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_MAYBE_ACT]                     = 1         + 1,
  37         [ASN1_OP_RETURN]                        = 1,
  38         [ASN1_OP_END_SEQ]                       = 1,
  39         [ASN1_OP_END_SEQ_OF]                    = 1     + 1,
  40         [ASN1_OP_END_SET]                       = 1,
  41         [ASN1_OP_END_SET_OF]                    = 1     + 1,
  42         [ASN1_OP_END_SEQ_ACT]                   = 1         + 1,
  43         [ASN1_OP_END_SEQ_OF_ACT]                = 1     + 1 + 1,
  44         [ASN1_OP_END_SET_ACT]                   = 1         + 1,
  45         [ASN1_OP_END_SET_OF_ACT]                = 1     + 1 + 1,
  46 };
  47
  48 /*
  49  * Find the length of an indefinite length object
  50  * @data: The data buffer
  51  * @datalen: The end of the innermost containing element in the buffer
  52  * @_dp: The data parse cursor (updated before returning)
  53  * @_len: Where to return the size of the element.
  54  * @_errmsg: Where to return a pointer to an error message on error
  55  */
  56 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
  57                                        size_t *_dp, size_t *_len,
  58                                        const char **_errmsg)
  59 {
  60         unsigned char tag, tmp;
  61         size_t dp = *_dp, len, n;
  62         int indef_level = 1;
  63
  64 next_tag:
  65         if (unlikely(datalen - dp < 2)) {
  66                 if (datalen == dp)
  67                         goto missing_eoc;
  68                 goto data_overrun_error;
  69         }
  70
  71         /* Extract a tag from the data */
  72         tag = data[dp++];
  73         if (tag == 0) {
  74                 /* It appears to be an EOC. */
  75                 if (data[dp++] != 0)
  76                         goto invalid_eoc;
  77                 if (--indef_level <= 0) {
  78                         *_len = dp - *_dp;
  79                         *_dp = dp;
  80                         return 0;
  81                 }
  82                 goto next_tag;
  83         }
  84
  85         if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
  86                 do {
  87                         if (unlikely(datalen - dp < 2))
  88                                 goto data_overrun_error;
  89                         tmp = data[dp++];
  90                 } while (tmp & 0x80);
  91         }
  92
  93         /* Extract the length */
  94         len = data[dp++];
  95         if (len <= 0x7f) {
  96                 dp += len;
  97                 goto next_tag;
  98         }
  99
 100         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 101                 /* Indefinite length */
 102                 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
 103                         goto indefinite_len_primitive;
 104                 indef_level++;
 105                 goto next_tag;
 106         }
 107
 108         n = len - 0x80;
 109         if (unlikely(n > sizeof(size_t) - 1))
 110                 goto length_too_long;
 111         if (unlikely(n > datalen - dp))
 112                 goto data_overrun_error;
 113         for (len = 0; n > 0; n--) {
 114                 len <<= 8;
 115                 len |= data[dp++];
 116         }
 117         dp += len;
 118         goto next_tag;
 119
 120 length_too_long:
 121         *_errmsg = "Unsupported length";
 122         goto error;
 123 indefinite_len_primitive:
 124         *_errmsg = "Indefinite len primitive not permitted";
 125         goto error;
 126 invalid_eoc:
 127         *_errmsg = "Invalid length EOC";
 128         goto error;
 129 data_overrun_error:
 130         *_errmsg = "Data overrun error";
 131         goto error;
 132 missing_eoc:
 133         *_errmsg = "Missing EOC in indefinite len cons";
 134 error:
 135         *_dp = dp;
 136         return -1;
 137 }
 138
 139 /**
 140  * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
 141  * @decoder: The decoder definition (produced by asn1_compiler)
 142  * @context: The caller's context (to be passed to the action functions)
 143  * @data: The encoded data
 144  * @datalen: The size of the encoded data
 145  *
 146  * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
 147  * produced by asn1_compiler.  Action functions are called on marked tags to
 148  * allow the caller to retrieve significant data.
