458 goto next_op; 459 460 case ASN1_OP_RETURN: 461 if (unlikely(jsp <= 0)) 462 goto jump_stack_underflow; 463 pc = jump_stack[--jsp]; 464 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED; 465 goto next_op; 466 467 default: 468 break; 469 } 470 471 /* Shouldn't reach here */ 472 pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n", 473 op, pc); 474 return -EBADMSG; 475 476 data_overrun_error: 477 errmsg = "Data overrun error"; 478 goto error; 479 machine_overrun_error: 480 errmsg = "Machine overrun error"; 481 goto error; 482 jump_stack_underflow: 483 errmsg = "Jump stack underflow"; 484 goto error; 485 jump_stack_overflow: 486 errmsg = "Jump stack overflow"; 487 goto error; 488 cons_stack_underflow: 489 errmsg = "Cons stack underflow"; 490 goto error; 491 cons_stack_overflow: 492 errmsg = "Cons stack overflow"; 493 goto error; 494 cons_length_error: 495 errmsg = "Cons length error"; 496 goto error; 497 missing_eoc: 498 errmsg = "Missing EOC in indefinite len cons"; 499 goto error; 500 invalid_eoc: 501 errmsg = "Invalid length EOC"; 502 goto error; 503 length_too_long: 504 errmsg = "Unsupported length"; 505 goto error; 506 indefinite_len_primitive: 507 errmsg = "Indefinite len primitive not permitted"; 508 goto error; 509 tag_mismatch: 510 errmsg = "Unexpected tag"; 511 goto error; 512 long_tag_not_supported: 513 errmsg = "Long tag not supported"; 514 error: 515 pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n", 516 errmsg, pc, dp, optag, tag, len); 517 return -EBADMSG; 518 } 519 EXPORT_SYMBOL_GPL(asn1_ber_decoder); 520 521 MODULE_LICENSE("GPL"); 522