summaryrefslogtreecommitdiff
path: root/lib/xz/xz_dec_stream.c
blob: 32ab2a08b7cbc9ff5a874d1ffe5cfd12d221e901 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
/*
 * .xz Stream decoder
 *
 * Author: Lasse Collin <lasse.collin@tukaani.org>
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */

#include "xz_private.h"
#include "xz_stream.h"

/* Hash used to validate the Index field */
struct xz_dec_hash {
	vli_type unpadded;
	vli_type uncompressed;
	uint32_t crc32;
};

struct xz_dec {
	/* Position in dec_main() */
	enum {
		SEQ_STREAM_HEADER,
		SEQ_BLOCK_START,
		SEQ_BLOCK_HEADER,
		SEQ_BLOCK_UNCOMPRESS,
		SEQ_BLOCK_PADDING,
		SEQ_BLOCK_CHECK,
		SEQ_INDEX,
		SEQ_INDEX_PADDING,
		SEQ_INDEX_CRC32,
		SEQ_STREAM_FOOTER
	} sequence;

	/* Position in variable-length integers and Check fields */
	uint32_t pos;

	/* Variable-length integer decoded by dec_vli() */
	vli_type vli;

	/* Saved in_pos and out_pos */
	size_t in_start;
	size_t out_start;

	/* CRC32 value in Block or Index */
	uint32_t crc32;

	/* Type of the integrity check calculated from uncompressed data */
	enum xz_check check_type;

	/* Operation mode */
	enum xz_mode mode;

	/*
	 * True if the next call to xz_dec_run() is allowed to return
	 * XZ_BUF_ERROR.
	 */
	bool allow_buf_error;

	/* Information stored in Block Header */
	struct {
		/*
		 * Value stored in the Compressed Size field, or
		 * VLI_UNKNOWN if Compressed Size is not present.
		 */
		vli_type compressed;

		/*
		 * Value stored in the Uncompressed Size field, or
		 * VLI_UNKNOWN if Uncompressed Size is not present.
		 */
		vli_type uncompressed;

		/* Size of the Block Header field */
		uint32_t size;
	} block_header;

	/* Information collected when decoding Blocks */
	struct {
		/* Observed compressed size of the current Block */
		vli_type compressed;

		/* Observed uncompressed size of the current Block */
		vli_type uncompressed;

		/* Number of Blocks decoded so far */
		vli_type count;

		/*
		 * Hash calculated from the Block sizes. This is used to
		 * validate the Index field.
		 */
		struct xz_dec_hash hash;
	} block;

	/* Variables needed when verifying the Index field */
	struct {
		/* Position in dec_index() */
		enum {
			SEQ_INDEX_COUNT,
			SEQ_INDEX_UNPADDED,
			SEQ_INDEX_UNCOMPRESSED
		} sequence;

		/* Size of the Index in bytes */
		vli_type size;

		/* Number of Records (matches block.count in valid files) */
		vli_type count;

		/*
		 * Hash calculated from the Records (matches block.hash in
		 * valid files).
		 */
		struct xz_dec_hash hash;
	} index;

	/*
	 * Temporary buffer needed to hold Stream Header, Block Header,
	 * and Stream Footer. The Block Header is the biggest (1 KiB)
	 * so we reserve space according to that. buf[] has to be aligned
	 * to a multiple of four bytes; the size_t variables before it
	 * should guarantee this.
	 */
	struct {
		size_t pos;
		size_t size;
		uint8_t buf[1024];
	} temp;

	struct xz_dec_lzma2 *lzma2;

#ifdef XZ_DEC_BCJ
	struct xz_dec_bcj *bcj;
	bool bcj_active;
#endif
};

#ifdef XZ_DEC_ANY_CHECK
/* Sizes of the Check field with different Check IDs */
static const uint8_t check_sizes[16] = {
	0,
	4, 4, 4,
	8, 8, 8,
	16, 16, 16,
	32, 32, 32,
	64, 64, 64
};
#endif

