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  * @datasize: 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 &&
 212                      flags & FLAG_MATCHED) ||
 213                     dp == datalen) {
 214                         pc += asn1_op_lengths[op];
 215                         goto next_op;
 216                 }
 217
 218                 flags = 0;
 219                 hdr = 2;
 220
 221                 /* Extract a tag from the data */
 222                 if (unlikely(dp >= datalen - 1))
 223                         goto data_overrun_error;
 224                 tag = data[dp++];
 225                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
 226                         goto long_tag_not_supported;
 227
 228                 if (op & ASN1_OP_MATCH__ANY) {
 229                         pr_debug("- any %02x\n", tag);
 230                 } else {
 231                         /* Extract the tag from the machine
 232                          * - Either CONS or PRIM are permitted in the data if
 233                          *   CONS is not set in the op stream, otherwise CONS
 234                          *   is mandatory.
 235                          */
 236                         optag = machine[pc + 1];
 237                         flags |= optag & FLAG_CONS;
 238
 239                         /* Determine whether the tag matched */
 240                         tmp = optag ^ tag;
 241                         tmp &= ~(optag & ASN1_CONS_BIT);
 242                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
 243                         if (tmp != 0) {
 244                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
 245                                 if (op & ASN1_OP_MATCH__SKIP) {
 246                                         pc += asn1_op_lengths[op];
 247                                         dp--;
 248                                         goto next_op;
 249                                 }
 250                                 goto tag_mismatch;
 251                         }
 252                 }
 253                 flags |= FLAG_MATCHED;
 254
 255                 len = data[dp++];
 256                 if (len > 0x7f) {
 257                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 258                                 /* Indefinite length */
 259                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
 260                                         goto indefinite_len_primitive;
 261                                 flags |= FLAG_INDEFINITE_LENGTH;
 262                                 if (unlikely(2 > datalen - dp))
 263                                         goto data_overrun_error;
 264                         } else {
 265                                 int n = len - 0x80;
 266                                 if (unlikely(n > 2))
 267                                         goto length_too_long;
 268                                 if (unlikely(dp >= datalen - n))
 269                                         goto data_overrun_error;
 270                                 hdr += n;
 271                                 for (len = 0; n > 0; n--) {
 272                                         len <<= 8;
 273                                         len |= data[dp++];
 274                                 }
 275                                 if (unlikely(len > datalen - dp))
 276                                         goto data_overrun_error;
 277                         }
 278                 }
 279
 280                 if (flags & FLAG_CONS) {
 281                         /* For expected compound forms, we stack the positions
 282                          * of the start and end of the data.
 283                          */
 284                         if (unlikely(csp >= NR_CONS_STACK))
 285                                 goto cons_stack_overflow;
 286                         cons_dp_stack[csp] = dp;
 287                         cons_hdrlen_stack[csp] = hdr;
 288                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 289                                 cons_datalen_stack[csp] = datalen;
 290                                 datalen = dp + len;
 291                         } else {
 292                                 cons_datalen_stack[csp] = 0;
 293                         }
 294                         csp++;
 295                 }
 296
 297                 pr_debug("- TAG: %02x %zu%s\n",
 298                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 299                 tdp = dp;
 300         }
 301
 302         /* Decide how to handle the operation */
 303         switch (op) {
 304         case ASN1_OP_MATCH_ANY_ACT:
 305         case ASN1_OP_COND_MATCH_ANY_ACT:
 306                 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
 307                 if (ret < 0)
 308                         return ret;
 309                 goto skip_data;
 310
 311         case ASN1_OP_MATCH_ACT:
 312         case ASN1_OP_MATCH_ACT_OR_SKIP:
 313         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 314                 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
 315                 if (ret < 0)
 316                         return ret;
 317                 goto skip_data;
 318
 319         case ASN1_OP_MATCH:
 320         case ASN1_OP_MATCH_OR_SKIP:
 321         case ASN1_OP_MATCH_ANY:
 322         case ASN1_OP_COND_MATCH_OR_SKIP:
 323         case ASN1_OP_COND_MATCH_ANY:
 324         skip_data:
 325                 if (!(flags & FLAG_CONS)) {
 326                         if (flags & FLAG_INDEFINITE_LENGTH) {
 327                                 ret = asn1_find_indefinite_length(
 328                                         data, datalen, &dp, &len, &errmsg);
 329                                 if (ret < 0)
 330                                         goto error;
 331                         } else {
 332                                 dp += len;
 333                         }
 334                         pr_debug("- LEAF: %zu\n", len);
 335                 }
 336                 pc += asn1_op_lengths[op];
