1 // SPDX-License-Identifier: 0BSD
2
3 ///////////////////////////////////////////////////////////////////////////////
4 //
5 /// \file block_header_decoder.c
6 /// \brief Decodes Block Header from .xz files
7 //
8 // Author: Lasse Collin
9 //
10 ///////////////////////////////////////////////////////////////////////////////
11
12 #include "common.h"
13 #include "check.h"
14
15
16 extern LZMA_API(lzma_ret)
lzma_block_header_decode(lzma_block * block,const lzma_allocator * allocator,const uint8_t * in)17 lzma_block_header_decode(lzma_block *block,
18 const lzma_allocator *allocator, const uint8_t *in)
19 {
20 // NOTE: We consider the header to be corrupt not only when the
21 // CRC32 doesn't match, but also when variable-length integers
22 // are invalid or over 63 bits, or if the header is too small
23 // to contain the claimed information.
24
25 // Catch unexpected NULL pointers.
26 if (block == NULL || block->filters == NULL || in == NULL)
27 return LZMA_PROG_ERROR;
28
29 // Initialize the filter options array. This way the caller can
30 // safely free() the options even if an error occurs in this function.
31 for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) {
32 block->filters[i].id = LZMA_VLI_UNKNOWN;
33 block->filters[i].options = NULL;
34 }
35
36 // Versions 0 and 1 are supported. If a newer version was specified,
37 // we need to downgrade it.
38 if (block->version > 1)
39 block->version = 1;
40
41 // This isn't a Block Header option, but since the decompressor will
42 // read it if version >= 1, it's better to initialize it here than
43 // to expect the caller to do it since in almost all cases this
44 // should be false.
45 block->ignore_check = false;
46
47 // Validate Block Header Size and Check type. The caller must have
48 // already set these, so it is a programming error if this test fails.
49 if (lzma_block_header_size_decode(in[0]) != block->header_size
50 || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX)
51 return LZMA_PROG_ERROR;
52
53 // Exclude the CRC32 field.
54 const size_t in_size = block->header_size - 4;
55
56 // Verify CRC32
57 if (lzma_crc32(in, in_size, 0) != read32le(in + in_size)) {
58 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
59 return LZMA_DATA_ERROR;
60 #endif
61 }
62
63 // Check for unsupported flags.
64 if (in[1] & 0x3C)
65 return LZMA_OPTIONS_ERROR;
66
67 // Start after the Block Header Size and Block Flags fields.
68 size_t in_pos = 2;
69
70 // Compressed Size
71 if (in[1] & 0x40) {
72 return_if_error(lzma_vli_decode(&block->compressed_size,
73 NULL, in, &in_pos, in_size));
74
75 // Validate Compressed Size. This checks that it isn't zero
76 // and that the total size of the Block is a valid VLI.
77 if (lzma_block_unpadded_size(block) == 0)
78 return LZMA_DATA_ERROR;
79 } else {
80 block->compressed_size = LZMA_VLI_UNKNOWN;
81 }
82
83 // Uncompressed Size
84 if (in[1] & 0x80)
85 return_if_error(lzma_vli_decode(&block->uncompressed_size,
86 NULL, in, &in_pos, in_size));
87 else
88 block->uncompressed_size = LZMA_VLI_UNKNOWN;
89
90 // Filter Flags
91 const size_t filter_count = (in[1] & 3U) + 1;
92 for (size_t i = 0; i < filter_count; ++i) {
93 const lzma_ret ret = lzma_filter_flags_decode(
94 &block->filters[i], allocator,
95 in, &in_pos, in_size);
96 if (ret != LZMA_OK) {
97 lzma_filters_free(block->filters, allocator);
98 return ret;
99 }
100 }
101
102 // Padding
103 while (in_pos < in_size) {
104 if (in[in_pos++] != 0x00) {
105 lzma_filters_free(block->filters, allocator);
106
107 // Possibly some new field present so use
108 // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
109 return LZMA_OPTIONS_ERROR;
110 }
111 }
112
113 return LZMA_OK;
114 }
115