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