lib/xz/xz_dec_stream.c

   1 /*
   2  * .xz Stream decoder
   3  *
   4  * Author: Lasse Collin <lasse.collin@tukaani.org>
   5  *
   6  * This file has been put into the public domain.
   7  * You can do whatever you want with this file.
   8  */
   9
  10 #include "xz_private.h"
  11 #include "xz_stream.h"
  12
  13 /* Hash used to validate the Index field */
  14 struct xz_dec_hash {
  15         vli_type unpadded;
  16         vli_type uncompressed;
  17         uint32_t crc32;
  18 };
  19
  20 struct xz_dec {
  21         /* Position in dec_main() */
  22         enum {
  23                 SEQ_STREAM_HEADER,
  24                 SEQ_BLOCK_START,
  25                 SEQ_BLOCK_HEADER,
  26                 SEQ_BLOCK_UNCOMPRESS,
  27                 SEQ_BLOCK_PADDING,
  28                 SEQ_BLOCK_CHECK,
  29                 SEQ_INDEX,
  30                 SEQ_INDEX_PADDING,
  31                 SEQ_INDEX_CRC32,
  32                 SEQ_STREAM_FOOTER
  33         } sequence;
  34
  35         /* Position in variable-length integers and Check fields */
  36         uint32_t pos;
  37
  38         /* Variable-length integer decoded by dec_vli() */
  39         vli_type vli;
  40
  41         /* Saved in_pos and out_pos */
  42         size_t in_start;
  43         size_t out_start;
  44
  45         /* CRC32 value in Block or Index */
  46         uint32_t crc32;
  47
  48         /* Type of the integrity check calculated from uncompressed data */
  49         enum xz_check check_type;
  50
  51         /* Operation mode */
  52         enum xz_mode mode;
  53
  54         /*
  55          * True if the next call to xz_dec_run() is allowed to return
  56          * XZ_BUF_ERROR.
  57          */
  58         bool allow_buf_error;
  59
  60         /* Information stored in Block Header */
  61         struct {
  62                 /*
  63                  * Value stored in the Compressed Size field, or
  64                  * VLI_UNKNOWN if Compressed Size is not present.
  65                  */
  66                 vli_type compressed;
  67
  68                 /*
  69                  * Value stored in the Uncompressed Size field, or
  70                  * VLI_UNKNOWN if Uncompressed Size is not present.
  71                  */
  72                 vli_type uncompressed;
  73
  74                 /* Size of the Block Header field */
  75                 uint32_t size;
  76         } block_header;
  77
  78         /* Information collected when decoding Blocks */
  79         struct {
  80                 /* Observed compressed size of the current Block */
  81                 vli_type compressed;
  82
  83                 /* Observed uncompressed size of the current Block */
  84                 vli_type uncompressed;
  85
  86                 /* Number of Blocks decoded so far */
  87                 vli_type count;
  88
  89                 /*
  90                  * Hash calculated from the Block sizes. This is used to
  91                  * validate the Index field.
  92                  */
  93                 struct xz_dec_hash hash;
  94         } block;
  95
  96         /* Variables needed when verifying the Index field */
  97         struct {
  98                 /* Position in dec_index() */
  99                 enum {
 100                         SEQ_INDEX_COUNT,
 101                         SEQ_INDEX_UNPADDED,
 102                         SEQ_INDEX_UNCOMPRESSED
 103                 } sequence;
 104
 105                 /* Size of the Index in bytes */
 106                 vli_type size;
 107
 108                 /* Number of Records (matches block.count in valid files) */
 109                 vli_type count;
 110
 111                 /*
 112                  * Hash calculated from the Records (matches block.hash in
 113                  * valid files).
 114                  */
 115                 struct xz_dec_hash hash;
 116         } index;
 117
 118         /*
 119          * Temporary buffer needed to hold Stream Header, Block Header,
 120          * and Stream Footer. The Block Header is the biggest (1 KiB)
 121          * so we reserve space according to that. buf[] has to be aligned
 122          * to a multiple of four bytes; the size_t variables before it
 123          * should guarantee this.