/*
 * Fill s->temp by copying data starting from b->in[b->in_pos]. Caller
 * must have set s->temp.pos to indicate how much data we are supposed
 * to copy into s->temp.buf. Return true once s->temp.pos has reached
 * s->temp.size.
 */
static bool fill_temp(struct xz_dec *s, struct xz_buf *b)
{
	size_t copy_size = min_t(size_t,
			b->in_size - b->in_pos, s->temp.size - s->temp.pos);

	memcpy(s->temp.buf + s->temp.pos, b->in + b->in_pos, copy_size);
	b->in_pos += copy_size;
	s->temp.pos += copy_size;

	if (s->temp.pos == s->temp.size) {
		s->temp.pos = 0;
		return true;
	}

	return false;
}

/* Decode a variable-length integer (little-endian base-128 encoding) */
static enum xz_ret dec_vli(struct xz_dec *s, const uint8_t *in,
			   size_t *in_pos, size_t in_size)
{
	uint8_t byte;

	if (s->pos == 0)
		s->vli = 0;

	while (*in_pos < in_size) {
		byte = in[*in_pos];
		++*in_pos;

		s->vli |= (vli_type)(byte & 0x7F) << s->pos;

		if ((byte & 0x80) == 0) {
			/* Don't allow non-minimal encodings. */
			if (byte == 0 && s->pos != 0)
				return XZ_DATA_ERROR;

			s->pos = 0;
			return XZ_STREAM_END;
		}

		s->pos += 7;
		if (s->pos == 7 * VLI_BYTES_MAX)
			return XZ_DATA_ERROR;
	}

	return XZ_OK;
}

/*
 * Decode the Compressed Data field from a Block. Update and validate
 * the observed compressed and uncompressed sizes of the Block so that
 * they don't exceed the values possibly stored in the Block Header
 * (validation assumes that no integer overflow occurs, since vli_type
 * is normally uint64_t). Update the CRC32 if presence of the CRC32
 * field was indicated in Stream Header.
 *
 * Once the decoding is finished, validate that the observed sizes match
 * the sizes possibly stored in the Block Header. Update the hash and
 * Block count, which are later used to validate the Index field.
 */
static enum xz_ret dec_block(struct xz_dec *s, struct xz_buf *b)
{
	enum xz_ret ret;

	s->in_start = b->in_pos;
	s->out_start = b->out_pos;

#ifdef XZ_DEC_BCJ
	if (s->bcj_active)
		ret = xz_dec_bcj_run(s->bcj, s->lzma2, b);
	else
#endif
		ret = xz_dec_lzma2_run(s->lzma2, b);

	s->block.compressed += b->in_pos - s->in_start;
	s->block.uncompressed += b->out_pos - s->out_start;

	/*
	 * There is no need to separately check for VLI_UNKNOWN, since
	 * the observed sizes are always smaller than VLI_UNKNOWN.
	 */
	if (s->block.compressed > s->block_header.compressed
			|| s->block.uncompressed
				> s->block_header.uncompressed)
		return XZ_DATA_ERROR;

	if (s->check_type == XZ_CHECK_CRC32)
		s->crc32 = xz_crc32(b->out + s->out_start,
				b->out_pos - s->out_start, s->crc32);

	if (ret == XZ_STREAM_END) {
		if (s->block_header.compressed != VLI_UNKNOWN
				&& s->block_header.compressed
					!= s->block.compressed)
			return XZ_DATA_ERROR;

		if (s->block_header.uncompressed != VLI_UNKNOWN
				&& s->block_header.uncompressed
					!= s->block.uncompressed)
			return XZ_DATA_ERROR;

		s->block.hash.unpadded += s->block_header.size
				+ s->block.compressed;

#ifdef XZ_DEC_ANY_CHECK
		s->block.hash.unpadded += check_sizes[s->check_type];
#else
		if (s->check_type == XZ_CHECK_CRC32)
			s->block.hash.unpadded += 4;
#endif

		s->block.hash.uncompressed += s->block.uncompressed;
		s->block.hash.crc32 = xz_crc32(
				(const uint8_t *)&s->block.hash,
				sizeof(s->block.hash), s->block.hash.crc32);

		++s->block.count;
	}

	return ret;
}

/* Update the Index size and the CRC32 value. */
static void index_update(struct xz_dec *s, const struct xz_buf *b)
{
	size_t in_used = b->in_pos - s->in_start;
	s->index.size += in_used;
	s->crc32 = xz_crc32(b->in + s->in_start, in_used, s->crc32);
}

