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