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1 ///////////////////////////////////////////////////////////////////////////////
2 //
3 /// \file       index_decoder.c
4 /// \brief      Decodes the Index field
5 //
6 //  Author:     Lasse Collin
7 //
8 //  This file has been put into the public domain.
9 //  You can do whatever you want with this file.
10 //
11 ///////////////////////////////////////////////////////////////////////////////
12
13 #include "index.h"
14 #include "check.h"
15
16
17 typedef struct {
18         enum {
19                 SEQ_INDICATOR,
20                 SEQ_COUNT,
21                 SEQ_MEMUSAGE,
22                 SEQ_UNPADDED,
23                 SEQ_UNCOMPRESSED,
24                 SEQ_PADDING_INIT,
25                 SEQ_PADDING,
26                 SEQ_CRC32,
27         } sequence;
28
29         /// Memory usage limit
30         uint64_t memlimit;
31
32         /// Target Index
33         lzma_index *index;
34
35         /// Pointer give by the application, which is set after
36         /// successful decoding.
37         lzma_index **index_ptr;
38
39         /// Number of Records left to decode.
40         lzma_vli count;
41
42         /// The most recent Unpadded Size field
43         lzma_vli unpadded_size;
44
45         /// The most recent Uncompressed Size field
46         lzma_vli uncompressed_size;
47
48         /// Position in integers
49         size_t pos;
50
51         /// CRC32 of the List of Records field
52         uint32_t crc32;
53 } lzma_index_coder;
54
55
56 static lzma_ret
57 index_decode(void *coder_ptr, const lzma_allocator *allocator,
58                 const uint8_t *restrict in, size_t *restrict in_pos,
59                 size_t in_size,
60                 uint8_t *restrict out lzma_attribute((__unused__)),
61                 size_t *restrict out_pos lzma_attribute((__unused__)),
62                 size_t out_size lzma_attribute((__unused__)),
63                 lzma_action action lzma_attribute((__unused__)))
64 {
65         lzma_index_coder *coder = coder_ptr;
66
67         // Similar optimization as in index_encoder.c
68         const size_t in_start = *in_pos;
69         lzma_ret ret = LZMA_OK;
70
71         while (*in_pos < in_size)
72         switch (coder->sequence) {
73         case SEQ_INDICATOR:
74                 // Return LZMA_DATA_ERROR instead of e.g. LZMA_PROG_ERROR or
75                 // LZMA_FORMAT_ERROR, because a typical usage case for Index
76                 // decoder is when parsing the Stream backwards. If seeking
77                 // backward from the Stream Footer gives us something that
78                 // doesn't begin with Index Indicator, the file is considered
79                 // corrupt, not "programming error" or "unrecognized file
80                 // format". One could argue that the application should
81                 // verify the Index Indicator before trying to decode the
82                 // Index, but well, I suppose it is simpler this way.
83                 if (in[(*in_pos)++] != 0x00)
84                         return LZMA_DATA_ERROR;
85
86                 coder->sequence = SEQ_COUNT;
87                 break;
88
89         case SEQ_COUNT:
90                 ret = lzma_vli_decode(&coder->count, &coder->pos,
91                                 in, in_pos, in_size);
92                 if (ret != LZMA_STREAM_END)
93                         goto out;
94
95                 coder->pos = 0;
96                 coder->sequence = SEQ_MEMUSAGE;
97
98         // Fall through
99
100         case SEQ_MEMUSAGE:
101                 if (lzma_index_memusage(1, coder->count) > coder->memlimit) {
102                         ret = LZMA_MEMLIMIT_ERROR;
103                         goto out;
104                 }
105
106                 // Tell the Index handling code how many Records this
107                 // Index has to allow it to allocate memory more efficiently.
