lib/asn1_decoder.c

   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/module.h>
  16 #include <linux/asn1_decoder.h>
  17 #include <linux/asn1_ber_bytecode.h>
  18
  19 static const unsigned char asn1_op_lengths[ASN1_OP__NR] = {
  20         /*                                      OPC TAG JMP ACT */
  21         [ASN1_OP_MATCH]                         = 1 + 1,
  22         [ASN1_OP_MATCH_OR_SKIP]                 = 1 + 1,
  23         [ASN1_OP_MATCH_ACT]                     = 1 + 1     + 1,
  24         [ASN1_OP_MATCH_ACT_OR_SKIP]             = 1 + 1     + 1,
  25         [ASN1_OP_MATCH_JUMP]                    = 1 + 1 + 1,
  26         [ASN1_OP_MATCH_JUMP_OR_SKIP]            = 1 + 1 + 1,
  27         [ASN1_OP_MATCH_ANY]                     = 1,
  28         [ASN1_OP_MATCH_ANY_OR_SKIP]             = 1,
  29         [ASN1_OP_MATCH_ANY_ACT]                 = 1         + 1,
  30         [ASN1_OP_MATCH_ANY_ACT_OR_SKIP]         = 1         + 1,
  31         [ASN1_OP_COND_MATCH_OR_SKIP]            = 1 + 1,
  32         [ASN1_OP_COND_MATCH_ACT_OR_SKIP]        = 1 + 1     + 1,
  33         [ASN1_OP_COND_MATCH_JUMP_OR_SKIP]       = 1 + 1 + 1,
  34         [ASN1_OP_COND_MATCH_ANY]                = 1,
  35         [ASN1_OP_COND_MATCH_ANY_OR_SKIP]        = 1,
  36         [ASN1_OP_COND_MATCH_ANY_ACT]            = 1         + 1,
  37         [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]    = 1         + 1,
  38         [ASN1_OP_COND_FAIL]                     = 1,
  39         [ASN1_OP_COMPLETE]                      = 1,
  40         [ASN1_OP_ACT]                           = 1         + 1,
  41         [ASN1_OP_MAYBE_ACT]                     = 1         + 1,
  42         [ASN1_OP_RETURN]                        = 1,
  43         [ASN1_OP_END_SEQ]                       = 1,
  44         [ASN1_OP_END_SEQ_OF]                    = 1     + 1,
  45         [ASN1_OP_END_SET]                       = 1,
  46         [ASN1_OP_END_SET_OF]                    = 1     + 1,
  47         [ASN1_OP_END_SEQ_ACT]                   = 1         + 1,
  48         [ASN1_OP_END_SEQ_OF_ACT]                = 1     + 1 + 1,
  49         [ASN1_OP_END_SET_ACT]                   = 1         + 1,
  50         [ASN1_OP_END_SET_OF_ACT]                = 1     + 1 + 1,
  51 };
  52
  53 /*
  54  * Find the length of an indefinite length object
  55  * @data: The data buffer
  56  * @datalen: The end of the innermost containing element in the buffer
  57  * @_dp: The data parse cursor (updated before returning)
  58  * @_len: Where to return the size of the element.
  59  * @_errmsg: Where to return a pointer to an error message on error
  60  */
  61 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
  62                                        size_t *_dp, size_t *_len,
  63                                        const char **_errmsg)
  64 {
  65         unsigned char tag, tmp;
  66         size_t dp = *_dp, len, n;
  67         int indef_level = 1;
  68
  69 next_tag:
  70         if (unlikely(datalen - dp < 2)) {
  71                 if (datalen == dp)
  72                         goto missing_eoc;
  73                 goto data_overrun_error;
  74         }
  75
  76         /* Extract a tag from the data */
  77         tag = data[dp++];
  78         if (tag == ASN1_EOC) {
  79                 /* It appears to be an EOC. */
  80                 if (data[dp++] != 0)
  81                         goto invalid_eoc;
  82                 if (--indef_level <= 0) {
  83                         *_len = dp - *_dp;
  84                         *_dp = dp;
  85                         return 0;
  86                 }
  87                 goto next_tag;
  88         }
  89
  90         if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
  91                 do {
  92                         if (unlikely(datalen - dp < 2))
  93                                 goto data_overrun_error;
  94                         tmp = data[dp++];
  95                 } while (tmp & 0x80);
  96         }
  97
  98         /* Extract the length */
  99         len = data[dp++];
 100         if (len <= 0x7f)
 101                 goto check_length;
 102
 103         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 104                 /* Indefinite length */
 105                 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
 106                         goto indefinite_len_primitive;
 107                 indef_level++;
 108                 goto next_tag;
 109         }
 110
 111         n = len - 0x80;
 112         if (unlikely(n > sizeof(len) - 1))
 113                 goto length_too_long;
 114         if (unlikely(n > datalen - dp))
 115                 goto data_overrun_error;
 116         len = 0;
 117         for (; n > 0; n--) {
 118                 len <<= 8;
 119                 len |= data[dp++];
 120         }
 121 check_length:
 122         if (len > datalen - dp)
 123                 goto data_overrun_error;
 124         dp += len;
 125         goto next_tag;
 126
 127 length_too_long:
 128         *_errmsg = "Unsupported length";
 129         goto error;
 130 indefinite_len_primitive:
 131         *_errmsg = "Indefinite len primitive not permitted";
 132         goto error;
 133 invalid_eoc:
 134         *_errmsg = "Invalid length EOC";
 135         goto error;
 136 data_overrun_error:
 137         *_errmsg = "Data overrun error";
 138         goto error;
 139 missing_eoc:
 140         *_errmsg = "Missing EOC in indefinite len cons";
 141 error:
 142         *_dp = dp;
 143         return -1;
 144 }
 145
 146 /**
 147  * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
 148  * @decoder: The decoder definition (produced by asn1_compiler)
 149  * @context: The caller's context (to be passed to the action functions)
 150  * @data: The encoded data
 151  * @datalen: The size of the encoded data
 152  *
 153  * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
 154  * produced by asn1_compiler.  Action functions are called on marked tags to
 155  * allow the caller to retrieve significant data.