 124          */
 125         struct {
 126                 size_t pos;
 127                 size_t size;
 128                 uint8_t buf[1024];
 129         } temp;
 130
 131         struct xz_dec_lzma2 *lzma2;
 132
 133 #ifdef XZ_DEC_BCJ
 134         struct xz_dec_bcj *bcj;
 135         bool bcj_active;
 136 #endif
 137 };
 138
 139 #ifdef XZ_DEC_ANY_CHECK
 140 /* Sizes of the Check field with different Check IDs */
 141 static const uint8_t check_sizes[16] = {
 142         0,
 143         4, 4, 4,
 144         8, 8, 8,
 145         16, 16, 16,
 146         32, 32, 32,
 147         64, 64, 64
 148 };
 149 #endif
 150
 151 /*
 152  * Fill s->temp by copying data starting from b->in[b->in_pos]. Caller
 153  * must have set s->temp.pos to indicate how much data we are supposed
 154  * to copy into s->temp.buf. Return true once s->temp.pos has reached
 155  * s->temp.size.
 156  */
 157 static bool fill_temp(struct xz_dec *s, struct xz_buf *b)
 158 {
 159         size_t copy_size = min_t(size_t,
 160                         b->in_size - b->in_pos, s->temp.size - s->temp.pos);
 161
 162         memcpy(s->temp.buf + s->temp.pos, b->in + b->in_pos, copy_size);
 163         b->in_pos += copy_size;
 164         s->temp.pos += copy_size;
 165
 166         if (s->temp.pos == s->temp.size) {
 167                 s->temp.pos = 0;
 168                 return true;
 169         }
 170
 171         return false;
 172 }
 173
 174 /* Decode a variable-length integer (little-endian base-128 encoding) */
 175 static enum xz_ret dec_vli(struct xz_dec *s, const uint8_t *in,
 176                            size_t *in_pos, size_t in_size)
 177 {
 178         uint8_t byte;
 179
 180         if (s->pos == 0)
 181                 s->vli = 0;
 182
 183         while (*in_pos < in_size) {
 184                 byte = in[*in_pos];
 185                 ++*in_pos;
 186
 187                 s->vli |= (vli_type)(byte & 0x7F) << s->pos;
 188
 189                 if ((byte & 0x80) == 0) {
 190                         /* Don't allow non-minimal encodings. */
 191                         if (byte == 0 && s->pos != 0)
 192                                 return XZ_DATA_ERROR;
 193
 194                         s->pos = 0;
 195                         return XZ_STREAM_END;
 196                 }
 197
 198                 s->pos += 7;
 199                 if (s->pos == 7 * VLI_BYTES_MAX)
 200                         return XZ_DATA_ERROR;
 201         }
 202
 203         return XZ_OK;
 204 }
 205
 206 /*
 207  * Decode the Compressed Data field from a Block. Update and validate
 208  * the observed compressed and uncompressed sizes of the Block so that
 209  * they don't exceed the values possibly stored in the Block Header
 210  * (validation assumes that no integer overflow occurs, since vli_type
 211  * is normally uint64_t). Update the CRC32 if presence of the CRC32
 212  * field was indicated in Stream Header.
 213  *
 214  * Once the decoding is finished, validate that the observed sizes match
 215  * the sizes possibly stored in the Block Header. Update the hash and
 216  * Block count, which are later used to validate the Index field.
 217  */
 218 static enum xz_ret dec_block(struct xz_dec *s, struct xz_buf *b)
 219 {
 220         enum xz_ret ret;
 221
 222         s->in_start = b->in_pos;
 223         s->out_start = b->out_pos;
 224
 225 #ifdef XZ_DEC_BCJ
 226         if (s->bcj_active)
 227                 ret = xz_dec_bcj_run(s->bcj, s->lzma2, b);
 228         else
 229 #endif
 230                 ret = xz_dec_lzma2_run(s->lzma2, b);
 231
 232         s->block.compressed += b->in_pos - s->in_start;
 233         s->block.uncompressed += b->out_pos - s->out_start;
 234
 235         /*
 236          * There is no need to separately check for VLI_UNKNOWN, since
 237          * the observed sizes are always smaller than VLI_UNKNOWN.
