lib/asn1_decoder.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Decoder for ASN.1 BER/DER/CER encoded bytestream
   3  *
   4  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #ifdef __UBOOT__
   9 #include <linux/compat.h>
  10 #else
  11 #include <linux/export.h>
  12 #endif
  13 #include <linux/kernel.h>
  14 #include <linux/errno.h>
  15 #ifndef __UBOOT__
  16 #include <linux/module.h>
  17 #endif
  18 #include <linux/asn1_decoder.h>
  19 #include <linux/asn1_ber_bytecode.h>
  20
  21 static const unsigned char asn1_op_lengths[ASN1_OP__NR] = {
  22         /*                                      OPC TAG JMP ACT */
  23         [ASN1_OP_MATCH]                         = 1 + 1,
  24         [ASN1_OP_MATCH_OR_SKIP]                 = 1 + 1,
  25         [ASN1_OP_MATCH_ACT]                     = 1 + 1     + 1,
  26         [ASN1_OP_MATCH_ACT_OR_SKIP]             = 1 + 1     + 1,
  27         [ASN1_OP_MATCH_JUMP]                    = 1 + 1 + 1,
  28         [ASN1_OP_MATCH_JUMP_OR_SKIP]            = 1 + 1 + 1,
  29         [ASN1_OP_MATCH_ANY]                     = 1,
  30         [ASN1_OP_MATCH_ANY_OR_SKIP]             = 1,
  31         [ASN1_OP_MATCH_ANY_ACT]                 = 1         + 1,
  32         [ASN1_OP_MATCH_ANY_ACT_OR_SKIP]         = 1         + 1,
  33         [ASN1_OP_COND_MATCH_OR_SKIP]            = 1 + 1,
  34         [ASN1_OP_COND_MATCH_ACT_OR_SKIP]        = 1 + 1     + 1,
  35         [ASN1_OP_COND_MATCH_JUMP_OR_SKIP]       = 1 + 1 + 1,
  36         [ASN1_OP_COND_MATCH_ANY]                = 1,
  37         [ASN1_OP_COND_MATCH_ANY_OR_SKIP]        = 1,
  38         [ASN1_OP_COND_MATCH_ANY_ACT]            = 1         + 1,
  39         [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]    = 1         + 1,
  40         [ASN1_OP_COND_FAIL]                     = 1,
  41         [ASN1_OP_COMPLETE]                      = 1,
  42         [ASN1_OP_ACT]                           = 1         + 1,
  43         [ASN1_OP_MAYBE_ACT]                     = 1         + 1,
  44         [ASN1_OP_RETURN]                        = 1,
  45         [ASN1_OP_END_SEQ]                       = 1,
  46         [ASN1_OP_END_SEQ_OF]                    = 1     + 1,
  47         [ASN1_OP_END_SET]                       = 1,
  48         [ASN1_OP_END_SET_OF]                    = 1     + 1,
  49         [ASN1_OP_END_SEQ_ACT]                   = 1         + 1,
  50         [ASN1_OP_END_SEQ_OF_ACT]                = 1     + 1 + 1,
  51         [ASN1_OP_END_SET_ACT]                   = 1         + 1,
  52         [ASN1_OP_END_SET_OF_ACT]                = 1     + 1 + 1,
  53 };
  54
  55 /*
  56  * Find the length of an indefinite length object
  57  * @data: The data buffer
  58  * @datalen: The end of the innermost containing element in the buffer
  59  * @_dp: The data parse cursor (updated before returning)
  60  * @_len: Where to return the size of the element.