 156  *
 157  * LIMITATIONS:
 158  *
 159  * To keep down the amount of stack used by this function, the following limits
 160  * have been imposed:
 161  *
 162  *  (1) This won't handle datalen > 65535 without increasing the size of the
 163  *      cons stack elements and length_too_long checking.
 164  *
 165  *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
 166  *      constructed types exceeds this, the decode will fail.
 167  *
 168  *  (3) The SET type (not the SET OF type) isn't really supported as tracking
 169  *      what members of the set have been seen is a pain.
 170  */
 171 int asn1_ber_decoder(const struct asn1_decoder *decoder,
 172                      void *context,
 173                      const unsigned char *data,
 174                      size_t datalen)
 175 {
 176         const unsigned char *machine = decoder->machine;
 177         const asn1_action_t *actions = decoder->actions;
 178         size_t machlen = decoder->machlen;
 179         enum asn1_opcode op;
 180         unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
 181         const char *errmsg;
 182         size_t pc = 0, dp = 0, tdp = 0, len = 0;
 183         int ret;
 184
 185         unsigned char flags = 0;
 186 #define FLAG_INDEFINITE_LENGTH  0x01
 187 #define FLAG_MATCHED            0x02
 188 #define FLAG_LAST_MATCHED       0x04 /* Last tag matched */
 189 #define FLAG_CONS               0x20 /* Corresponds to CONS bit in the opcode tag
 190                                       * - ie. whether or not we are going to parse
 191                                       *   a compound type.
 192                                       */
 193
 194 #define NR_CONS_STACK 10
 195         unsigned short cons_dp_stack[NR_CONS_STACK];
 196         unsigned short cons_datalen_stack[NR_CONS_STACK];
 197         unsigned char cons_hdrlen_stack[NR_CONS_STACK];
 198 #define NR_JUMP_STACK 10
 199         unsigned char jump_stack[NR_JUMP_STACK];
 200
 201         if (datalen > 65535)
 202                 return -EMSGSIZE;
 203
 204 next_op:
 205         pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
 206                  pc, machlen, dp, datalen, csp, jsp);
 207         if (unlikely(pc >= machlen))
 208                 goto machine_overrun_error;
 209         op = machine[pc];
 210         if (unlikely(pc + asn1_op_lengths[op] > machlen))
 211                 goto machine_overrun_error;
 212
 213         /* If this command is meant to match a tag, then do that before
 214          * evaluating the command.
 215          */
 216         if (op <= ASN1_OP__MATCHES_TAG) {
 217                 unsigned char tmp;
 218
 219                 /* Skip conditional matches if possible */
 220                 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) ||
 221                     (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
 222                         flags &= ~FLAG_LAST_MATCHED;
 223                         pc += asn1_op_lengths[op];
 224                         goto next_op;
 225                 }
 226
 227                 flags = 0;
 228                 hdr = 2;
 229
 230                 /* Extract a tag from the data */
 231                 if (unlikely(datalen - dp < 2))
 232                         goto data_overrun_error;
 233                 tag = data[dp++];
 234                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
 235                         goto long_tag_not_supported;
 236
 237                 if (op & ASN1_OP_MATCH__ANY) {
 238                         pr_debug("- any %02x\n", tag);
 239                 } else {
 240                         /* Extract the tag from the machine
 241                          * - Either CONS or PRIM are permitted in the data if
 242                          *   CONS is not set in the op stream, otherwise CONS
 243                          *   is mandatory.