/*
 * Decode the Number of Records, Unpadded Size, and Uncompressed Size
 * fields from the Index field. That is, Index Padding and CRC32 are not
 * decoded by this function.
 *
 * This can return XZ_OK (more input needed), XZ_STREAM_END (everything
 * successfully decoded), or XZ_DATA_ERROR (input is corrupt).
 */
static enum xz_ret dec_index(struct xz_dec *s, struct xz_buf *b)
{
	enum xz_ret ret;

	do {
		ret = dec_vli(s, b->in, &b->in_pos, b->in_size);
		if (ret != XZ_STREAM_END) {
			index_update(s, b);
			return ret;
		}

		switch (s->index.sequence) {
		case SEQ_INDEX_COUNT:
			s->index.count = s->vli;

			/*
			 * Validate that the Number of Records field
			 * indicates the same number of Records as
			 * there were Blocks in the Stream.
			 */
			if (s->index.count != s->block.count)
				return XZ_DATA_ERROR;

			s->index.sequence = SEQ_INDEX_UNPADDED;
			break;

		case SEQ_INDEX_UNPADDED:
			s->index.hash.unpadded += s->vli;
			s->index.sequence = SEQ_INDEX_UNCOMPRESSED;
			break;

		case SEQ_INDEX_UNCOMPRESSED:
			s->index.hash.uncompressed += s->vli;
			s->index.hash.crc32 = xz_crc32(
					(const uint8_t *)&s->index.hash,
					sizeof(s->index.hash),
					s->index.hash.crc32);
			--s->index.count;
			s->index.sequence = SEQ_INDEX_UNPADDED;
			break;
		}
	} while (s->index.count > 0);

	return XZ_STREAM_END;
}

/*
 * Validate that the next four input bytes match the value of s->crc32.
 * s->pos must be zero when starting to validate the first byte.
 */
static enum xz_ret crc32_validate(struct xz_dec *s, struct xz_buf *b)
{
	do {
		if (b->in_pos == b->in_size)
			return XZ_OK;

		if (((s->crc32 >> s->pos) & 0xFF) != b->in[b->in_pos++])
			return XZ_DATA_ERROR;

		s->pos += 8;

	} while (s->pos < 32);

	s->crc32 = 0;
	s->pos = 0;

	return XZ_STREAM_END;
}

#ifdef XZ_DEC_ANY_CHECK
/*
 * Skip over the Check field when the Check ID is not supported.
 * Returns true once the whole Check field has been skipped over.
 */
static bool check_skip(struct xz_dec *s, struct xz_buf *b)
{
	while (s->pos < check_sizes[s->check_type]) {
		if (b->in_pos == b->in_size)
			return false;

		++b->in_pos;
		++s->pos;
	}

	s->pos = 0;

	return true;
}
#endif

/* Decode the Stream Header field (the first 12 bytes of the .xz Stream). */
static enum xz_ret dec_stream_header(struct xz_dec *s)
{
	if (!memeq(s->temp.buf, HEADER_MAGIC, HEADER_MAGIC_SIZE))
		return XZ_FORMAT_ERROR;

	if (xz_crc32(s->temp.buf + HEADER_MAGIC_SIZE, 2, 0)
			!= get_le32(s->temp.buf + HEADER_MAGIC_SIZE + 2))
		return XZ_DATA_ERROR;

	if (s->temp.buf[HEADER_MAGIC_SIZE] != 0)
		return XZ_OPTIONS_ERROR;

	/*
	 * Of integrity checks, we support only none (Check ID = 0) and
	 * CRC32 (Check ID = 1). However, if XZ_DEC_ANY_CHECK is defined,
	 * we will accept other check types too, but then the check won't
	 * be verified and a warning (XZ_UNSUPPORTED_CHECK) will be given.
	 */
	s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];

