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_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 == ASN1_EOC) {
  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                 goto check_length;
  96
  97         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
  98                 /* Indefinite length */
  99                 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
 100                         goto indefinite_len_primitive;
 101                 indef_level++;
 102                 goto next_tag;
 103         }
 104
 105         n = len - 0x80;
 106         if (unlikely(n > sizeof(len) - 1))
 107                 goto length_too_long;
 108         if (unlikely(n > datalen - dp))
 109                 goto data_overrun_error;
 110         len = 0;
 111         for (; n > 0; n--) {
 112                 len <<= 8;
 113                 len |= data[dp++];
 114         }
 115 check_length:
 116         if (len > datalen - dp)
 117                 goto data_overrun_error;
 118         dp += len;
 119         goto next_tag;
 120
 121 length_too_long:
 122         *_errmsg = "Unsupported length";
 123         goto error;
 124 indefinite_len_primitive:
 125         *_errmsg = "Indefinite len primitive not permitted";
 126         goto error;
 127 invalid_eoc:
 128         *_errmsg = "Invalid length EOC";
 129         goto error;
 130 data_overrun_error:
 131         *_errmsg = "Data overrun error";
 132         goto error;
 133 missing_eoc:
 134         *_errmsg = "Missing EOC in indefinite len cons";
 135 error:
 136         *_dp = dp;
 137         return -1;
 138 }
 139
 140 /**
 141  * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
 142  * @decoder: The decoder definition (produced by asn1_compiler)
 143  * @context: The caller's context (to be passed to the action functions)
 144  * @data: The encoded data
 145  * @datalen: The size of the encoded data
 146  *
 147  * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
 148  * produced by asn1_compiler.  Action functions are called on marked tags to
 149  * allow the caller to retrieve significant data.
 150  *
 151  * LIMITATIONS:
 152  *
 153  * To keep down the amount of stack used by this function, the following limits
 154  * have been imposed:
 155  *
 156  *  (1) This won't handle datalen > 65535 without increasing the size of the
 157  *      cons stack elements and length_too_long checking.
 158  *
 159  *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
 160  *      constructed types exceeds this, the decode will fail.
 161  *
 162  *  (3) The SET type (not the SET OF type) isn't really supported as tracking
 163  *      what members of the set have been seen is a pain.
 164  */
 165 int asn1_ber_decoder(const struct asn1_decoder *decoder,
 166                      void *context,
 167                      const unsigned char *data,
 168                      size_t datalen)
 169 {
 170         const unsigned char *machine = decoder->machine;
 171         const asn1_action_t *actions = decoder->actions;
 172         size_t machlen = decoder->machlen;
 173         enum asn1_opcode op;
 174         unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
 175         const char *errmsg;
 176         size_t pc = 0, dp = 0, tdp = 0, len = 0;
 177         int ret;
 178
 179         unsigned char flags = 0;
 180 #define FLAG_INDEFINITE_LENGTH  0x01
 181 #define FLAG_MATCHED            0x02
 182 #define FLAG_CONS               0x20 /* Corresponds to CONS bit in the opcode tag
 183                                       * - ie. whether or not we are going to parse
 184                                       *   a compound type.
 185                                       */
 186
 187 #define NR_CONS_STACK 10
 188         unsigned short cons_dp_stack[NR_CONS_STACK];
 189         unsigned short cons_datalen_stack[NR_CONS_STACK];
 190         unsigned char cons_hdrlen_stack[NR_CONS_STACK];
 191 #define NR_JUMP_STACK 10
 192         unsigned char jump_stack[NR_JUMP_STACK];
 193
 194         if (datalen > 65535)
 195                 return -EMSGSIZE;
 196
 197 next_op:
 198         pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
 199                  pc, machlen, dp, datalen, csp, jsp);
 200         if (unlikely(pc >= machlen))
 201                 goto machine_overrun_error;
 202         op = machine[pc];
 203         if (unlikely(pc + asn1_op_lengths[op] > machlen))
 204                 goto machine_overrun_error;
 205
 206         /* If this command is meant to match a tag, then do that before
 207          * evaluating the command.
 208          */
 209         if (op <= ASN1_OP__MATCHES_TAG) {
 210                 unsigned char tmp;
 211
 212                 /* Skip conditional matches if possible */
 213                 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) ||
 214                     (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
 215                         pc += asn1_op_lengths[op];
 216                         goto next_op;
 217                 }
 218
 219                 flags = 0;
 220                 hdr = 2;
 221
 222                 /* Extract a tag from the data */
 223                 if (unlikely(datalen - dp < 2))
 224                         goto data_overrun_error;
 225                 tag = data[dp++];
 226                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
 227                         goto long_tag_not_supported;
 228
 229                 if (op & ASN1_OP_MATCH__ANY) {
 230                         pr_debug("- any %02x\n", tag);
 231                 } else {
 232                         /* Extract the tag from the machine
 233                          * - Either CONS or PRIM are permitted in the data if
 234                          *   CONS is not set in the op stream, otherwise CONS
 235                          *   is mandatory.
