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[zpackage] / lzma / common / block_header_decoder.c
1 ///////////////////////////////////////////////////////////////////////////////
2 //
3 /// \file       block_header_decoder.c
4 /// \brief      Decodes Block Header from .xz files
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 "common.h"
14 #include "check.h"
15
16
17 static void
18 free_properties(lzma_block *block, const lzma_allocator *allocator)
19 {
20         // Free allocated filter options. The last array member is not
21         // touched after the initialization in the beginning of
22         // lzma_block_header_decode(), so we don't need to touch that here.
23         for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i) {
24                 lzma_free(block->filters[i].options, allocator);
25                 block->filters[i].id = LZMA_VLI_UNKNOWN;
26                 block->filters[i].options = NULL;
27         }
28
29         return;
30 }
31
32
33 extern LZMA_API(lzma_ret)
34 lzma_block_header_decode(lzma_block *block,
35                 const lzma_allocator *allocator, const uint8_t *in)
36 {
37         // NOTE: We consider the header to be corrupt not only when the
38         // CRC32 doesn't match, but also when variable-length integers
39         // are invalid or over 63 bits, or if the header is too small
40         // to contain the claimed information.
41
42         // Initialize the filter options array. This way the caller can
43         // safely free() the options even if an error occurs in this function.
44         for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) {
45                 block->filters[i].id = LZMA_VLI_UNKNOWN;
46                 block->filters[i].options = NULL;
47         }
48
49         // Versions 0 and 1 are supported. If a newer version was specified,
50         // we need to downgrade it.
51         if (block->version > 1)
52                 block->version = 1;
53
54         // This isn't a Block Header option, but since the decompressor will
55         // read it if version >= 1, it's better to initialize it here than
56         // to expect the caller to do it since in almost all cases this
57         // should be false.
58         block->ignore_check = false;
59
60         // Validate Block Header Size and Check type. The caller must have
61         // already set these, so it is a programming error if this test fails.
62         if (lzma_block_header_size_decode(in[0]) != block->header_size
63                         || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX)
64                 return LZMA_PROG_ERROR;
65
66         // Exclude the CRC32 field.
67         const size_t in_size = block->header_size - 4;
68
69         // Verify CRC32
70         if (lzma_crc32(in, in_size, 0) != unaligned_read32le(in + in_size))
71                 return LZMA_DATA_ERROR;
72
73         // Check for unsupported flags.
74         if (in[1] & 0x3C)
75                 return LZMA_OPTIONS_ERROR;
76
77         // Start after the Block Header Size and Block Flags fields.
78         size_t in_pos = 2;
79
80         // Compressed Size
81         if (in[1] & 0x40) {
82                 return_if_error(lzma_vli_decode(&block->compressed_size,
83                                 NULL, in, &in_pos, in_size));
84
85                 // Validate Compressed Size. This checks that it isn't zero
86                 // and that the total size of the Block is a valid VLI.
87                 if (lzma_block_unpadded_size(block) == 0)
88                         return LZMA_DATA_ERROR;
89         } else {
90                 block->compressed_size = LZMA_VLI_UNKNOWN;
91         }
92
93         // Uncompressed Size
94         if (in[1] & 0x80)
95                 return_if_error(lzma_vli_decode(&block->uncompressed_size,
96                                 NULL, in, &in_pos, in_size));
97         else
98                 block->uncompressed_size = LZMA_VLI_UNKNOWN;
99
100         // Filter Flags
101         const size_t filter_count = (in[1] & 3) + 1;
102         for (size_t i = 0; i < filter_count; ++i) {
103                 const lzma_ret ret = lzma_filter_flags_decode(
104                                 &block->filters[i], allocator,
105                                 in, &in_pos, in_size);
106                 if (ret != LZMA_OK) {
107                         free_properties(block, allocator);
108                         return ret;
109                 }
110         }
111
112         // Padding
113         while (in_pos < in_size) {
114                 if (in[in_pos++] != 0x00) {
115                         free_properties(block, allocator);
116
117                         // Possibly some new field present so use
118                         // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
119                         return LZMA_OPTIONS_ERROR;
120                 }
121         }
122
123         return LZMA_OK;
124 }