 149  *
 150  * LIMITATIONS:
 151  *
 152  * To keep down the amount of stack used by this function, the following limits
 153  * have been imposed:
 154  *
 155  *  (1) This won't handle datalen > 65535 without increasing the size of the
 156  *      cons stack elements and length_too_long checking.
 157  *
 158  *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
 159  *      constructed types exceeds this, the decode will fail.
 160  *
 161  *  (3) The SET type (not the SET OF type) isn't really supported as tracking
 162  *      what members of the set have been seen is a pain.
 163  */
 164 int asn1_ber_decoder(const struct asn1_decoder *decoder,
 165                      void *context,
 166                      const unsigned char *data,
 167                      size_t datalen)
 168 {
 169         const unsigned char *machine = decoder->machine;
 170         const asn1_action_t *actions = decoder->actions;
 171         size_t machlen = decoder->machlen;
 172         enum asn1_opcode op;
 173         unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
 174         const char *errmsg;
 175         size_t pc = 0, dp = 0, tdp = 0, len = 0;
 176         int ret;
 177
 178         unsigned char flags = 0;
 179 #define FLAG_INDEFINITE_LENGTH  0x01
 180 #define FLAG_MATCHED            0x02
 181 #define FLAG_LAST_MATCHED       0x04 /* Last tag matched */
 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 &&
 214                      flags & FLAG_MATCHED) ||
 215                     dp == datalen) {
 216                         flags &= ~FLAG_LAST_MATCHED;
 217                         pc += asn1_op_lengths[op];
 218                         goto next_op;
 219                 }
 220
 221                 flags = 0;
 222                 hdr = 2;
 223
 224                 /* Extract a tag from the data */
 225                 if (unlikely(dp >= datalen - 1))
 226                         goto data_overrun_error;
 227                 tag = data[dp++];
 228                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
 229                         goto long_tag_not_supported;
 230
 231                 if (op & ASN1_OP_MATCH__ANY) {
 232                         pr_debug("- any %02x\n", tag);
 233                 } else {
 234                         /* Extract the tag from the machine
 235                          * - Either CONS or PRIM are permitted in the data if
 236                          *   CONS is not set in the op stream, otherwise CONS
 237                          *   is mandatory.
 238                          */
 239                         optag = machine[pc + 1];
 240                         flags |= optag & FLAG_CONS;
 241
 242                         /* Determine whether the tag matched */
 243                         tmp = optag ^ tag;
 244                         tmp &= ~(optag & ASN1_CONS_BIT);
 245                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
 246                         if (tmp != 0) {
 247                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
 248                                 if (op & ASN1_OP_MATCH__SKIP) {
 249                                         pc += asn1_op_lengths[op];
 250                                         dp--;
 251                                         goto next_op;
 252                                 }
 253                                 goto tag_mismatch;
 254                         }
 255                 }
 256                 flags |= FLAG_MATCHED;
 257
 258                 len = data[dp++];
 259                 if (len > 0x7f) {
 260                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 261                                 /* Indefinite length */
 262                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
 263                                         goto indefinite_len_primitive;
 264                                 flags |= FLAG_INDEFINITE_LENGTH;
 265                                 if (unlikely(2 > datalen - dp))
 266                                         goto data_overrun_error;
 267                         } else {
 268                                 int n = len - 0x80;
 269                                 if (unlikely(n > 2))
 270                                         goto length_too_long;
 271                                 if (unlikely(dp >= datalen - n))
 272                                         goto data_overrun_error;
 273                                 hdr += n;
 274                                 for (len = 0; n > 0; n--) {
 275                                         len <<= 8;
 276                                         len |= data[dp++];
 277                                 }
 278                                 if (unlikely(len > datalen - dp))
 279                                         goto data_overrun_error;
 280                         }
 281                 }
 282
 283                 if (flags & FLAG_CONS) {
 284                         /* For expected compound forms, we stack the positions
 285                          * of the start and end of the data.