 337                 goto next_op;
 338
 339         case ASN1_OP_MATCH_JUMP:
 340         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 341         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 342                 pr_debug("- MATCH_JUMP\n");
 343                 if (unlikely(jsp == NR_JUMP_STACK))
 344                         goto jump_stack_overflow;
 345                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 346                 pc = machine[pc + 2];
 347                 goto next_op;
 348
 349         case ASN1_OP_COND_FAIL:
 350                 if (unlikely(!(flags & FLAG_MATCHED)))
 351                         goto tag_mismatch;
 352                 pc += asn1_op_lengths[op];
 353                 goto next_op;
 354
 355         case ASN1_OP_COMPLETE:
 356                 if (unlikely(jsp != 0 || csp != 0)) {
 357                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 358                                jsp, csp);
 359                         return -EBADMSG;
 360                 }
 361                 return 0;
 362
 363         case ASN1_OP_END_SET:
 364         case ASN1_OP_END_SET_ACT:
 365                 if (unlikely(!(flags & FLAG_MATCHED)))
 366                         goto tag_mismatch;
 367         case ASN1_OP_END_SEQ:
 368         case ASN1_OP_END_SET_OF:
 369         case ASN1_OP_END_SEQ_OF:
 370         case ASN1_OP_END_SEQ_ACT:
 371         case ASN1_OP_END_SET_OF_ACT:
 372         case ASN1_OP_END_SEQ_OF_ACT:
 373                 if (unlikely(csp <= 0))
 374                         goto cons_stack_underflow;
 375                 csp--;
 376                 tdp = cons_dp_stack[csp];
 377                 hdr = cons_hdrlen_stack[csp];
 378                 len = datalen;
 379                 datalen = cons_datalen_stack[csp];
 380                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 381                          tdp, dp, len, datalen);
 382                 if (datalen == 0) {
 383                         /* Indefinite length - check for the EOC. */
 384                         datalen = len;
 385                         if (unlikely(datalen - dp < 2))
 386                                 goto data_overrun_error;
 387                         if (data[dp++] != 0) {
 388                                 if (op & ASN1_OP_END__OF) {
 389                                         dp--;
 390                                         csp++;
 391                                         pc = machine[pc + 1];
 392                                         pr_debug("- continue\n");
 393                                         goto next_op;
 394                                 }
 395                                 goto missing_eoc;
 396                         }
 397                         if (data[dp++] != 0)
 398                                 goto invalid_eoc;
 399                         len = dp - tdp - 2;
 400                 } else {
 401                         if (dp < len && (op & ASN1_OP_END__OF)) {
 402                                 datalen = len;
 403                                 csp++;
 404                                 pc = machine[pc + 1];
 405                                 pr_debug("- continue\n");
 406                                 goto next_op;
 407                         }
 408                         if (dp != len)
 409                                 goto cons_length_error;
 410                         len -= tdp;
 411                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 412                 }
 413
 414                 if (op & ASN1_OP_END__ACT) {
 415                         unsigned char act;
 416                         if (op & ASN1_OP_END__OF)
 417                                 act = machine[pc + 2];
 418                         else
 419                                 act = machine[pc + 1];
 420                         ret = actions[act](context, hdr, 0, data + tdp, len);
 421                 }
 422                 pc += asn1_op_lengths[op];
 423                 goto next_op;
 424
 425         case ASN1_OP_ACT:
 426                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 427                 pc += asn1_op_lengths[op];
 428                 goto next_op;
 429
 430         case ASN1_OP_RETURN:
 431                 if (unlikely(jsp <= 0))
 432                         goto jump_stack_underflow;
 433                 pc = jump_stack[--jsp];
 434                 goto next_op;
 435
 436         default:
 437                 break;
 438         }
 439
 440         /* Shouldn't reach here */
 441         pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op);
 442         return -EBADMSG;
 443
 444 data_overrun_error:
 445         errmsg = "Data overrun error";
 446         goto error;
 447 machine_overrun_error:
 448         errmsg = "Machine overrun error";
 449         goto error;
 450 jump_stack_underflow:
 451         errmsg = "Jump stack underflow";
 452         goto error;
 453 jump_stack_overflow:
 454         errmsg = "Jump stack overflow";
 455         goto error;
 456 cons_stack_underflow:
 457         errmsg = "Cons stack underflow";
 458         goto error;
 459 cons_stack_overflow:
 460         errmsg = "Cons stack overflow";
 461         goto error;
 462 cons_length_error:
 463         errmsg = "Cons length error";
 464         goto error;
 465 missing_eoc:
 466         errmsg = "Missing EOC in indefinite len cons";
 467         goto error;
 468 invalid_eoc:
 469         errmsg = "Invalid length EOC";
 470         goto error;
 471 length_too_long:
 472         errmsg = "Unsupported length";
 473         goto error;
 474 indefinite_len_primitive:
 475         errmsg = "Indefinite len primitive not permitted";
 476         goto error;
 477 tag_mismatch:
 478         errmsg = "Unexpected tag";
 479         goto error;
 480 long_tag_not_supported:
 481         errmsg = "Long tag not supported";
 482 error:
 483         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 484                  errmsg, pc, dp, optag, tag, len);
 485         return -EBADMSG;
 486 }
 487 EXPORT_SYMBOL_GPL(asn1_ber_decoder);