#ifdef XZ_DEC_ANY_CHECK
	if (s->check_type > XZ_CHECK_MAX)
		return XZ_OPTIONS_ERROR;

	if (s->check_type > XZ_CHECK_CRC32)
		return XZ_UNSUPPORTED_CHECK;
#else
	if (s->check_type > XZ_CHECK_CRC32)
		return XZ_OPTIONS_ERROR;
#endif

	return XZ_OK;
}

/* Decode the Stream Footer field (the last 12 bytes of the .xz Stream) */
static enum xz_ret dec_stream_footer(struct xz_dec *s)
{
	if (!memeq(s->temp.buf + 10, FOOTER_MAGIC, FOOTER_MAGIC_SIZE))
		return XZ_DATA_ERROR;

	if (xz_crc32(s->temp.buf + 4, 6, 0) != get_le32(s->temp.buf))
		return XZ_DATA_ERROR;

	/*
	 * Validate Backward Size. Note that we never added the size of the
	 * Index CRC32 field to s->index.size, thus we use s->index.size / 4
	 * instead of s->index.size / 4 - 1.
	 */
	if ((s->index.size >> 2) != get_le32(s->temp.buf + 4))
		return XZ_DATA_ERROR;

	if (s->temp.buf[8] != 0 || s->temp.buf[9] != s->check_type)
		return XZ_DATA_ERROR;

	/*
	 * Use XZ_STREAM_END instead of XZ_OK to be more convenient
	 * for the caller.
	 */
	return XZ_STREAM_END;
}

/* Decode the Block Header and initialize the filter chain. */
static enum xz_ret dec_block_header(struct xz_dec *s)
{
	enum xz_ret ret;

	/*
	 * Validate the CRC32. We know that the temp buffer is at least
	 * eight bytes so this is safe.
	 */
	s->temp.size -= 4;
	if (xz_crc32(s->temp.buf, s->temp.size, 0)
			!= get_le32(s->temp.buf + s->temp.size))
		return XZ_DATA_ERROR;

	s->temp.pos = 2;

	/*
	 * Catch unsupported Block Flags. We support only one or two filters
	 * in the chain, so we catch that with the same test.
	 */
#ifdef XZ_DEC_BCJ
	if (s->temp.buf[1] & 0x3E)
#else
	if (s->temp.buf[1] & 0x3F)
#endif
		return XZ_OPTIONS_ERROR;

	/* Compressed Size */
	if (s->temp.buf[1] & 0x40) {
		if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
					!= XZ_STREAM_END)
			return XZ_DATA_ERROR;

		s->block_header.compressed = s->vli;
	} else {
		s->block_header.compressed = VLI_UNKNOWN;
	}

	/* Uncompressed Size */
	if (s->temp.buf[1] & 0x80) {
		if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
				!= XZ_STREAM_END)
			return XZ_DATA_ERROR;

		s->block_header.uncompressed = s->vli;
	} else {
		s->block_header.uncompressed = VLI_UNKNOWN;
	}

#ifdef XZ_DEC_BCJ
	/* If there are two filters, the first one must be a BCJ filter. */
	s->bcj_active = s->temp.buf[1] & 0x01;
	if (s->bcj_active) {
		if (s->temp.size - s->temp.pos < 2)
			return XZ_OPTIONS_ERROR;

		ret = xz_dec_bcj_reset(s->bcj, s->temp.buf[s->temp.pos++]);
		if (ret != XZ_OK)
			return ret;

		/*
		 * We don't support custom start offset,
		 * so Size of Properties must be zero.
		 */
		if (s->temp.buf[s->temp.pos++] != 0x00)
			return XZ_OPTIONS_ERROR;
	}
#endif

	/* Valid Filter Flags always take at least two bytes. */
	if (s->temp.size - s->temp.pos < 2)
		return XZ_DATA_ERROR;

	/* Filter ID = LZMA2 */
	if (s->temp.buf[s->temp.pos++] != 0x21)
		return XZ_OPTIONS_ERROR;

	/* Size of Properties = 1-byte Filter Properties */
	if (s->temp.buf[s->temp.pos++] != 0x01)
		return XZ_OPTIONS_ERROR;

	/* Filter Properties contains LZMA2 dictionary size. */
	if (s->temp.size - s->temp.pos < 1)
		return XZ_DATA_ERROR;

	ret = xz_dec_lzma2_reset(s->lzma2, s->temp.buf[s->temp.pos++]);
	if (ret != XZ_OK)
		return ret;