 286                          */
 287                         if (unlikely(csp >= NR_CONS_STACK))
 288                                 goto cons_stack_overflow;
 289                         cons_dp_stack[csp] = dp;
 290                         cons_hdrlen_stack[csp] = hdr;
 291                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 292                                 cons_datalen_stack[csp] = datalen;
 293                                 datalen = dp + len;
 294                         } else {
 295                                 cons_datalen_stack[csp] = 0;
 296                         }
 297                         csp++;
 298                 }
 299
 300                 pr_debug("- TAG: %02x %zu%s\n",
 301                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 302                 tdp = dp;
 303         }
 304
 305         /* Decide how to handle the operation */
 306         switch (op) {
 307         case ASN1_OP_MATCH_ANY_ACT:
 308         case ASN1_OP_COND_MATCH_ANY_ACT:
 309                 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
 310                 if (ret < 0)
 311                         return ret;
 312                 goto skip_data;
 313
 314         case ASN1_OP_MATCH_ACT:
 315         case ASN1_OP_MATCH_ACT_OR_SKIP:
 316         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 317                 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
 318                 if (ret < 0)
 319                         return ret;
 320                 goto skip_data;
 321
 322         case ASN1_OP_MATCH:
 323         case ASN1_OP_MATCH_OR_SKIP:
 324         case ASN1_OP_MATCH_ANY:
 325         case ASN1_OP_COND_MATCH_OR_SKIP:
 326         case ASN1_OP_COND_MATCH_ANY:
 327         skip_data:
 328                 if (!(flags & FLAG_CONS)) {
 329                         if (flags & FLAG_INDEFINITE_LENGTH) {
 330                                 ret = asn1_find_indefinite_length(
 331                                         data, datalen, &dp, &len, &errmsg);
 332                                 if (ret < 0)
 333                                         goto error;
 334                         } else {
 335                                 dp += len;
 336                         }
 337                         pr_debug("- LEAF: %zu\n", len);
 338                 }
 339                 pc += asn1_op_lengths[op];
 340                 goto next_op;
 341
 342         case ASN1_OP_MATCH_JUMP:
 343         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 344         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 345                 pr_debug("- MATCH_JUMP\n");
 346                 if (unlikely(jsp == NR_JUMP_STACK))
 347                         goto jump_stack_overflow;
 348                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 349                 pc = machine[pc + 2];
 350                 goto next_op;
 351
 352         case ASN1_OP_COND_FAIL:
 353                 if (unlikely(!(flags & FLAG_MATCHED)))
 354                         goto tag_mismatch;
 355                 pc += asn1_op_lengths[op];
 356                 goto next_op;
 357
 358         case ASN1_OP_COMPLETE:
 359                 if (unlikely(jsp != 0 || csp != 0)) {
 360                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 361                                jsp, csp);
 362                         return -EBADMSG;
 363                 }
 364                 return 0;
 365
 366         case ASN1_OP_END_SET:
 367         case ASN1_OP_END_SET_ACT:
 368                 if (unlikely(!(flags & FLAG_MATCHED)))
 369                         goto tag_mismatch;
 370         case ASN1_OP_END_SEQ:
 371         case ASN1_OP_END_SET_OF:
 372         case ASN1_OP_END_SEQ_OF:
 373         case ASN1_OP_END_SEQ_ACT:
 374         case ASN1_OP_END_SET_OF_ACT:
 375         case ASN1_OP_END_SEQ_OF_ACT:
 376                 if (unlikely(csp <= 0))
 377                         goto cons_stack_underflow;
 378                 csp--;
 379                 tdp = cons_dp_stack[csp];
 380                 hdr = cons_hdrlen_stack[csp];
 381                 len = datalen;
 382                 datalen = cons_datalen_stack[csp];
 383                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 384                          tdp, dp, len, datalen);
 385                 if (datalen == 0) {