 238          */
 239         if (s->block.compressed > s->block_header.compressed
 240                         || s->block.uncompressed
 241                                 > s->block_header.uncompressed)
 242                 return XZ_DATA_ERROR;
 243
 244         if (s->check_type == XZ_CHECK_CRC32)
 245                 s->crc32 = xz_crc32(b->out + s->out_start,
 246                                 b->out_pos - s->out_start, s->crc32);
 247
 248         if (ret == XZ_STREAM_END) {
 249                 if (s->block_header.compressed != VLI_UNKNOWN
 250                                 && s->block_header.compressed
 251                                         != s->block.compressed)
 252                         return XZ_DATA_ERROR;
 253
 254                 if (s->block_header.uncompressed != VLI_UNKNOWN
 255                                 && s->block_header.uncompressed
 256                                         != s->block.uncompressed)
 257                         return XZ_DATA_ERROR;
 258
 259                 s->block.hash.unpadded += s->block_header.size
 260                                 + s->block.compressed;
 261
 262 #ifdef XZ_DEC_ANY_CHECK
 263                 s->block.hash.unpadded += check_sizes[s->check_type];
 264 #else
 265                 if (s->check_type == XZ_CHECK_CRC32)
 266                         s->block.hash.unpadded += 4;
 267 #endif
 268
 269                 s->block.hash.uncompressed += s->block.uncompressed;
 270                 s->block.hash.crc32 = xz_crc32(
 271                                 (const uint8_t *)&s->block.hash,
 272                                 sizeof(s->block.hash), s->block.hash.crc32);
 273
 274                 ++s->block.count;
 275         }
 276
 277         return ret;
 278 }
 279
 280 /* Update the Index size and the CRC32 value. */
 281 static void index_update(struct xz_dec *s, const struct xz_buf *b)
 282 {
 283         size_t in_used = b->in_pos - s->in_start;
 284         s->index.size += in_used;
 285         s->crc32 = xz_crc32(b->in + s->in_start, in_used, s->crc32);
 286 }
 287
 288 /*
 289  * Decode the Number of Records, Unpadded Size, and Uncompressed Size
 290  * fields from the Index field. That is, Index Padding and CRC32 are not
 291  * decoded by this function.
 292  *
 293  * This can return XZ_OK (more input needed), XZ_STREAM_END (everything
 294  * successfully decoded), or XZ_DATA_ERROR (input is corrupt).
 295  */
 296 static enum xz_ret dec_index(struct xz_dec *s, struct xz_buf *b)
 297 {
 298         enum xz_ret ret;
 299
 300         do {
 301                 ret = dec_vli(s, b->in, &b->in_pos, b->in_size);
 302                 if (ret != XZ_STREAM_END) {
 303                         index_update(s, b);
 304                         return ret;
 305                 }
 306
 307                 switch (s->index.sequence) {
 308                 case SEQ_INDEX_COUNT:
 309                         s->index.count = s->vli;
 310
 311                         /*
 312                          * Validate that the Number of Records field
 313                          * indicates the same number of Records as
 314                          * there were Blocks in the Stream.
 315                          */
 316                         if (s->index.count != s->block.count)
 317                                 return XZ_DATA_ERROR;
 318
 319                         s->index.sequence = SEQ_INDEX_UNPADDED;
 320                         break;
 321
 322                 case SEQ_INDEX_UNPADDED:
 323                         s->index.hash.unpadded += s->vli;
 324                         s->index.sequence = SEQ_INDEX_UNCOMPRESSED;
 325                         break;
 326
 327                 case SEQ_INDEX_UNCOMPRESSED:
 328                         s->index.hash.uncompressed += s->vli;
 329                         s->index.hash.crc32 = xz_crc32(
 330                                         (const uint8_t *)&s->index.hash,
 331                                         sizeof(s->index.hash),
 332                                         s->index.hash.crc32);
 333                         --s->index.count;
 334                         s->index.sequence = SEQ_INDEX_UNPADDED;
 335                         break;
 336                 }
 337         } while (s->index.count > 0);
 338
 339         return XZ_STREAM_END;
 340 }
 341
 342 /*
 343  * Validate that the next four input bytes match the value of s->crc32.
 344  * s->pos must be zero when starting to validate the first byte.
 345  */
 346 static enum xz_ret crc32_validate(struct xz_dec *s, struct xz_buf *b)
 347 {
 348         do {
 349                 if (b->in_pos == b->in_size)
 350                         return XZ_OK;
 351
 352                 if (((s->crc32 >> s->pos) & 0xFF) != b->in[b->in_pos++])
 353                         return XZ_DATA_ERROR;
 354
 355                 s->pos += 8;
 356
 357         } while (s->pos < 32);
 358
 359         s->crc32 = 0;
 360         s->pos = 0;
 361
 362         return XZ_STREAM_END;
 363 }
 364
 365 #ifdef XZ_DEC_ANY_CHECK
 366 /*
 367  * Skip over the Check field when the Check ID is not supported.
