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/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(datalen - dp < 2))
 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(n > datalen - dp))
 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                 } else {
 287                         if (unlikely(len > datalen - dp))
 288                                 goto data_overrun_error;
 289                 }
 290
 291                 if (flags & FLAG_CONS) {
 292                         /* For expected compound forms, we stack the positions
 293                          * of the start and end of the data.
 294                          */
 295                         if (unlikely(csp >= NR_CONS_STACK))
 296                                 goto cons_stack_overflow;
 297                         cons_dp_stack[csp] = dp;
 298                         cons_hdrlen_stack[csp] = hdr;
 299                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 300                                 cons_datalen_stack[csp] = datalen;
 301                                 datalen = dp + len;
 302                         } else {
 303                                 cons_datalen_stack[csp] = 0;
 304                         }
 305                         csp++;
 306                 }
 307
 308                 pr_debug("- TAG: %02x %zu%s\n",
 309                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 310                 tdp = dp;
 311         }
 312
 313         /* Decide how to handle the operation */
 314         switch (op) {
 315         case ASN1_OP_MATCH:
 316         case ASN1_OP_MATCH_OR_SKIP:
 317         case ASN1_OP_MATCH_ACT:
 318         case ASN1_OP_MATCH_ACT_OR_SKIP:
 319         case ASN1_OP_MATCH_ANY:
 320         case ASN1_OP_MATCH_ANY_OR_SKIP:
 321         case ASN1_OP_MATCH_ANY_ACT:
 322         case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
 323         case ASN1_OP_COND_MATCH_OR_SKIP:
 324         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 325         case ASN1_OP_COND_MATCH_ANY:
 326         case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
 327         case ASN1_OP_COND_MATCH_ANY_ACT:
 328         case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
 329
 330                 if (!(flags & FLAG_CONS)) {
 331                         if (flags & FLAG_INDEFINITE_LENGTH) {
 332                                 size_t tmp = dp;
 333
 334                                 ret = asn1_find_indefinite_length(
 335                                         data, datalen, &tmp, &len, &errmsg);
 336                                 if (ret < 0)
 337                                         goto error;
 338                         }
 339                         pr_debug("- LEAF: %zu\n", len);
 340                 }
 341
 342                 if (op & ASN1_OP_MATCH__ACT) {
 343                         unsigned char act;
 344
 345                         if (op & ASN1_OP_MATCH__ANY)
 346                                 act = machine[pc + 1];
 347                         else
 348                                 act = machine[pc + 2];
 349                         ret = actions[act](context, hdr, tag, data + dp, len);
 350                         if (ret < 0)
 351                                 return ret;
 352                 }
 353
 354                 if (!(flags & FLAG_CONS))
 355                         dp += len;
 356                 pc += asn1_op_lengths[op];
 357                 goto next_op;
 358
 359         case ASN1_OP_MATCH_JUMP:
 360         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 361         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 362                 pr_debug("- MATCH_JUMP\n");
 363                 if (unlikely(jsp == NR_JUMP_STACK))
 364                         goto jump_stack_overflow;
 365                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 366                 pc = machine[pc + 2];
 367                 goto next_op;
 368
 369         case ASN1_OP_COND_FAIL:
 370                 if (unlikely(!(flags & FLAG_MATCHED)))
 371                         goto tag_mismatch;
 372                 pc += asn1_op_lengths[op];
 373                 goto next_op;
 374
 375         case ASN1_OP_COMPLETE:
 376                 if (unlikely(jsp != 0 || csp != 0)) {
 377                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 378                                jsp, csp);
 379                         return -EBADMSG;
 380                 }
 381                 return 0;
 382
 383         case ASN1_OP_END_SET:
 384         case ASN1_OP_END_SET_ACT:
 385                 if (unlikely(!(flags & FLAG_MATCHED)))
 386                         goto tag_mismatch;
 387         case ASN1_OP_END_SEQ:
 388         case ASN1_OP_END_SET_OF:
 389         case ASN1_OP_END_SEQ_OF:
 390         case ASN1_OP_END_SEQ_ACT:
 391         case ASN1_OP_END_SET_OF_ACT:
 392         case ASN1_OP_END_SEQ_OF_ACT:
 393                 if (unlikely(csp <= 0))
 394                         goto cons_stack_underflow;