  61  * @_errmsg: Where to return a pointer to an error message on error
  62  */
  63 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
  64                                        size_t *_dp, size_t *_len,
  65                                        const char **_errmsg)
  66 {
  67         unsigned char tag, tmp;
  68         size_t dp = *_dp, len, n;
  69         int indef_level = 1;
  70
  71 next_tag:
  72         if (unlikely(datalen - dp < 2)) {
  73                 if (datalen == dp)
  74                         goto missing_eoc;
  75                 goto data_overrun_error;
  76         }
  77
  78         /* Extract a tag from the data */
  79         tag = data[dp++];
  80         if (tag == ASN1_EOC) {
  81                 /* It appears to be an EOC. */
  82                 if (data[dp++] != 0)
  83                         goto invalid_eoc;
  84                 if (--indef_level <= 0) {
  85                         *_len = dp - *_dp;
  86                         *_dp = dp;
  87                         return 0;
  88                 }
  89                 goto next_tag;
  90         }
  91
  92         if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
  93                 do {
  94                         if (unlikely(datalen - dp < 2))
  95                                 goto data_overrun_error;
  96                         tmp = data[dp++];
  97                 } while (tmp & 0x80);
  98         }
  99
 100         /* Extract the length */
 101         len = data[dp++];
 102         if (len <= 0x7f)
 103                 goto check_length;
 104
 105         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 106                 /* Indefinite length */
 107                 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
 108                         goto indefinite_len_primitive;
 109                 indef_level++;
 110                 goto next_tag;
 111         }
 112
 113         n = len - 0x80;
 114         if (unlikely(n > sizeof(len) - 1))
 115                 goto length_too_long;
 116         if (unlikely(n > datalen - dp))
 117                 goto data_overrun_error;
 118         len = 0;
 119         for (; n > 0; n--) {
 120                 len <<= 8;
 121                 len |= data[dp++];
 122         }
 123 check_length:
 124         if (len > datalen - dp)
 125                 goto data_overrun_error;
 126         dp += len;
 127         goto next_tag;
 128
 129 length_too_long:
 130         *_errmsg = "Unsupported length";
 131         goto error;
 132 indefinite_len_primitive:
 133         *_errmsg = "Indefinite len primitive not permitted";
 134         goto error;
 135 invalid_eoc:
 136         *_errmsg = "Invalid length EOC";
 137         goto error;
 138 data_overrun_error:
 139         *_errmsg = "Data overrun error";
 140         goto error;
 141 missing_eoc:
 142         *_errmsg = "Missing EOC in indefinite len cons";
 143 error:
 144         *_dp = dp;
 145         return -1;
 146 }
 147
 148 /**
 149  * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
 150  * @decoder: The decoder definition (produced by asn1_compiler)
 151  * @context: The caller's context (to be passed to the action functions)
 152  * @data: The encoded data
 153  * @datalen: The size of the encoded data
 154  *
 155  * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
 156  * produced by asn1_compiler.  Action functions are called on marked tags to
 157  * allow the caller to retrieve significant data.
 158  *
 159  * LIMITATIONS:
 160  *
 161  * To keep down the amount of stack used by this function, the following limits
 162  * have been imposed:
 163  *
 164  *  (1) This won't handle datalen > 65535 without increasing the size of the
 165  *      cons stack elements and length_too_long checking.
 166  *
 167  *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
 168  *      constructed types exceeds this, the decode will fail.
 169  *
 170  *  (3) The SET type (not the SET OF type) isn't really supported as tracking
 171  *      what members of the set have been seen is a pain.
 172  */
 173 int asn1_ber_decoder(const struct asn1_decoder *decoder,
 174                      void *context,
 175                      const unsigned char *data,
 176                      size_t datalen)
 177 {
 178         const unsigned char *machine = decoder->machine;
 179         const asn1_action_t *actions = decoder->actions;
 180         size_t machlen = decoder->machlen;
 181         enum asn1_opcode op;
 182         unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
 183         const char *errmsg;
 184         size_t pc = 0, dp = 0, tdp = 0, len = 0;
 185         int ret;
 186
 187         unsigned char flags = 0;
 188 #define FLAG_INDEFINITE_LENGTH  0x01
 189 #define FLAG_MATCHED            0x02
 190 #define FLAG_LAST_MATCHED       0x04 /* Last tag matched */
 191 #define FLAG_CONS               0x20 /* Corresponds to CONS bit in the opcode tag
 192                                       * - ie. whether or not we are going to parse
 193                                       *   a compound type.
