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(dp >= datalen - 1))
 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(dp >= datalen - n))
 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                 }
 280
 281                 if (flags & FLAG_CONS) {
 282                         /* For expected compound forms, we stack the positions
 283                          * of the start and end of the data.
 284                          */
 285                         if (unlikely(csp >= NR_CONS_STACK))
 286                                 goto cons_stack_overflow;
 287                         cons_dp_stack[csp] = dp;
 288                         cons_hdrlen_stack[csp] = hdr;
 289                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 290                                 cons_datalen_stack[csp] = datalen;
 291                                 datalen = dp + len;
 292                         } else {
 293                                 cons_datalen_stack[csp] = 0;
 294                         }
 295                         csp++;
 296                 }
 297
 298                 pr_debug("- TAG: %02x %zu%s\n",
 299                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 300                 tdp = dp;
 301         }
 302
 303         /* Decide how to handle the operation */
 304         switch (op) {
 305         case ASN1_OP_MATCH_ANY_ACT:
 306         case ASN1_OP_COND_MATCH_ANY_ACT:
 307                 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
 308                 if (ret < 0)
 309                         return ret;
 310                 goto skip_data;
 311
 312         case ASN1_OP_MATCH_ACT:
 313         case ASN1_OP_MATCH_ACT_OR_SKIP:
 314         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 315                 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
 316                 if (ret < 0)
 317                         return ret;
 318                 goto skip_data;
 319
 320         case ASN1_OP_MATCH:
 321         case ASN1_OP_MATCH_OR_SKIP:
 322         case ASN1_OP_MATCH_ANY:
 323         case ASN1_OP_COND_MATCH_OR_SKIP:
 324         case ASN1_OP_COND_MATCH_ANY:
 325         skip_data:
 326                 if (!(flags & FLAG_CONS)) {
 327                         if (flags & FLAG_INDEFINITE_LENGTH) {
 328                                 ret = asn1_find_indefinite_length(
 329                                         data, datalen, &dp, &len, &errmsg);
 330                                 if (ret < 0)
 331                                         goto error;
 332                         } else {
 333                                 dp += len;
 334                         }
 335                         pr_debug("- LEAF: %zu\n", len);
 336                 }
 337                 pc += asn1_op_lengths[op];
 338                 goto next_op;
 339
 340         case ASN1_OP_MATCH_JUMP:
 341         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 342         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 343                 pr_debug("- MATCH_JUMP\n");
 344                 if (unlikely(jsp == NR_JUMP_STACK))
 345                         goto jump_stack_overflow;
 346                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 347                 pc = machine[pc + 2];
 348                 goto next_op;
 349
 350         case ASN1_OP_COND_FAIL:
 351                 if (unlikely(!(flags & FLAG_MATCHED)))
 352                         goto tag_mismatch;
 353                 pc += asn1_op_lengths[op];
 354                 goto next_op;
 355
 356         case ASN1_OP_COMPLETE:
 357                 if (unlikely(jsp != 0 || csp != 0)) {
 358                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 359                                jsp, csp);
 360                         return -EBADMSG;
 361                 }
 362                 return 0;
 363
 364         case ASN1_OP_END_SET:
 365         case ASN1_OP_END_SET_ACT:
 366                 if (unlikely(!(flags & FLAG_MATCHED)))
 367                         goto tag_mismatch;
 368         case ASN1_OP_END_SEQ:
 369         case ASN1_OP_END_SET_OF:
 370         case ASN1_OP_END_SEQ_OF:
 371         case ASN1_OP_END_SEQ_ACT:
 372         case ASN1_OP_END_SET_OF_ACT:
 373         case ASN1_OP_END_SEQ_OF_ACT:
 374                 if (unlikely(csp <= 0))
 375                         goto cons_stack_underflow;
 376                 csp--;
 377                 tdp = cons_dp_stack[csp];
 378                 hdr = cons_hdrlen_stack[csp];
 379                 len = datalen;
 380                 datalen = cons_datalen_stack[csp];
 381                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 382                          tdp, dp, len, datalen);
 383                 if (datalen == 0) {
 384                         /* Indefinite length - check for the EOC. */
 385                         datalen = len;
 386                         if (unlikely(datalen - dp < 2))
 387                                 goto data_overrun_error;
 388                         if (data[dp++] != 0) {
 389                                 if (op & ASN1_OP_END__OF) {
 390                                         dp--;
 391                                         csp++;
 392                                         pc = machine[pc + 1];
 393                                         pr_debug("- continue\n");
 394                                         goto next_op;
 395                                 }
 396                                 goto missing_eoc;
 397                         }
 398                         if (data[dp++] != 0)
 399                                 goto invalid_eoc;
 400                         len = dp - tdp - 2;
 401                 } else {
 402                         if (dp < len && (op & ASN1_OP_END__OF)) {
 403                                 datalen = len;
 404                                 csp++;
 405                                 pc = machine[pc + 1];
 406                                 pr_debug("- continue\n");
 407                                 goto next_op;
 408                         }
 409                         if (dp != len)
 410                                 goto cons_length_error;
 411                         len -= tdp;
 412                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 413                 }
 414
 415                 if (op & ASN1_OP_END__ACT) {
 416                         unsigned char act;
 417                         if (op & ASN1_OP_END__OF)
 418                                 act = machine[pc + 2];
 419                         else
 420                                 act = machine[pc + 1];
 421                         ret = actions[act](context, hdr, 0, data + tdp, len);
 422                 }
 423                 pc += asn1_op_lengths[op];
 424                 goto next_op;
 425
 426         case ASN1_OP_ACT:
 427                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 428                 pc += asn1_op_lengths[op];
 429                 goto next_op;
 430
 431         case ASN1_OP_RETURN:
 432                 if (unlikely(jsp <= 0))
 433                         goto jump_stack_underflow;
 434                 pc = jump_stack[--jsp];
 435                 goto next_op;
 436
 437         default:
 438                 break;
 439         }
 440
 441         /* Shouldn't reach here */
 442         pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op);
 443         return -EBADMSG;
 444
 445 data_overrun_error:
 446         errmsg = "Data overrun error";
 447         goto error;
 448 machine_overrun_error:
 449         errmsg = "Machine overrun error";
 450         goto error;
 451 jump_stack_underflow:
 452         errmsg = "Jump stack underflow";
 453         goto error;
 454 jump_stack_overflow:
 455         errmsg = "Jump stack overflow";
 456         goto error;
 457 cons_stack_underflow:
 458         errmsg = "Cons stack underflow";
 459         goto error;
 460 cons_stack_overflow:
 461         errmsg = "Cons stack overflow";
 462         goto error;
 463 cons_length_error:
 464         errmsg = "Cons length error";
 465         goto error;
 466 missing_eoc:
 467         errmsg = "Missing EOC in indefinite len cons";
 468         goto error;
 469 invalid_eoc:
 470         errmsg = "Invalid length EOC";
 471         goto error;
 472 length_too_long:
 473         errmsg = "Unsupported length";
 474         goto error;
 475 indefinite_len_primitive:
 476         errmsg = "Indefinite len primitive not permitted";
 477         goto error;
 478 tag_mismatch:
 479         errmsg = "Unexpected tag";
 480         goto error;
 481 long_tag_not_supported:
 482         errmsg = "Long tag not supported";
 483 error:
 484         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 485                  errmsg, pc, dp, optag, tag, len);
 486         return -EBADMSG;
 487 }
 488 EXPORT_SYMBOL_GPL(asn1_ber_decoder);