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TOMOYO Linux Cross Reference
Linux/lib/xz/xz_dec_stream.c

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  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                 case SEQ_BLOCK_START:
587                         /* We need one byte of input to continue. */
588                         if (b->in_pos == b->in_size)
589                                 return XZ_OK;
590 
591                         /* See if this is the beginning of the Index field. */
592                         if (b->in[b->in_pos] == 0) {
593                                 s->in_start = b->in_pos++;
594                                 s->sequence = SEQ_INDEX;
595                                 break;
596                         }
597 
598                         /*
599                          * Calculate the size of the Block Header and
600                          * prepare to decode it.
601                          */
602                         s->block_header.size
603                                 = ((uint32_t)b->in[b->in_pos] + 1) * 4;
604 
605                         s->temp.size = s->block_header.size;
606                         s->temp.pos = 0;
607                         s->sequence = SEQ_BLOCK_HEADER;
608 
609                 case SEQ_BLOCK_HEADER:
610                         if (!fill_temp(s, b))
611                                 return XZ_OK;
612 
613                         ret = dec_block_header(s);
614                         if (ret != XZ_OK)
615                                 return ret;
616 
617                         s->sequence = SEQ_BLOCK_UNCOMPRESS;
618 
619                 case SEQ_BLOCK_UNCOMPRESS:
620                         ret = dec_block(s, b);
621                         if (ret != XZ_STREAM_END)
622                                 return ret;
623 
624                         s->sequence = SEQ_BLOCK_PADDING;
625 
626                 case SEQ_BLOCK_PADDING:
627                         /*
628                          * Size of Compressed Data + Block Padding
629                          * must be a multiple of four. We don't need
630                          * s->block.compressed for anything else
631                          * anymore, so we use it here to test the size
632                          * of the Block Padding field.
633                          */
634                         while (s->block.compressed & 3) {
635                                 if (b->in_pos == b->in_size)
636                                         return XZ_OK;
637 
638                                 if (b->in[b->in_pos++] != 0)
639                                         return XZ_DATA_ERROR;
640 
641                                 ++s->block.compressed;
642                         }
643 
644                         s->sequence = SEQ_BLOCK_CHECK;
645 
646                 case SEQ_BLOCK_CHECK:
647                         if (s->check_type == XZ_CHECK_CRC32) {
648                                 ret = crc32_validate(s, b);
649                                 if (ret != XZ_STREAM_END)
650                                         return ret;
651                         }
652 #ifdef XZ_DEC_ANY_CHECK
653                         else if (!check_skip(s, b)) {
654                                 return XZ_OK;
655                         }
656 #endif
657 
658                         s->sequence = SEQ_BLOCK_START;
659                         break;
660 
661                 case SEQ_INDEX:
662                         ret = dec_index(s, b);
663                         if (ret != XZ_STREAM_END)
664                                 return ret;
665 
666                         s->sequence = SEQ_INDEX_PADDING;
667 
668                 case SEQ_INDEX_PADDING:
669                         while ((s->index.size + (b->in_pos - s->in_start))
670                                         & 3) {
671                                 if (b->in_pos == b->in_size) {
672                                         index_update(s, b);
673                                         return XZ_OK;
674                                 }
675 
676                                 if (b->in[b->in_pos++] != 0)
677                                         return XZ_DATA_ERROR;
678                         }
679 
680                         /* Finish the CRC32 value and Index size. */
681                         index_update(s, b);
682 
683                         /* Compare the hashes to validate the Index field. */
684                         if (!memeq(&s->block.hash, &s->index.hash,
685                                         sizeof(s->block.hash)))
686                                 return XZ_DATA_ERROR;
687 
688                         s->sequence = SEQ_INDEX_CRC32;
689 
690                 case SEQ_INDEX_CRC32:
691                         ret = crc32_validate(s, b);
692                         if (ret != XZ_STREAM_END)
693                                 return ret;
694 
695                         s->temp.size = STREAM_HEADER_SIZE;
696                         s->sequence = SEQ_STREAM_FOOTER;
697 
698                 case SEQ_STREAM_FOOTER:
699                         if (!fill_temp(s, b))
700                                 return XZ_OK;
701 
702                         return dec_stream_footer(s);
703                 }
704         }
705 
706         /* Never reached */
707 }
708 
709 /*
710  * xz_dec_run() is a wrapper for dec_main() to handle some special cases in
711  * multi-call and single-call decoding.