 194                                       */
 195
 196 #define NR_CONS_STACK 10
 197         unsigned short cons_dp_stack[NR_CONS_STACK];
 198         unsigned short cons_datalen_stack[NR_CONS_STACK];
 199         unsigned char cons_hdrlen_stack[NR_CONS_STACK];
 200 #define NR_JUMP_STACK 10
 201         unsigned char jump_stack[NR_JUMP_STACK];
 202
 203         if (datalen > 65535)
 204                 return -EMSGSIZE;
 205
 206 next_op:
 207         pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
 208                  pc, machlen, dp, datalen, csp, jsp);
 209         if (unlikely(pc >= machlen))
 210                 goto machine_overrun_error;
 211         op = machine[pc];
 212         if (unlikely(pc + asn1_op_lengths[op] > machlen))
 213                 goto machine_overrun_error;
 214
 215         /* If this command is meant to match a tag, then do that before
 216          * evaluating the command.
 217          */
 218         if (op <= ASN1_OP__MATCHES_TAG) {
 219                 unsigned char tmp;
 220
 221                 /* Skip conditional matches if possible */
 222                 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) ||
 223                     (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
 224                         flags &= ~FLAG_LAST_MATCHED;
 225                         pc += asn1_op_lengths[op];
 226                         goto next_op;
 227                 }
 228
 229                 flags = 0;
 230                 hdr = 2;
 231
 232                 /* Extract a tag from the data */
 233                 if (unlikely(datalen - dp < 2))
 234                         goto data_overrun_error;
 235                 tag = data[dp++];
 236                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
 237                         goto long_tag_not_supported;
 238
 239                 if (op & ASN1_OP_MATCH__ANY) {
 240                         pr_debug("- any %02x\n", tag);
 241                 } else {
 242                         /* Extract the tag from the machine
 243                          * - Either CONS or PRIM are permitted in the data if
 244                          *   CONS is not set in the op stream, otherwise CONS
 245                          *   is mandatory.
 246                          */
 247                         optag = machine[pc + 1];
 248                         flags |= optag & FLAG_CONS;
 249
 250                         /* Determine whether the tag matched */
 251                         tmp = optag ^ tag;
 252                         tmp &= ~(optag & ASN1_CONS_BIT);
 253                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
 254                         if (tmp != 0) {
 255                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
 256                                 if (op & ASN1_OP_MATCH__SKIP) {
 257                                         pc += asn1_op_lengths[op];
 258                                         dp--;
 259                                         goto next_op;
 260                                 }
 261                                 goto tag_mismatch;
 262                         }
 263                 }
 264                 flags |= FLAG_MATCHED;
 265
 266                 len = data[dp++];
 267                 if (len > 0x7f) {
 268                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 269                                 /* Indefinite length */
 270                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
 271                                         goto indefinite_len_primitive;
 272                                 flags |= FLAG_INDEFINITE_LENGTH;
 273                                 if (unlikely(2 > datalen - dp))
 274                                         goto data_overrun_error;
 275                         } else {
 276                                 int n = len - 0x80;
 277                                 if (unlikely(n > 2))
 278                                         goto length_too_long;
 279                                 if (unlikely(n > datalen - dp))
 280                                         goto data_overrun_error;
 281                                 hdr += n;
 282                                 for (len = 0; n > 0; n--) {
 283                                         len <<= 8;
 284                                         len |= data[dp++];
 285                                 }
 286                                 if (unlikely(len > datalen - dp))
 287                                         goto data_overrun_error;
 288                         }
 289                 } else {
 290                         if (unlikely(len > datalen - dp))
 291                                 goto data_overrun_error;
 292                 }
 293
 294                 if (flags & FLAG_CONS) {
 295                         /* For expected compound forms, we stack the positions
 296                          * of the start and end of the data.
