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