712  *
713  * In multi-call mode, we must return XZ_BUF_ERROR when it seems clear that we
714  * are not going to make any progress anymore. This is to prevent the caller
715  * from calling us infinitely when the input file is truncated or otherwise
716  * corrupt. Since zlib-style API allows that the caller fills the input buffer
717  * only when the decoder doesn't produce any new output, we have to be careful
718  * to avoid returning XZ_BUF_ERROR too easily: XZ_BUF_ERROR is returned only
719  * after the second consecutive call to xz_dec_run() that makes no progress.
720  *
721  * In single-call mode, if we couldn't decode everything and no error
722  * occurred, either the input is truncated or the output buffer is too small.
723  * Since we know that the last input byte never produces any output, we know
724  * that if all the input was consumed and decoding wasn't finished, the file
725  * must be corrupt. Otherwise the output buffer has to be too small or the
726  * file is corrupt in a way that decoding it produces too big output.
727  *
728  * If single-call decoding fails, we reset b->in_pos and b->out_pos back to
729  * their original values. This is because with some filter chains there won't
730  * be any valid uncompressed data in the output buffer unless the decoding
731  * actually succeeds (that's the price to pay of using the output buffer as
732  * the workspace).
733  */
734 XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b)
735 {
736         size_t in_start;
737         size_t out_start;
738         enum xz_ret ret;
739 
740         if (DEC_IS_SINGLE(s->mode))
741                 xz_dec_reset(s);
742 
743         in_start = b->in_pos;
744         out_start = b->out_pos;
745         ret = dec_main(s, b);
746 
747         if (DEC_IS_SINGLE(s->mode)) {
748                 if (ret == XZ_OK)
749                         ret = b->in_pos == b->in_size
750                                         ? XZ_DATA_ERROR : XZ_BUF_ERROR;
751 
752                 if (ret != XZ_STREAM_END) {
753                         b->in_pos = in_start;
754                         b->out_pos = out_start;
755                 }
756 
757         } else if (ret == XZ_OK && in_start == b->in_pos
758                         && out_start == b->out_pos) {
759                 if (s->allow_buf_error)
760                         ret = XZ_BUF_ERROR;
761 
762                 s->allow_buf_error = true;
763         } else {
764                 s->allow_buf_error = false;
765         }
766 
767         return ret;
768 }
769 
770 XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max)
771 {
772         struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
773         if (s == NULL)
774                 return NULL;
775 
776         s->mode = mode;
777 
778 #ifdef XZ_DEC_BCJ
779         s->bcj = xz_dec_bcj_create(DEC_IS_SINGLE(mode));
780         if (s->bcj == NULL)
781                 goto error_bcj;
782 #endif
783 
784         s->lzma2 = xz_dec_lzma2_create(mode, dict_max);
785         if (s->lzma2 == NULL)
786                 goto error_lzma2;
787 
788         xz_dec_reset(s);
789         return s;
790 
791 error_lzma2:
792 #ifdef XZ_DEC_BCJ
793         xz_dec_bcj_end(s->bcj);
794 error_bcj:
795 #endif
796         kfree(s);
797         return NULL;
798 }
799 
800 XZ_EXTERN void xz_dec_reset(struct xz_dec *s)
801 {
802         s->sequence = SEQ_STREAM_HEADER;
803         s->allow_buf_error = false;
804         s->pos = 0;
805         s->crc32 = 0;
806         memzero(&s->block, sizeof(s->block));
807         memzero(&s->index, sizeof(s->index));
808         s->temp.pos = 0;
809         s->temp.size = STREAM_HEADER_SIZE;
810 }
811 
812 XZ_EXTERN void xz_dec_end(struct xz_dec *s)
813 {
814         if (s != NULL) {
815                 xz_dec_lzma2_end(s->lzma2);
816 #ifdef XZ_DEC_BCJ
817                 xz_dec_bcj_end(s->bcj);
818 #endif
819                 kfree(s);
820         }
821 }
822 

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