108                 lzma_index_prealloc(coder->index, coder->count);
109
110                 ret = LZMA_OK;
111                 coder->sequence = coder->count == 0
112                                 ? SEQ_PADDING_INIT : SEQ_UNPADDED;
113                 break;
114
115         case SEQ_UNPADDED:
116         case SEQ_UNCOMPRESSED: {
117                 lzma_vli *size = coder->sequence == SEQ_UNPADDED
118                                 ? &coder->unpadded_size
119                                 : &coder->uncompressed_size;
120
121                 ret = lzma_vli_decode(size, &coder->pos,
122                                 in, in_pos, in_size);
123                 if (ret != LZMA_STREAM_END)
124                         goto out;
125
126                 ret = LZMA_OK;
127                 coder->pos = 0;
128
129                 if (coder->sequence == SEQ_UNPADDED) {
130                         // Validate that encoded Unpadded Size isn't too small
131                         // or too big.
132                         if (coder->unpadded_size < UNPADDED_SIZE_MIN
133                                         || coder->unpadded_size
134                                                 > UNPADDED_SIZE_MAX)
135                                 return LZMA_DATA_ERROR;
136
137                         coder->sequence = SEQ_UNCOMPRESSED;
138                 } else {
139                         // Add the decoded Record to the Index.
140                         return_if_error(lzma_index_append(
141                                         coder->index, allocator,
142                                         coder->unpadded_size,
143                                         coder->uncompressed_size));
144
145                         // Check if this was the last Record.
146                         coder->sequence = --coder->count == 0
147                                         ? SEQ_PADDING_INIT
148                                         : SEQ_UNPADDED;
149                 }
150
151                 break;
152         }
153
154         case SEQ_PADDING_INIT:
155                 coder->pos = lzma_index_padding_size(coder->index);
156                 coder->sequence = SEQ_PADDING;
157
158         // Fall through
159
160         case SEQ_PADDING:
161                 if (coder->pos > 0) {
162                         --coder->pos;
163                         if (in[(*in_pos)++] != 0x00)
164                                 return LZMA_DATA_ERROR;
165
166                         break;
167                 }
168
169                 // Finish the CRC32 calculation.
170                 coder->crc32 = lzma_crc32(in + in_start,
171                                 *in_pos - in_start, coder->crc32);
172
173                 coder->sequence = SEQ_CRC32;
174
175         // Fall through
176
177         case SEQ_CRC32:
178                 do {
179                         if (*in_pos == in_size)
180                                 return LZMA_OK;
181
182                         if (((coder->crc32 >> (coder->pos * 8)) & 0xFF)
183                                         != in[(*in_pos)++])
184                                 return LZMA_DATA_ERROR;
185
186                 } while (++coder->pos < 4);
187
188                 // Decoding was successful, now we can let the application
189                 // see the decoded Index.
190                 *coder->index_ptr = coder->index;
191
192                 // Make index NULL so we don't free it unintentionally.
193                 coder->index = NULL;
194
195                 return LZMA_STREAM_END;
196
197         default:
198                 assert(0);
199                 return LZMA_PROG_ERROR;
200         }
201
202 out:
203         // Update the CRC32,
204         coder->crc32 = lzma_crc32(in + in_start,
205                         *in_pos - in_start, coder->crc32);
206
207         return ret;
208 }
209
210
211 static void
212 index_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
213 {
214         lzma_index_coder *coder = coder_ptr;
215         lzma_index_end(coder->index, allocator);
216         lzma_free(coder, allocator);
217         return;
218 }
219
220
221 static lzma_ret
222 index_decoder_memconfig(void *coder_ptr, uint64_t *memusage,
223                 uint64_t *old_memlimit, uint64_t new_memlimit)
224 {
225         lzma_index_coder *coder = coder_ptr;
226
227         *memusage = lzma_index_memusage(1, coder->count);
228         *old_memlimit = coder->memlimit;
229
230         if (new_memlimit != 0) {
231                 if (new_memlimit < *memusage)
232                         return LZMA_MEMLIMIT_ERROR;
233
234                 coder->memlimit = new_memlimit;
235         }
236
237         return LZMA_OK;
238 }
239
240
241 static lzma_ret
242 index_decoder_reset(lzma_index_coder *coder, const lzma_allocator *allocator,
243                 lzma_index **i, uint64_t memlimit)
244 {
245         // Remember the pointer given by the application. We will set it
246         // to point to the decoded Index only if decoding is successful.