	/* The rest must be Header Padding. */
	while (s->temp.pos < s->temp.size)
		if (s->temp.buf[s->temp.pos++] != 0x00)
			return XZ_OPTIONS_ERROR;

	s->temp.pos = 0;
	s->block.compressed = 0;
	s->block.uncompressed = 0;

	return XZ_OK;
}

static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
{
	enum xz_ret ret;

	/*
	 * Store the start position for the case when we are in the middle
	 * of the Index field.
	 */
	s->in_start = b->in_pos;

	while (true) {
		switch (s->sequence) {
		case SEQ_STREAM_HEADER:
			/*
			 * Stream Header is copied to s->temp, and then
			 * decoded from there. This way if the caller
			 * gives us only little input at a time, we can
			 * still keep the Stream Header decoding code
			 * simple. Similar approach is used in many places
			 * in this file.
			 */
			if (!fill_temp(s, b))
				return XZ_OK;

			/*
			 * If dec_stream_header() returns
			 * XZ_UNSUPPORTED_CHECK, it is still possible
			 * to continue decoding if working in multi-call
			 * mode. Thus, update s->sequence before calling
			 * dec_stream_header().
			 */
			s->sequence = SEQ_BLOCK_START;

			ret = dec_stream_header(s);
			if (ret != XZ_OK)
				return ret;

			/* fall through */

		case SEQ_BLOCK_START:
			/* We need one byte of input to continue. */
			if (b->in_pos == b->in_size)
				return XZ_OK;

			/* See if this is the beginning of the Index field. */
			if (b->in[b->in_pos] == 0) {
				s->in_start = b->in_pos++;
				s->sequence = SEQ_INDEX;
				break;
			}

			/*
			 * Calculate the size of the Block Header and
			 * prepare to decode it.
			 */
			s->block_header.size
				= ((uint32_t)b->in[b->in_pos] + 1) * 4;

			s->temp.size = s->block_header.size;
			s->temp.pos = 0;
			s->sequence = SEQ_BLOCK_HEADER;

			/* fall through */

		case SEQ_BLOCK_HEADER:
			if (!fill_temp(s, b))
				return XZ_OK;

			ret = dec_block_header(s);
			if (ret != XZ_OK)
				return ret;

			s->sequence = SEQ_BLOCK_UNCOMPRESS;

			/* fall through */

		case SEQ_BLOCK_UNCOMPRESS:
			ret = dec_block(s, b);
			if (ret != XZ_STREAM_END)
				return ret;

			s->sequence = SEQ_BLOCK_PADDING;

			/* fall through */

		case SEQ_BLOCK_PADDING:
			/*
			 * Size of Compressed Data + Block Padding
			 * must be a multiple of four. We don't need
			 * s->block.compressed for anything else
			 * anymore, so we use it here to test the size
			 * of the Block Padding field.
			 */
			while (s->block.compressed & 3) {
				if (b->in_pos == b->in_size)
					return XZ_OK;

				if (b->in[b->in_pos++] != 0)
					return XZ_DATA_ERROR;

				++s->block.compressed;
			}

			s->sequence = SEQ_BLOCK_CHECK;

			/* fall through */

		case SEQ_BLOCK_CHECK:
			if (s->check_type == XZ_CHECK_CRC32) {
				ret = crc32_validate(s, b);
				if (ret != XZ_STREAM_END)
					return ret;
			}
#ifdef XZ_DEC_ANY_CHECK
			else if (!check_skip(s, b)) {
				return XZ_OK;
			}
#endif

			s->sequence = SEQ_BLOCK_START;
			break;

		case SEQ_INDEX:
			ret = dec_index(s, b);
			if (ret != XZ_STREAM_END)
				return ret;

			s->sequence = SEQ_INDEX_PADDING;

			/* fall through */

		case SEQ_INDEX_PADDING:
			while ((s->index.size + (b->in_pos - s->in_start))
					& 3) {
				if (b->in_pos == b->in_size) {
					index_update(s, b);
					return XZ_OK;
				}

				if (b->in[b->in_pos++] != 0)
					return XZ_DATA_ERROR;
			}

			/* Finish the CRC32 value and Index size. */
			index_update(s, b);

			/* Compare the hashes to validate the Index field. */
			if (!memeq(&s->block.hash, &s->index.hash,
					sizeof(s->block.hash)))
				return XZ_DATA_ERROR;

			s->sequence = SEQ_INDEX_CRC32;