 236                          */
 237                         optag = machine[pc + 1];
 238                         flags |= optag & FLAG_CONS;
 239
 240                         /* Determine whether the tag matched */
 241                         tmp = optag ^ tag;
 242                         tmp &= ~(optag & ASN1_CONS_BIT);
 243                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
 244                         if (tmp != 0) {
 245                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
 246                                 if (op & ASN1_OP_MATCH__SKIP) {
 247                                         pc += asn1_op_lengths[op];
 248                                         dp--;
 249                                         goto next_op;
 250                                 }
 251                                 goto tag_mismatch;
 252                         }
 253                 }
 254                 flags |= FLAG_MATCHED;
 255
 256                 len = data[dp++];
 257                 if (len > 0x7f) {
 258                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 259                                 /* Indefinite length */
 260                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
 261                                         goto indefinite_len_primitive;
 262                                 flags |= FLAG_INDEFINITE_LENGTH;
 263                                 if (unlikely(2 > datalen - dp))
 264                                         goto data_overrun_error;
 265                         } else {
 266                                 int n = len - 0x80;
 267                                 if (unlikely(n > 2))
 268                                         goto length_too_long;
 269                                 if (unlikely(n > datalen - dp))
 270                                         goto data_overrun_error;
 271                                 hdr += n;
 272                                 for (len = 0; n > 0; n--) {
 273                                         len <<= 8;
 274                                         len |= data[dp++];
 275                                 }
 276                                 if (unlikely(len > datalen - dp))
 277                                         goto data_overrun_error;
 278                         }
 279                 } else {
 280                         if (unlikely(len > datalen - dp))
 281                                 goto data_overrun_error;
 282                 }
 283
 284                 if (flags & FLAG_CONS) {
 285                         /* For expected compound forms, we stack the positions
 286                          * of the start and end of the data.
 287                          */
 288                         if (unlikely(csp >= NR_CONS_STACK))
 289                                 goto cons_stack_overflow;
 290                         cons_dp_stack[csp] = dp;
 291                         cons_hdrlen_stack[csp] = hdr;
 292                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 293                                 cons_datalen_stack[csp] = datalen;
 294                                 datalen = dp + len;
 295                         } else {
 296                                 cons_datalen_stack[csp] = 0;
 297                         }
 298                         csp++;
 299                 }
 300
 301                 pr_debug("- TAG: %02x %zu%s\n",
 302                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 303                 tdp = dp;
 304         }
 305
 306         /* Decide how to handle the operation */
 307         switch (op) {
 308         case ASN1_OP_MATCH:
 309         case ASN1_OP_MATCH_OR_SKIP:
 310         case ASN1_OP_MATCH_ACT:
 311         case ASN1_OP_MATCH_ACT_OR_SKIP:
 312         case ASN1_OP_MATCH_ANY:
 313         case ASN1_OP_MATCH_ANY_ACT:
 314         case ASN1_OP_COND_MATCH_OR_SKIP:
 315         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 316         case ASN1_OP_COND_MATCH_ANY:
 317         case ASN1_OP_COND_MATCH_ANY_ACT:
 318
 319                 if (!(flags & FLAG_CONS)) {
 320                         if (flags & FLAG_INDEFINITE_LENGTH) {
 321                                 size_t tmp = dp;
 322
 323                                 ret = asn1_find_indefinite_length(
 324                                         data, datalen, &tmp, &len, &errmsg);
 325                                 if (ret < 0)
 326                                         goto error;
 327                         }
 328                         pr_debug("- LEAF: %zu\n", len);
 329                 }
 330
 331                 if (op & ASN1_OP_MATCH__ACT) {
 332                         unsigned char act;
 333
 334                         if (op & ASN1_OP_MATCH__ANY)
 335                                 act = machine[pc + 1];
 336                         else
 337                                 act = machine[pc + 2];
 338                         ret = actions[act](context, hdr, tag, data + dp, len);
 339                         if (ret < 0)
 340                                 return ret;
 341                 }
 342
 343                 if (!(flags & FLAG_CONS))
 344                         dp += len;
 345                 pc += asn1_op_lengths[op];
 346                 goto next_op;
 347
 348         case ASN1_OP_MATCH_JUMP:
 349         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 350         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 351                 pr_debug("- MATCH_JUMP\n");
 352                 if (unlikely(jsp == NR_JUMP_STACK))
 353                         goto jump_stack_overflow;
 354                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 355                 pc = machine[pc + 2];