 368  * Returns true once the whole Check field has been skipped over.
 369  */
 370 static bool check_skip(struct xz_dec *s, struct xz_buf *b)
 371 {
 372         while (s->pos < check_sizes[s->check_type]) {
 373                 if (b->in_pos == b->in_size)
 374                         return false;
 375
 376                 ++b->in_pos;
 377                 ++s->pos;
 378         }
 379
 380         s->pos = 0;
 381
 382         return true;
 383 }
 384 #endif
 385
 386 /* Decode the Stream Header field (the first 12 bytes of the .xz Stream). */
 387 static enum xz_ret dec_stream_header(struct xz_dec *s)
 388 {
 389         if (!memeq(s->temp.buf, HEADER_MAGIC, HEADER_MAGIC_SIZE))
 390                 return XZ_FORMAT_ERROR;
 391
 392         if (xz_crc32(s->temp.buf + HEADER_MAGIC_SIZE, 2, 0)
 393                         != get_le32(s->temp.buf + HEADER_MAGIC_SIZE + 2))
 394                 return XZ_DATA_ERROR;
 395
 396         if (s->temp.buf[HEADER_MAGIC_SIZE] != 0)
 397                 return XZ_OPTIONS_ERROR;
 398
 399         /*
 400          * Of integrity checks, we support only none (Check ID = 0) and
 401          * CRC32 (Check ID = 1). However, if XZ_DEC_ANY_CHECK is defined,
 402          * we will accept other check types too, but then the check won't
 403          * be verified and a warning (XZ_UNSUPPORTED_CHECK) will be given.
 404          */
 405         s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];
 406
 407 #ifdef XZ_DEC_ANY_CHECK
 408         if (s->check_type > XZ_CHECK_MAX)
 409                 return XZ_OPTIONS_ERROR;
 410
 411         if (s->check_type > XZ_CHECK_CRC32)
 412                 return XZ_UNSUPPORTED_CHECK;
 413 #else
 414         if (s->check_type > XZ_CHECK_CRC32)
 415                 return XZ_OPTIONS_ERROR;
 416 #endif
 417
 418         return XZ_OK;
 419 }
 420
 421 /* Decode the Stream Footer field (the last 12 bytes of the .xz Stream) */
 422 static enum xz_ret dec_stream_footer(struct xz_dec *s)
 423 {
 424         if (!memeq(s->temp.buf + 10, FOOTER_MAGIC, FOOTER_MAGIC_SIZE))
 425                 return XZ_DATA_ERROR;
 426
 427         if (xz_crc32(s->temp.buf + 4, 6, 0) != get_le32(s->temp.buf))
 428                 return XZ_DATA_ERROR;
 429
 430         /*
 431          * Validate Backward Size. Note that we never added the size of the
 432          * Index CRC32 field to s->index.size, thus we use s->index.size / 4
 433          * instead of s->index.size / 4 - 1.
 434          */
 435         if ((s->index.size >> 2) != get_le32(s->temp.buf + 4))
 436                 return XZ_DATA_ERROR;
 437
 438         if (s->temp.buf[8] != 0 || s->temp.buf[9] != s->check_type)
 439                 return XZ_DATA_ERROR;
 440
 441         /*
 442          * Use XZ_STREAM_END instead of XZ_OK to be more convenient
 443          * for the caller.
 444          */
 445         return XZ_STREAM_END;
 446 }
 447
 448 /* Decode the Block Header and initialize the filter chain. */
 449 static enum xz_ret dec_block_header(struct xz_dec *s)
 450 {
 451         enum xz_ret ret;
 452
 453         /*
 454          * Validate the CRC32. We know that the temp buffer is at least
 455          * eight bytes so this is safe.
 456          */
 457         s->temp.size -= 4;
 458         if (xz_crc32(s->temp.buf, s->temp.size, 0)
 459                         != get_le32(s->temp.buf + s->temp.size))
 460                 return XZ_DATA_ERROR;
 461
 462         s->temp.pos = 2;
 463
 464         /*
 465          * Catch unsupported Block Flags. We support only one or two filters
 466          * in the chain, so we catch that with the same test.
