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