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