 467          */
 468 #ifdef XZ_DEC_BCJ
 469         if (s->temp.buf[1] & 0x3E)
 470 #else
 471         if (s->temp.buf[1] & 0x3F)
 472 #endif
 473                 return XZ_OPTIONS_ERROR;
 474
 475         /* Compressed Size */
 476         if (s->temp.buf[1] & 0x40) {
 477                 if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
 478                                         != XZ_STREAM_END)
 479                         return XZ_DATA_ERROR;
 480
 481                 s->block_header.compressed = s->vli;
 482         } else {
 483                 s->block_header.compressed = VLI_UNKNOWN;
 484         }
 485
 486         /* Uncompressed Size */
 487         if (s->temp.buf[1] & 0x80) {
 488                 if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
 489                                 != XZ_STREAM_END)
 490                         return XZ_DATA_ERROR;
 491
 492                 s->block_header.uncompressed = s->vli;
 493         } else {
 494                 s->block_header.uncompressed = VLI_UNKNOWN;
 495         }
 496
 497 #ifdef XZ_DEC_BCJ
 498         /* If there are two filters, the first one must be a BCJ filter. */
 499         s->bcj_active = s->temp.buf[1] & 0x01;
 500         if (s->bcj_active) {
 501                 if (s->temp.size - s->temp.pos < 2)
 502                         return XZ_OPTIONS_ERROR;
 503
 504                 ret = xz_dec_bcj_reset(s->bcj, s->temp.buf[s->temp.pos++]);
 505                 if (ret != XZ_OK)
 506                         return ret;
 507
 508                 /*
 509                  * We don't support custom start offset,
 510                  * so Size of Properties must be zero.
 511                  */
 512                 if (s->temp.buf[s->temp.pos++] != 0x00)
 513                         return XZ_OPTIONS_ERROR;
 514         }
 515 #endif
 516
 517         /* Valid Filter Flags always take at least two bytes. */
 518         if (s->temp.size - s->temp.pos < 2)
 519                 return XZ_DATA_ERROR;
 520
 521         /* Filter ID = LZMA2 */
 522         if (s->temp.buf[s->temp.pos++] != 0x21)
 523                 return XZ_OPTIONS_ERROR;
 524
 525         /* Size of Properties = 1-byte Filter Properties */
 526         if (s->temp.buf[s->temp.pos++] != 0x01)
 527                 return XZ_OPTIONS_ERROR;
 528
 529         /* Filter Properties contains LZMA2 dictionary size. */
 530         if (s->temp.size - s->temp.pos < 1)
 531                 return XZ_DATA_ERROR;
 532
 533         ret = xz_dec_lzma2_reset(s->lzma2, s->temp.buf[s->temp.pos++]);
 534         if (ret != XZ_OK)
 535                 return ret;
 536
 537         /* The rest must be Header Padding. */
 538         while (s->temp.pos < s->temp.size)
 539                 if (s->temp.buf[s->temp.pos++] != 0x00)
 540                         return XZ_OPTIONS_ERROR;
 541
 542         s->temp.pos = 0;
 543         s->block.compressed = 0;
 544         s->block.uncompressed = 0;
 545
 546         return XZ_OK;
 547 }
 548
 549 static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
 550 {
 551         enum xz_ret ret;
 552
 553         /*
 554          * Store the start position for the case when we are in the middle
 555          * of the Index field.
 556          */
 557         s->in_start = b->in_pos;
 558
 559         while (true) {
 560                 switch (s->sequence) {
 561                 case SEQ_STREAM_HEADER:
 562                         /*
 563                          * Stream Header is copied to s->temp, and then
 564                          * decoded from there. This way if the caller
 565                          * gives us only little input at a time, we can
 566                          * still keep the Stream Header decoding code
 567                          * simple. Similar approach is used in many places
 568                          * in this file.
 569                          */
 570                         if (!fill_temp(s, b))
 571                                 return XZ_OK;
 572
 573                         /*
 574                          * If dec_stream_header() returns
 575                          * XZ_UNSUPPORTED_CHECK, it is still possible
 576                          * to continue decoding if working in multi-call
 577                          * mode. Thus, update s->sequence before calling
 578                          * dec_stream_header().
 579                          */
 580                         s->sequence = SEQ_BLOCK_START;
 581
 582                         ret = dec_stream_header(s);
 583                         if (ret != XZ_OK)
 584                                 return ret;
 585
 586                         fallthrough;
 587
 588                 case SEQ_BLOCK_START:
 589                         /* We need one byte of input to continue. */
 590                         if (b->in_pos == b->in_size)
 591                                 return XZ_OK;
 592
 593                         /* See if this is the beginning of the Index field. */
 594                         if (b->in[b->in_pos] == 0) {
 595                                 s->in_start = b->in_pos++;
 596                                 s->sequence = SEQ_INDEX;
 597                                 break;
 598                         }
 599
 600                         /*
 601                          * Calculate the size of the Block Header and
 602                          * prepare to decode it.