 244                          */
 245                         optag = machine[pc + 1];
 246                         flags |= optag & FLAG_CONS;
 247
 248                         /* Determine whether the tag matched */
 249                         tmp = optag ^ tag;
 250                         tmp &= ~(optag & ASN1_CONS_BIT);
 251                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
 252                         if (tmp != 0) {
 253                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
 254                                 if (op & ASN1_OP_MATCH__SKIP) {
 255                                         pc += asn1_op_lengths[op];
 256                                         dp--;
 257                                         goto next_op;
 258                                 }
 259                                 goto tag_mismatch;
 260                         }
 261                 }
 262                 flags |= FLAG_MATCHED;
 263
 264                 len = data[dp++];
 265                 if (len > 0x7f) {
 266                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 267                                 /* Indefinite length */
 268                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
 269                                         goto indefinite_len_primitive;
 270                                 flags |= FLAG_INDEFINITE_LENGTH;
 271                                 if (unlikely(2 > datalen - dp))
 272                                         goto data_overrun_error;
 273                         } else {
 274                                 int n = len - 0x80;
 275                                 if (unlikely(n > 2))
 276                                         goto length_too_long;
 277                                 if (unlikely(n > datalen - dp))
 278                                         goto data_overrun_error;
 279                                 hdr += n;
 280                                 for (len = 0; n > 0; n--) {
 281                                         len <<= 8;
 282                                         len |= data[dp++];
 283                                 }
 284                                 if (unlikely(len > datalen - dp))
 285                                         goto data_overrun_error;
 286                         }
 287                 } else {
 288                         if (unlikely(len > datalen - dp))
 289                                 goto data_overrun_error;
 290                 }
 291
 292                 if (flags & FLAG_CONS) {
 293                         /* For expected compound forms, we stack the positions
 294                          * of the start and end of the data.
 295                          */
 296                         if (unlikely(csp >= NR_CONS_STACK))
 297                                 goto cons_stack_overflow;
 298                         cons_dp_stack[csp] = dp;
 299                         cons_hdrlen_stack[csp] = hdr;
 300                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 301                                 cons_datalen_stack[csp] = datalen;
 302                                 datalen = dp + len;
 303                         } else {
 304                                 cons_datalen_stack[csp] = 0;
 305                         }
 306                         csp++;
 307                 }
 308
 309                 pr_debug("- TAG: %02x %zu%s\n",
 310                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 311                 tdp = dp;
 312         }
 313
 314         /* Decide how to handle the operation */
 315         switch (op) {
 316         case ASN1_OP_MATCH_ANY_ACT:
 317         case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
 318         case ASN1_OP_COND_MATCH_ANY_ACT:
 319         case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
 320                 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
 321                 if (ret < 0)
 322                         return ret;
 323                 goto skip_data;
 324
 325         case ASN1_OP_MATCH_ACT:
 326         case ASN1_OP_MATCH_ACT_OR_SKIP:
 327         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 328                 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
 329                 if (ret < 0)
 330                         return ret;
 331                 goto skip_data;
 332
 333         case ASN1_OP_MATCH:
 334         case ASN1_OP_MATCH_OR_SKIP:
 335         case ASN1_OP_MATCH_ANY:
 336         case ASN1_OP_MATCH_ANY_OR_SKIP:
 337         case ASN1_OP_COND_MATCH_OR_SKIP:
 338         case ASN1_OP_COND_MATCH_ANY:
 339         case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
 340         skip_data:
 341                 if (!(flags & FLAG_CONS)) {
 342                         if (flags & FLAG_INDEFINITE_LENGTH) {
 343                                 ret = asn1_find_indefinite_length(
 344                                         data, datalen, &dp, &len, &errmsg);
 345                                 if (ret < 0)
 346                                         goto error;
 347                         } else {
 348                                 dp += len;
 349                         }
 350                         pr_debug("- LEAF: %zu\n", len);
 351                 }
 352                 pc += asn1_op_lengths[op];
 353                 goto next_op;
 354
 355         case ASN1_OP_MATCH_JUMP:
 356         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 357         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 358                 pr_debug("- MATCH_JUMP\n");
 359                 if (unlikely(jsp == NR_JUMP_STACK))
 360                         goto jump_stack_overflow;
 361                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 362                 pc = machine[pc + 2];
 363                 goto next_op;
 364
 365         case ASN1_OP_COND_FAIL:
 366                 if (unlikely(!(flags & FLAG_MATCHED)))