 395                 csp--;
 396                 tdp = cons_dp_stack[csp];
 397                 hdr = cons_hdrlen_stack[csp];
 398                 len = datalen;
 399                 datalen = cons_datalen_stack[csp];
 400                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 401                          tdp, dp, len, datalen);
 402                 if (datalen == 0) {
 403                         /* Indefinite length - check for the EOC. */
 404                         datalen = len;
 405                         if (unlikely(datalen - dp < 2))
 406                                 goto data_overrun_error;
 407                         if (data[dp++] != 0) {
 408                                 if (op & ASN1_OP_END__OF) {
 409                                         dp--;
 410                                         csp++;
 411                                         pc = machine[pc + 1];
 412                                         pr_debug("- continue\n");
 413                                         goto next_op;
 414                                 }
 415                                 goto missing_eoc;
 416                         }
 417                         if (data[dp++] != 0)
 418                                 goto invalid_eoc;
 419                         len = dp - tdp - 2;
 420                 } else {
 421                         if (dp < len && (op & ASN1_OP_END__OF)) {
 422                                 datalen = len;
 423                                 csp++;
 424                                 pc = machine[pc + 1];
 425                                 pr_debug("- continue\n");
 426                                 goto next_op;
 427                         }
 428                         if (dp != len)
 429                                 goto cons_length_error;
 430                         len -= tdp;
 431                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 432                 }
 433
 434                 if (op & ASN1_OP_END__ACT) {
 435                         unsigned char act;
 436                         if (op & ASN1_OP_END__OF)
 437                                 act = machine[pc + 2];
 438                         else
 439                                 act = machine[pc + 1];
 440                         ret = actions[act](context, hdr, 0, data + tdp, len);
 441                         if (ret < 0)
 442                                 return ret;
 443                 }
 444                 pc += asn1_op_lengths[op];
 445                 goto next_op;
 446
 447         case ASN1_OP_MAYBE_ACT:
 448                 if (!(flags & FLAG_LAST_MATCHED)) {
 449                         pc += asn1_op_lengths[op];
 450                         goto next_op;
 451                 }
 452         case ASN1_OP_ACT:
 453                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 454                 if (ret < 0)
 455                         return ret;
 456                 pc += asn1_op_lengths[op];
 457                 goto next_op;
 458
 459         case ASN1_OP_RETURN:
 460                 if (unlikely(jsp <= 0))
 461                         goto jump_stack_underflow;
 462                 pc = jump_stack[--jsp];
 463                 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
 464                 goto next_op;
 465
 466         default:
 467                 break;
 468         }
 469
 470         /* Shouldn't reach here */
 471         pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n",
 472                op, pc);
 473         return -EBADMSG;
 474
 475 data_overrun_error:
 476         errmsg = "Data overrun error";
 477         goto error;
 478 machine_overrun_error:
 479         errmsg = "Machine overrun error";
 480         goto error;
 481 jump_stack_underflow:
 482         errmsg = "Jump stack underflow";
 483         goto error;
 484 jump_stack_overflow:
 485         errmsg = "Jump stack overflow";
 486         goto error;
 487 cons_stack_underflow:
 488         errmsg = "Cons stack underflow";
 489         goto error;
 490 cons_stack_overflow:
 491         errmsg = "Cons stack overflow";
 492         goto error;
 493 cons_length_error:
 494         errmsg = "Cons length error";
 495         goto error;
 496 missing_eoc:
 497         errmsg = "Missing EOC in indefinite len cons";
 498         goto error;
 499 invalid_eoc:
 500         errmsg = "Invalid length EOC";
 501         goto error;
 502 length_too_long:
 503         errmsg = "Unsupported length";
 504         goto error;
 505 indefinite_len_primitive:
 506         errmsg = "Indefinite len primitive not permitted";
 507         goto error;
 508 tag_mismatch:
 509         errmsg = "Unexpected tag";
 510         goto error;
 511 long_tag_not_supported:
 512         errmsg = "Long tag not supported";
 513 error:
 514         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 515                  errmsg, pc, dp, optag, tag, len);
 516         return -EBADMSG;
 517 }
 518 EXPORT_SYMBOL_GPL(asn1_ber_decoder);