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