 367                         goto tag_mismatch;
 368                 pc += asn1_op_lengths[op];
 369                 goto next_op;
 370
 371         case ASN1_OP_COMPLETE:
 372                 if (unlikely(jsp != 0 || csp != 0)) {
 373                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 374                                jsp, csp);
 375                         return -EBADMSG;
 376                 }
 377                 return 0;
 378
 379         case ASN1_OP_END_SET:
 380         case ASN1_OP_END_SET_ACT:
 381                 if (unlikely(!(flags & FLAG_MATCHED)))
 382                         goto tag_mismatch;
 383         case ASN1_OP_END_SEQ:
 384         case ASN1_OP_END_SET_OF:
 385         case ASN1_OP_END_SEQ_OF:
 386         case ASN1_OP_END_SEQ_ACT:
 387         case ASN1_OP_END_SET_OF_ACT:
 388         case ASN1_OP_END_SEQ_OF_ACT:
 389                 if (unlikely(csp <= 0))
 390                         goto cons_stack_underflow;
 391                 csp--;
 392                 tdp = cons_dp_stack[csp];
 393                 hdr = cons_hdrlen_stack[csp];
 394                 len = datalen;
 395                 datalen = cons_datalen_stack[csp];
 396                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 397                          tdp, dp, len, datalen);
 398                 if (datalen == 0) {
 399                         /* Indefinite length - check for the EOC. */
 400                         datalen = len;
 401                         if (unlikely(datalen - dp < 2))
 402                                 goto data_overrun_error;
 403                         if (data[dp++] != 0) {
 404                                 if (op & ASN1_OP_END__OF) {
 405                                         dp--;
 406                                         csp++;
 407                                         pc = machine[pc + 1];
 408                                         pr_debug("- continue\n");
 409                                         goto next_op;
 410                                 }
 411                                 goto missing_eoc;
 412                         }
 413                         if (data[dp++] != 0)
 414                                 goto invalid_eoc;
 415                         len = dp - tdp - 2;
 416                 } else {
 417                         if (dp < len && (op & ASN1_OP_END__OF)) {
 418                                 datalen = len;
 419                                 csp++;
 420                                 pc = machine[pc + 1];
 421                                 pr_debug("- continue\n");
 422                                 goto next_op;
 423                         }
 424                         if (dp != len)
 425                                 goto cons_length_error;
 426                         len -= tdp;
 427                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 428                 }
 429
 430                 if (op & ASN1_OP_END__ACT) {
 431                         unsigned char act;
 432                         if (op & ASN1_OP_END__OF)
 433                                 act = machine[pc + 2];
 434                         else
 435                                 act = machine[pc + 1];
 436                         ret = actions[act](context, hdr, 0, data + tdp, len);
 437                 }
 438                 pc += asn1_op_lengths[op];
 439                 goto next_op;
 440
 441         case ASN1_OP_MAYBE_ACT:
 442                 if (!(flags & FLAG_LAST_MATCHED)) {
 443                         pc += asn1_op_lengths[op];
 444                         goto next_op;
 445                 }
 446         case ASN1_OP_ACT:
 447                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 448                 if (ret < 0)
 449                         return ret;
 450                 pc += asn1_op_lengths[op];
 451                 goto next_op;
 452
 453         case ASN1_OP_RETURN:
 454                 if (unlikely(jsp <= 0))
 455                         goto jump_stack_underflow;
 456                 pc = jump_stack[--jsp];
 457                 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
 458                 goto next_op;
 459
 460         default:
 461                 break;
 462         }
 463
 464         /* Shouldn't reach here */
 465         pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n",
 466                op, pc);
 467         return -EBADMSG;
 468
 469 data_overrun_error:
 470         errmsg = "Data overrun error";
 471         goto error;
 472 machine_overrun_error:
 473         errmsg = "Machine overrun error";
 474         goto error;
 475 jump_stack_underflow:
 476         errmsg = "Jump stack underflow";
 477         goto error;
 478 jump_stack_overflow:
 479         errmsg = "Jump stack overflow";
 480         goto error;
 481 cons_stack_underflow:
 482         errmsg = "Cons stack underflow";
 483         goto error;
 484 cons_stack_overflow:
 485         errmsg = "Cons stack overflow";
 486         goto error;
 487 cons_length_error:
 488         errmsg = "Cons length error";
 489         goto error;
 490 missing_eoc:
 491         errmsg = "Missing EOC in indefinite len cons";
 492         goto error;
 493 invalid_eoc:
 494         errmsg = "Invalid length EOC";
 495         goto error;
 496 length_too_long:
 497         errmsg = "Unsupported length";
 498         goto error;
 499 indefinite_len_primitive:
 500         errmsg = "Indefinite len primitive not permitted";
 501         goto error;
 502 tag_mismatch:
 503         errmsg = "Unexpected tag";
 504         goto error;
 505 long_tag_not_supported:
 506         errmsg = "Long tag not supported";
 507 error:
 508         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 509                  errmsg, pc, dp, optag, tag, len);
 510         return -EBADMSG;
 511 }
 512 EXPORT_SYMBOL_GPL(asn1_ber_decoder);
 513
 514 MODULE_LICENSE("GPL");