 297                          */
 298                         if (unlikely(csp >= NR_CONS_STACK))
 299                                 goto cons_stack_overflow;
 300                         cons_dp_stack[csp] = dp;
 301                         cons_hdrlen_stack[csp] = hdr;
 302                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
 303                                 cons_datalen_stack[csp] = datalen;
 304                                 datalen = dp + len;
 305                         } else {
 306                                 cons_datalen_stack[csp] = 0;
 307                         }
 308                         csp++;
 309                 }
 310
 311                 pr_debug("- TAG: %02x %zu%s\n",
 312                          tag, len, flags & FLAG_CONS ? " CONS" : "");
 313                 tdp = dp;
 314         }
 315
 316         /* Decide how to handle the operation */
 317         switch (op) {
 318         case ASN1_OP_MATCH:
 319         case ASN1_OP_MATCH_OR_SKIP:
 320         case ASN1_OP_MATCH_ACT:
 321         case ASN1_OP_MATCH_ACT_OR_SKIP:
 322         case ASN1_OP_MATCH_ANY:
 323         case ASN1_OP_MATCH_ANY_OR_SKIP:
 324         case ASN1_OP_MATCH_ANY_ACT:
 325         case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
 326         case ASN1_OP_COND_MATCH_OR_SKIP:
 327         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
 328         case ASN1_OP_COND_MATCH_ANY:
 329         case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
 330         case ASN1_OP_COND_MATCH_ANY_ACT:
 331         case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
 332
 333                 if (!(flags & FLAG_CONS)) {
 334                         if (flags & FLAG_INDEFINITE_LENGTH) {
 335                                 size_t tmp = dp;
 336
 337                                 ret = asn1_find_indefinite_length(
 338                                         data, datalen, &tmp, &len, &errmsg);
 339                                 if (ret < 0)
 340                                         goto error;
 341                         }
 342                         pr_debug("- LEAF: %zu\n", len);
 343                 }
 344
 345                 if (op & ASN1_OP_MATCH__ACT) {
 346                         unsigned char act;
 347
 348                         if (op & ASN1_OP_MATCH__ANY)
 349                                 act = machine[pc + 1];
 350                         else
 351                                 act = machine[pc + 2];
 352                         ret = actions[act](context, hdr, tag, data + dp, len);
 353                         if (ret < 0)
 354                                 return ret;
 355                 }
 356
 357                 if (!(flags & FLAG_CONS))
 358                         dp += len;
 359                 pc += asn1_op_lengths[op];
 360                 goto next_op;
 361
 362         case ASN1_OP_MATCH_JUMP:
 363         case ASN1_OP_MATCH_JUMP_OR_SKIP:
 364         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
 365                 pr_debug("- MATCH_JUMP\n");
 366                 if (unlikely(jsp == NR_JUMP_STACK))
 367                         goto jump_stack_overflow;
 368                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
 369                 pc = machine[pc + 2];
 370                 goto next_op;
 371
 372         case ASN1_OP_COND_FAIL:
 373                 if (unlikely(!(flags & FLAG_MATCHED)))
 374                         goto tag_mismatch;
 375                 pc += asn1_op_lengths[op];
 376                 goto next_op;
 377
 378         case ASN1_OP_COMPLETE:
 379                 if (unlikely(jsp != 0 || csp != 0)) {
 380                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
 381                                jsp, csp);
 382                         return -EBADMSG;
 383                 }
 384                 return 0;
 385
 386         case ASN1_OP_END_SET:
 387         case ASN1_OP_END_SET_ACT:
 388                 if (unlikely(!(flags & FLAG_MATCHED)))
 389                         goto tag_mismatch;
 390                 /* fall through */
 391
 392         case ASN1_OP_END_SEQ:
 393         case ASN1_OP_END_SET_OF:
 394         case ASN1_OP_END_SEQ_OF:
 395         case ASN1_OP_END_SEQ_ACT:
 396         case ASN1_OP_END_SET_OF_ACT:
 397         case ASN1_OP_END_SEQ_OF_ACT:
 398                 if (unlikely(csp <= 0))
 399                         goto cons_stack_underflow;
 400                 csp--;
 401                 tdp = cons_dp_stack[csp];
 402                 hdr = cons_hdrlen_stack[csp];
 403                 len = datalen;
 404                 datalen = cons_datalen_stack[csp];
 405                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
 406                          tdp, dp, len, datalen);
