1///////////////////////////////////////////////////////////////////////////////
2//
3/// \file       stream_flags_decoder.c
4/// \brief      Decodes Stream Header and Stream Footer 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 "stream_flags_common.h"
14
15
16static bool
17stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
18{
19	// Reserved bits must be unset.
20	if (in[0] != 0x00 || (in[1] & 0xF0))
21		return true;
22
23	options->version = 0;
24	options->check = in[1] & 0x0F;
25
26	return false;
27}
28
29
30extern LZMA_API(lzma_ret)
31lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
32{
33	// Magic
34	if (memcmp(in, lzma_header_magic, sizeof(lzma_header_magic)) != 0)
35		return LZMA_FORMAT_ERROR;
36
37	// Verify the CRC32 so we can distinguish between corrupt
38	// and unsupported files.
39	const uint32_t crc = lzma_crc32(in + sizeof(lzma_header_magic),
40			LZMA_STREAM_FLAGS_SIZE, 0);
41	if (crc != read32le(in + sizeof(lzma_header_magic)
42			+ LZMA_STREAM_FLAGS_SIZE)) {
43#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
44		return LZMA_DATA_ERROR;
45#endif
46	}
47
48	// Stream Flags
49	if (stream_flags_decode(options, in + sizeof(lzma_header_magic)))
50		return LZMA_OPTIONS_ERROR;
51
52	// Set Backward Size to indicate unknown value. That way
53	// lzma_stream_flags_compare() can be used to compare Stream Header
54	// and Stream Footer while keeping it useful also for comparing
55	// two Stream Footers.
56	options->backward_size = LZMA_VLI_UNKNOWN;
57
58	return LZMA_OK;
59}
60
61
62extern LZMA_API(lzma_ret)
63lzma_stream_footer_decode(lzma_stream_flags *options, const uint8_t *in)
64{
65	// Magic
66	if (memcmp(in + sizeof(uint32_t) * 2 + LZMA_STREAM_FLAGS_SIZE,
67			lzma_footer_magic, sizeof(lzma_footer_magic)) != 0)
68		return LZMA_FORMAT_ERROR;
69
70	// CRC32
71	const uint32_t crc = lzma_crc32(in + sizeof(uint32_t),
72			sizeof(uint32_t) + LZMA_STREAM_FLAGS_SIZE, 0);
73	if (crc != read32le(in)) {
74#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
75		return LZMA_DATA_ERROR;
76#endif
77	}
78
79	// Stream Flags
80	if (stream_flags_decode(options, in + sizeof(uint32_t) * 2))
81		return LZMA_OPTIONS_ERROR;
82
83	// Backward Size
84	options->backward_size = read32le(in + sizeof(uint32_t));
85	options->backward_size = (options->backward_size + 1) * 4;
86
87	return LZMA_OK;
88}
89