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