 407                 if (datalen == 0) {
 408                         /* Indefinite length - check for the EOC. */
 409                         datalen = len;
 410                         if (unlikely(datalen - dp < 2))
 411                                 goto data_overrun_error;
 412                         if (data[dp++] != 0) {
 413                                 if (op & ASN1_OP_END__OF) {
 414                                         dp--;
 415                                         csp++;
 416                                         pc = machine[pc + 1];
 417                                         pr_debug("- continue\n");
 418                                         goto next_op;
 419                                 }
 420                                 goto missing_eoc;
 421                         }
 422                         if (data[dp++] != 0)
 423                                 goto invalid_eoc;
 424                         len = dp - tdp - 2;
 425                 } else {
 426                         if (dp < len && (op & ASN1_OP_END__OF)) {
 427                                 datalen = len;
 428                                 csp++;
 429                                 pc = machine[pc + 1];
 430                                 pr_debug("- continue\n");
 431                                 goto next_op;
 432                         }
 433                         if (dp != len)
 434                                 goto cons_length_error;
 435                         len -= tdp;
 436                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
 437                 }
 438
 439                 if (op & ASN1_OP_END__ACT) {
 440                         unsigned char act;
 441                         if (op & ASN1_OP_END__OF)
 442                                 act = machine[pc + 2];
 443                         else
 444                                 act = machine[pc + 1];
 445                         ret = actions[act](context, hdr, 0, data + tdp, len);
 446                         if (ret < 0)
 447                                 return ret;
 448                 }
 449                 pc += asn1_op_lengths[op];
 450                 goto next_op;
 451
 452         case ASN1_OP_MAYBE_ACT:
 453                 if (!(flags & FLAG_LAST_MATCHED)) {
 454                         pc += asn1_op_lengths[op];
 455                         goto next_op;
 456                 }
 457                 /* fall through */
 458
 459         case ASN1_OP_ACT:
 460                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 461                 if (ret < 0)
 462                         return ret;
 463                 pc += asn1_op_lengths[op];
 464                 goto next_op;
 465
 466         case ASN1_OP_RETURN:
 467                 if (unlikely(jsp <= 0))
 468                         goto jump_stack_underflow;
 469                 pc = jump_stack[--jsp];
 470                 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
 471                 goto next_op;
 472
 473         default:
 474                 break;
 475         }
 476
 477         /* Shouldn't reach here */
 478         pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n",
 479                op, pc);
 480         return -EBADMSG;
 481
 482 data_overrun_error:
 483         errmsg = "Data overrun error";
 484         goto error;
 485 machine_overrun_error:
 486         errmsg = "Machine overrun error";
 487         goto error;
 488 jump_stack_underflow:
 489         errmsg = "Jump stack underflow";
 490         goto error;
 491 jump_stack_overflow:
 492         errmsg = "Jump stack overflow";
 493         goto error;
 494 cons_stack_underflow:
 495         errmsg = "Cons stack underflow";
 496         goto error;
 497 cons_stack_overflow:
 498         errmsg = "Cons stack overflow";
 499         goto error;
 500 cons_length_error:
 501         errmsg = "Cons length error";
 502         goto error;
 503 missing_eoc:
 504         errmsg = "Missing EOC in indefinite len cons";
 505         goto error;
 506 invalid_eoc:
 507         errmsg = "Invalid length EOC";
 508         goto error;
 509 length_too_long:
 510         errmsg = "Unsupported length";
 511         goto error;
 512 indefinite_len_primitive:
 513         errmsg = "Indefinite len primitive not permitted";
 514         goto error;
 515 tag_mismatch:
 516         errmsg = "Unexpected tag";
 517         goto error;
 518 long_tag_not_supported:
 519         errmsg = "Long tag not supported";
 520 error:
 521         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
 522                  errmsg, pc, dp, optag, tag, len);
 523         return -EBADMSG;
 524 }
 525 EXPORT_SYMBOL_GPL(asn1_ber_decoder);
 526
 527 MODULE_LICENSE("GPL");