247         // Before that, keep it NULL so that applications can always safely
248         // pass it to lzma_index_end() no matter did decoding succeed or not.
249         coder->index_ptr = i;
250         *i = NULL;
251
252         // We always allocate a new lzma_index.
253         coder->index = lzma_index_init(allocator);
254         if (coder->index == NULL)
255                 return LZMA_MEM_ERROR;
256
257         // Initialize the rest.
258         coder->sequence = SEQ_INDICATOR;
259         coder->memlimit = my_max(1, memlimit);
260         coder->count = 0; // Needs to be initialized due to _memconfig().
261         coder->pos = 0;
262         coder->crc32 = 0;
263
264         return LZMA_OK;
265 }
266
267
268 static lzma_ret
269 index_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
270                 lzma_index **i, uint64_t memlimit)
271 {
272         lzma_next_coder_init(&index_decoder_init, next, allocator);
273
274         if (i == NULL)
275                 return LZMA_PROG_ERROR;
276
277         lzma_index_coder *coder = next->coder;
278         if (coder == NULL) {
279                 coder = lzma_alloc(sizeof(lzma_index_coder), allocator);
280                 if (coder == NULL)
281                         return LZMA_MEM_ERROR;
282
283                 next->coder = coder;
284                 next->code = &index_decode;
285                 next->end = &index_decoder_end;
286                 next->memconfig = &index_decoder_memconfig;
287                 coder->index = NULL;
288         } else {
289                 lzma_index_end(coder->index, allocator);
290         }
291
292         return index_decoder_reset(coder, allocator, i, memlimit);
293 }
294
295
296 extern LZMA_API(lzma_ret)
297 lzma_index_decoder(lzma_stream *strm, lzma_index **i, uint64_t memlimit)
298 {
299         lzma_next_strm_init(index_decoder_init, strm, i, memlimit);
300
301         strm->internal->supported_actions[LZMA_RUN] = true;
302         strm->internal->supported_actions[LZMA_FINISH] = true;
303
304         return LZMA_OK;
305 }
306
307
308 extern LZMA_API(lzma_ret)
309 lzma_index_buffer_decode(lzma_index **i, uint64_t *memlimit,
310                 const lzma_allocator *allocator,
311                 const uint8_t *in, size_t *in_pos, size_t in_size)
312 {
313         // Sanity checks
314         if (i == NULL || memlimit == NULL
315                         || in == NULL || in_pos == NULL || *in_pos > in_size)
316                 return LZMA_PROG_ERROR;
317
318         // Initialize the decoder.
319         lzma_index_coder coder;
320         return_if_error(index_decoder_reset(&coder, allocator, i, *memlimit));
321
322         // Store the input start position so that we can restore it in case
323         // of an error.
324         const size_t in_start = *in_pos;
325
326         // Do the actual decoding.
327         lzma_ret ret = index_decode(&coder, allocator, in, in_pos, in_size,
328                         NULL, NULL, 0, LZMA_RUN);
329
330         if (ret == LZMA_STREAM_END) {
331                 ret = LZMA_OK;
332         } else {
333                 // Something went wrong, free the Index structure and restore
334                 // the input position.
335                 lzma_index_end(coder.index, allocator);
336                 *in_pos = in_start;
337
338                 if (ret == LZMA_OK) {
339                         // The input is truncated or otherwise corrupt.
340                         // Use LZMA_DATA_ERROR instead of LZMA_BUF_ERROR
341                         // like lzma_vli_decode() does in single-call mode.
342                         ret = LZMA_DATA_ERROR;
343
344                 } else if (ret == LZMA_MEMLIMIT_ERROR) {
345                         // Tell the caller how much memory would have
346                         // been needed.
347                         *memlimit = lzma_index_memusage(1, coder.count);
348                 }
349         }
350
351         return ret;
352 }