block_header_decoder.c revision 292588 
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
17static void
18free_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
33extern LZMA_API(lzma_ret)
34lzma_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}
125