linux/lib/asn1_decoder.c
<<
>>
Prefs
   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
  18static 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 */
  55static 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
  63next_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
 119length_too_long:
 120        *_errmsg = "Unsupported length";
 121        goto error;
 122indefinite_len_primitive:
 123        *_errmsg = "Indefinite len primitive not permitted";
 124        goto error;
 125invalid_eoc:
 126        *_errmsg = "Invalid length EOC";
 127        goto error;
 128data_overrun_error:
 129        *_errmsg = "Data overrun error";
 130        goto error;
 131missing_eoc:
 132        *_errmsg = "Missing EOC in indefinite len cons";
 133error:
 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 */
 163int 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
 195next_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
 444data_overrun_error:
 445        errmsg = "Data overrun error";
 446        goto error;
 447machine_overrun_error:
 448        errmsg = "Machine overrun error";
 449        goto error;
 450jump_stack_underflow:
 451        errmsg = "Jump stack underflow";
 452        goto error;
 453jump_stack_overflow:
 454        errmsg = "Jump stack overflow";
 455        goto error;
 456cons_stack_underflow:
 457        errmsg = "Cons stack underflow";
 458        goto error;
 459cons_stack_overflow:
 460        errmsg = "Cons stack overflow";
 461        goto error;
 462cons_length_error:
 463        errmsg = "Cons length error";
 464        goto error;
 465missing_eoc:
 466        errmsg = "Missing EOC in indefinite len cons";
 467        goto error;
 468invalid_eoc:
 469        errmsg = "Invalid length EOC";
 470        goto error;
 471length_too_long:
 472        errmsg = "Unsupported length";
 473        goto error;
 474indefinite_len_primitive:
 475        errmsg = "Indefinite len primitive not permitted";
 476        goto error;
 477tag_mismatch:
 478        errmsg = "Unexpected tag";
 479        goto error;
 480long_tag_not_supported:
 481        errmsg = "Long tag not supported";
 482error:
 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}
 487EXPORT_SYMBOL_GPL(asn1_ber_decoder);
 488
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.