 356                 goto next_op;
 357
 358         case ASN1_OP_COND_FAIL:
 359                 if (unlikely(!(flags & FLAG_MATCHED)))
 360                         goto tag_mismatch;
 361                 pc += asn1_op_lengths[op];
 362                 goto next_op;
 363
 364         case ASN1_OP_COMPLETE:
 365                 if (unlikely(jsp != 0 || csp != 0)) {
 366                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 367                                jsp, csp);
 368                         return -EBADMSG;
 369                 }
 370                 return 0;
 371
 372         case ASN1_OP_END_SET:
 373         case ASN1_OP_END_SET_ACT:
 374                 if (unlikely(!(flags & FLAG_MATCHED)))
 375                         goto tag_mismatch;
 376         case ASN1_OP_END_SEQ:
 377         case ASN1_OP_END_SET_OF:
 378         case ASN1_OP_END_SEQ_OF:
 379         case ASN1_OP_END_SEQ_ACT:
 380         case ASN1_OP_END_SET_OF_ACT:
 381         case ASN1_OP_END_SEQ_OF_ACT:
 382                 if (unlikely(csp <= 0))
 383                         goto cons_stack_underflow;
 384                 csp--;
 385                 tdp = cons_dp_stack[csp];
 386                 hdr = cons_hdrlen_stack[csp];
 387                 len = datalen;
 388                 datalen = cons_datalen_stack[csp];
 389                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 390                          tdp, dp, len, datalen);
 391                 if (datalen == 0) {
 392                         /* Indefinite length - check for the EOC. */
 393                         datalen = len;
 394                         if (unlikely(datalen - dp < 2))
 395                                 goto data_overrun_error;
 396                         if (data[dp++] != 0) {
 397                                 if (op & ASN1_OP_END__OF) {
 398                                         dp--;
 399                                         csp++;
 400                                         pc = machine[pc + 1];
 401                                         pr_debug("- continue\n");
 402                                         goto next_op;
 403                                 }
 404                                 goto missing_eoc;
 405                         }
 406                         if (data[dp++] != 0)
 407                                 goto invalid_eoc;
 408                         len = dp - tdp - 2;
 409                 } else {
 410                         if (dp < len && (op & ASN1_OP_END__OF)) {
 411                                 datalen = len;
 412                                 csp++;
 413                                 pc = machine[pc + 1];
 414                                 pr_debug("- continue\n");
 415                                 goto next_op;
 416                         }
 417                         if (dp != len)
 418                                 goto cons_length_error;
 419                         len -= tdp;
 420                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 421                 }
 422
 423                 if (op & ASN1_OP_END__ACT) {
 424                         unsigned char act;
 425                         if (op & ASN1_OP_END__OF)
 426                                 act = machine[pc + 2];
 427                         else
 428                                 act = machine[pc + 1];
 429                         ret = actions[act](context, hdr, 0, data + tdp, len);
 430                         if (ret < 0)
 431                                 return ret;
 432                 }
 433                 pc += asn1_op_lengths[op];
 434                 goto next_op;
 435
 436         case ASN1_OP_ACT:
 437                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 438                 pc += asn1_op_lengths[op];
 439                 goto next_op;
 440
 441         case ASN1_OP_RETURN:
 442                 if (unlikely(jsp <= 0))
 443                         goto jump_stack_underflow;
 444                 pc = jump_stack[--jsp];
 445                 goto next_op;
 446
 447         default:
 448                 break;
 449         }
 450
 451         /* Shouldn't reach here */
 452         pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op);
 453         return -EBADMSG;
 454
 455 data_overrun_error:
 456         errmsg = "Data overrun error";
 457         goto error;
 458 machine_overrun_error:
 459         errmsg = "Machine overrun error";
 460         goto error;
 461 jump_stack_underflow:
 462         errmsg = "Jump stack underflow";
 463         goto error;
 464 jump_stack_overflow:
 465         errmsg = "Jump stack overflow";
 466         goto error;
 467 cons_stack_underflow:
 468         errmsg = "Cons stack underflow";
 469         goto error;
 470 cons_stack_overflow:
 471         errmsg = "Cons stack overflow";
 472         goto error;
 473 cons_length_error:
 474         errmsg = "Cons length error";
 475         goto error;
 476 missing_eoc:
 477         errmsg = "Missing EOC in indefinite len cons";
 478         goto error;
 479 invalid_eoc:
 480         errmsg = "Invalid length EOC";
 481         goto error;
 482 length_too_long:
 483         errmsg = "Unsupported length";
 484         goto error;
 485 indefinite_len_primitive:
 486         errmsg = "Indefinite len primitive not permitted";
 487         goto error;
 488 tag_mismatch:
 489         errmsg = "Unexpected tag";
 490         goto error;
 491 long_tag_not_supported:
 492         errmsg = "Long tag not supported";
 493 error:
 494         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 495                  errmsg, pc, dp, optag, tag, len);
 496         return -EBADMSG;
 497 }
 498 EXPORT_SYMBOL_GPL(asn1_ber_decoder);