 603                          */
 604                         s->block_header.size
 605                                 = ((uint32_t)b->in[b->in_pos] + 1) * 4;
 606
 607                         s->temp.size = s->block_header.size;
 608                         s->temp.pos = 0;
 609                         s->sequence = SEQ_BLOCK_HEADER;
 610
 611                         fallthrough;
 612
 613                 case SEQ_BLOCK_HEADER:
 614                         if (!fill_temp(s, b))
 615                                 return XZ_OK;
 616
 617                         ret = dec_block_header(s);
 618                         if (ret != XZ_OK)
 619                                 return ret;
 620
 621                         s->sequence = SEQ_BLOCK_UNCOMPRESS;
 622
 623                         fallthrough;
 624
 625                 case SEQ_BLOCK_UNCOMPRESS:
 626                         ret = dec_block(s, b);
 627                         if (ret != XZ_STREAM_END)
 628                                 return ret;
 629
 630                         s->sequence = SEQ_BLOCK_PADDING;
 631
 632                         fallthrough;
 633
 634                 case SEQ_BLOCK_PADDING:
 635                         /*
 636                          * Size of Compressed Data + Block Padding
 637                          * must be a multiple of four. We don't need
 638                          * s->block.compressed for anything else
 639                          * anymore, so we use it here to test the size
 640                          * of the Block Padding field.
 641                          */
 642                         while (s->block.compressed & 3) {
 643                                 if (b->in_pos == b->in_size)
 644                                         return XZ_OK;
 645
 646                                 if (b->in[b->in_pos++] != 0)
 647                                         return XZ_DATA_ERROR;
 648
 649                                 ++s->block.compressed;
 650                         }
 651
 652                         s->sequence = SEQ_BLOCK_CHECK;
 653
 654                         fallthrough;
 655
 656                 case SEQ_BLOCK_CHECK:
 657                         if (s->check_type == XZ_CHECK_CRC32) {
 658                                 ret = crc32_validate(s, b);
 659                                 if (ret != XZ_STREAM_END)
 660                                         return ret;
 661                         }
 662 #ifdef XZ_DEC_ANY_CHECK
 663                         else if (!check_skip(s, b)) {
 664                                 return XZ_OK;
 665                         }
 666 #endif
 667
 668                         s->sequence = SEQ_BLOCK_START;
 669                         break;
 670
 671                 case SEQ_INDEX:
 672                         ret = dec_index(s, b);
 673                         if (ret != XZ_STREAM_END)
 674                                 return ret;
 675
 676                         s->sequence = SEQ_INDEX_PADDING;
 677
 678                         fallthrough;
 679
 680                 case SEQ_INDEX_PADDING:
 681                         while ((s->index.size + (b->in_pos - s->in_start))
 682                                         & 3) {
 683                                 if (b->in_pos == b->in_size) {
 684                                         index_update(s, b);
 685                                         return XZ_OK;
 686                                 }
 687
 688                                 if (b->in[b->in_pos++] != 0)
 689                                         return XZ_DATA_ERROR;
 690                         }
 691
 692                         /* Finish the CRC32 value and Index size. */
 693                         index_update(s, b);
 694
 695                         /* Compare the hashes to validate the Index field. */
 696                         if (!memeq(&s->block.hash, &s->index.hash,
 697                                         sizeof(s->block.hash)))
 698                                 return XZ_DATA_ERROR;
 699
 700                         s->sequence = SEQ_INDEX_CRC32;
 701
 702                         fallthrough;
 703
 704                 case SEQ_INDEX_CRC32:
 705                         ret = crc32_validate(s, b);
 706                         if (ret != XZ_STREAM_END)
 707                                 return ret;
 708
 709                         s->temp.size = STREAM_HEADER_SIZE;
 710                         s->sequence = SEQ_STREAM_FOOTER;
 711
 712                         fallthrough;
 713
 714                 case SEQ_STREAM_FOOTER:
 715                         if (!fill_temp(s, b))
 716                                 return XZ_OK;
 717
 718                         return dec_stream_footer(s);
 719                 }
 720         }
 721
 722         /* Never reached */
 723 }
 724
 725 /*
 726  * xz_dec_run() is a wrapper for dec_main() to handle some special cases in
 727  * multi-call and single-call decoding.