 386                         /* Indefinite length - check for the EOC. */
 387                         datalen = len;
 388                         if (unlikely(datalen - dp < 2))
 389                                 goto data_overrun_error;
 390                         if (data[dp++] != 0) {
 391                                 if (op & ASN1_OP_END__OF) {
 392                                         dp--;
 393                                         csp++;
 394                                         pc = machine[pc + 1];
 395                                         pr_debug("- continue\n");
 396                                         goto next_op;
 397                                 }
 398                                 goto missing_eoc;
 399                         }
 400                         if (data[dp++] != 0)
 401                                 goto invalid_eoc;
 402                         len = dp - tdp - 2;
 403                 } else {
 404                         if (dp < len && (op & ASN1_OP_END__OF)) {
 405                                 datalen = len;
 406                                 csp++;
 407                                 pc = machine[pc + 1];
 408                                 pr_debug("- continue\n");
 409                                 goto next_op;
 410                         }
 411                         if (dp != len)
 412                                 goto cons_length_error;
 413                         len -= tdp;
 414                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 415                 }
 416
 417                 if (op & ASN1_OP_END__ACT) {
 418                         unsigned char act;
 419                         if (op & ASN1_OP_END__OF)
 420                                 act = machine[pc + 2];
 421                         else
 422                                 act = machine[pc + 1];
 423                         ret = actions[act](context, hdr, 0, data + tdp, len);
 424                 }
 425                 pc += asn1_op_lengths[op];
 426                 goto next_op;
 427
 428         case ASN1_OP_MAYBE_ACT:
 429                 if (!(flags & FLAG_LAST_MATCHED)) {
 430                         pc += asn1_op_lengths[op];
 431                         goto next_op;
 432                 }
 433         case ASN1_OP_ACT:
 434                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 435                 if (ret < 0)
 436                         return ret;
 437                 pc += asn1_op_lengths[op];
 438                 goto next_op;
 439
 440         case ASN1_OP_RETURN:
 441                 if (unlikely(jsp <= 0))
 442                         goto jump_stack_underflow;
 443                 pc = jump_stack[--jsp];
 444                 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
 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) pc=%zu\n",
 453                op, pc);
 454         return -EBADMSG;
 455
 456 data_overrun_error:
 457         errmsg = "Data overrun error";
 458         goto error;
 459 machine_overrun_error:
 460         errmsg = "Machine overrun error";
 461         goto error;
 462 jump_stack_underflow:
 463         errmsg = "Jump stack underflow";
 464         goto error;
 465 jump_stack_overflow:
 466         errmsg = "Jump stack overflow";
 467         goto error;
 468 cons_stack_underflow:
 469         errmsg = "Cons stack underflow";
 470         goto error;
 471 cons_stack_overflow:
 472         errmsg = "Cons stack overflow";
 473         goto error;
 474 cons_length_error:
 475         errmsg = "Cons length error";
 476         goto error;
 477 missing_eoc:
 478         errmsg = "Missing EOC in indefinite len cons";
 479         goto error;
 480 invalid_eoc:
 481         errmsg = "Invalid length EOC";
 482         goto error;
 483 length_too_long:
 484         errmsg = "Unsupported length";
 485         goto error;
 486 indefinite_len_primitive:
 487         errmsg = "Indefinite len primitive not permitted";
 488         goto error;
 489 tag_mismatch:
 490         errmsg = "Unexpected tag";
 491         goto error;
 492 long_tag_not_supported:
 493         errmsg = "Long tag not supported";
 494 error:
 495         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 496                  errmsg, pc, dp, optag, tag, len);
 497         return -EBADMSG;
 498 }
 499 EXPORT_SYMBOL_GPL(asn1_ber_decoder);