			/* fall through */

		case SEQ_INDEX_CRC32:
			ret = crc32_validate(s, b);
			if (ret != XZ_STREAM_END)
				return ret;

			s->temp.size = STREAM_HEADER_SIZE;
			s->sequence = SEQ_STREAM_FOOTER;

			/* fall through */

		case SEQ_STREAM_FOOTER:
			if (!fill_temp(s, b))
				return XZ_OK;

			return dec_stream_footer(s);
		}
	}

	/* Never reached */
}

/*
 * xz_dec_run() is a wrapper for dec_main() to handle some special cases in
 * multi-call and single-call decoding.
 *
 * In multi-call mode, we must return XZ_BUF_ERROR when it seems clear that we
 * are not going to make any progress anymore. This is to prevent the caller
 * from calling us infinitely when the input file is truncated or otherwise
 * corrupt. Since zlib-style API allows that the caller fills the input buffer
 * only when the decoder doesn't produce any new output, we have to be careful
 * to avoid returning XZ_BUF_ERROR too easily: XZ_BUF_ERROR is returned only
 * after the second consecutive call to xz_dec_run() that makes no progress.
 *
 * In single-call mode, if we couldn't decode everything and no error
 * occurred, either the input is truncated or the output buffer is too small.
 * Since we know that the last input byte never produces any output, we know
 * that if all the input was consumed and decoding wasn't finished, the file
 * must be corrupt. Otherwise the output buffer has to be too small or the
 * file is corrupt in a way that decoding it produces too big output.
 *
 * If single-call decoding fails, we reset b->in_pos and b->out_pos back to
 * their original values. This is because with some filter chains there won't
 * be any valid uncompressed data in the output buffer unless the decoding
 * actually succeeds (that's the price to pay of using the output buffer as
 * the workspace).
 */
XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b)
{
	size_t in_start;
	size_t out_start;
	enum xz_ret ret;

	if (DEC_IS_SINGLE(s->mode))
		xz_dec_reset(s);

	in_start = b->in_pos;
	out_start = b->out_pos;
	ret = dec_main(s, b);

	if (DEC_IS_SINGLE(s->mode)) {
		if (ret == XZ_OK)
			ret = b->in_pos == b->in_size
					? XZ_DATA_ERROR : XZ_BUF_ERROR;

		if (ret != XZ_STREAM_END) {
			b->in_pos = in_start;
			b->out_pos = out_start;
		}

	} else if (ret == XZ_OK && in_start == b->in_pos
			&& out_start == b->out_pos) {
		if (s->allow_buf_error)
			ret = XZ_BUF_ERROR;

		s->allow_buf_error = true;
	} else {
		s->allow_buf_error = false;
	}

	return ret;
}

XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max)
{
	struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
	if (s == NULL)
		return NULL;

	s->mode = mode;

#ifdef XZ_DEC_BCJ
	s->bcj = xz_dec_bcj_create(DEC_IS_SINGLE(mode));
	if (s->bcj == NULL)
		goto error_bcj;
#endif

	s->lzma2 = xz_dec_lzma2_create(mode, dict_max);
	if (s->lzma2 == NULL)
		goto error_lzma2;

	xz_dec_reset(s);
	return s;

error_lzma2:
#ifdef XZ_DEC_BCJ
	xz_dec_bcj_end(s->bcj);
error_bcj:
#endif
	kfree(s);
	return NULL;
}

XZ_EXTERN void xz_dec_reset(struct xz_dec *s)
{
	s->sequence = SEQ_STREAM_HEADER;
	s->allow_buf_error = false;
	s->pos = 0;
	s->crc32 = 0;
	memzero(&s->block, sizeof(s->block));
	memzero(&s->index, sizeof(s->index));
	s->temp.pos = 0;
	s->temp.size = STREAM_HEADER_SIZE;
}

XZ_EXTERN void xz_dec_end(struct xz_dec *s)
{
	if (s != NULL) {
		xz_dec_lzma2_end(s->lzma2);
#ifdef XZ_DEC_BCJ
		xz_dec_bcj_end(s->bcj);
#endif
		kfree(s);
	}
}