 728  *
 729  * In multi-call mode, we must return XZ_BUF_ERROR when it seems clear that we
 730  * are not going to make any progress anymore. This is to prevent the caller
 731  * from calling us infinitely when the input file is truncated or otherwise
 732  * corrupt. Since zlib-style API allows that the caller fills the input buffer
 733  * only when the decoder doesn't produce any new output, we have to be careful
 734  * to avoid returning XZ_BUF_ERROR too easily: XZ_BUF_ERROR is returned only
 735  * after the second consecutive call to xz_dec_run() that makes no progress.
 736  *
 737  * In single-call mode, if we couldn't decode everything and no error
 738  * occurred, either the input is truncated or the output buffer is too small.
 739  * Since we know that the last input byte never produces any output, we know
 740  * that if all the input was consumed and decoding wasn't finished, the file
 741  * must be corrupt. Otherwise the output buffer has to be too small or the
 742  * file is corrupt in a way that decoding it produces too big output.
 743  *
 744  * If single-call decoding fails, we reset b->in_pos and b->out_pos back to
 745  * their original values. This is because with some filter chains there won't
 746  * be any valid uncompressed data in the output buffer unless the decoding
 747  * actually succeeds (that's the price to pay of using the output buffer as
 748  * the workspace).
 749  */
 750 XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b)
 751 {
 752         size_t in_start;
 753         size_t out_start;
 754         enum xz_ret ret;
 755
 756         if (DEC_IS_SINGLE(s->mode))
 757                 xz_dec_reset(s);
 758
 759         in_start = b->in_pos;
 760         out_start = b->out_pos;
 761         ret = dec_main(s, b);
 762
 763         if (DEC_IS_SINGLE(s->mode)) {
 764                 if (ret == XZ_OK)
 765                         ret = b->in_pos == b->in_size
 766                                         ? XZ_DATA_ERROR : XZ_BUF_ERROR;
 767
 768                 if (ret != XZ_STREAM_END) {
 769                         b->in_pos = in_start;
 770                         b->out_pos = out_start;
 771                 }
 772
 773         } else if (ret == XZ_OK && in_start == b->in_pos
 774                         && out_start == b->out_pos) {
 775                 if (s->allow_buf_error)
 776                         ret = XZ_BUF_ERROR;
 777
 778                 s->allow_buf_error = true;
 779         } else {
 780                 s->allow_buf_error = false;
 781         }
 782
 783         return ret;
 784 }
 785
 786 XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max)
 787 {
 788         struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
 789         if (s == NULL)
 790                 return NULL;
 791
 792         s->mode = mode;
 793
 794 #ifdef XZ_DEC_BCJ
 795         s->bcj = xz_dec_bcj_create(DEC_IS_SINGLE(mode));
 796         if (s->bcj == NULL)
 797                 goto error_bcj;
 798 #endif
 799
 800         s->lzma2 = xz_dec_lzma2_create(mode, dict_max);
 801         if (s->lzma2 == NULL)
 802                 goto error_lzma2;
 803
 804         xz_dec_reset(s);
 805         return s;
 806
 807 error_lzma2:
 808 #ifdef XZ_DEC_BCJ
 809         xz_dec_bcj_end(s->bcj);
 810 error_bcj:
 811 #endif
 812         kfree(s);
 813         return NULL;
 814 }
 815
 816 XZ_EXTERN void xz_dec_reset(struct xz_dec *s)
 817 {
 818         s->sequence = SEQ_STREAM_HEADER;
 819         s->allow_buf_error = false;
 820         s->pos = 0;
 821         s->crc32 = 0;
 822         memzero(&s->block, sizeof(s->block));
 823         memzero(&s->index, sizeof(s->index));
 824         s->temp.pos = 0;
 825         s->temp.size = STREAM_HEADER_SIZE;
 826 }
 827
 828 XZ_EXTERN void xz_dec_end(struct xz_dec *s)
 829 {
 830         if (s != NULL) {
 831                 xz_dec_lzma2_end(s->lzma2);
 832 #ifdef XZ_DEC_BCJ
 833                 xz_dec_bcj_end(s->bcj);
 834 #endif
 835                 kfree(s);
 836         }
 837 }