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) != 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] & 3U) + 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