xz_dec_stream.c

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