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 extern LZMA_API(lzma_ret) 18 lzma_block_header_decode(lzma_block *block, 19 const lzma_allocator *allocator, const uint8_t *in) 20 { 21 // NOTE: We consider the header to be corrupt not only when the 22 // CRC32 doesn't match, but also when variable-length integers 23 // are invalid or over 63 bits, or if the header is too small 24 // to contain the claimed information. 25 26 // Catch unexpected NULL pointers. 27 if (block == NULL || block->filters == NULL || in == NULL) 28 return LZMA_PROG_ERROR; 29 30 // Initialize the filter options array. This way the caller can 31 // safely free() the options even if an error occurs in this function. 32 for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) { 33 block->filters[i].id = LZMA_VLI_UNKNOWN; 34 block->filters[i].options = NULL; 35 } 36 37 // Versions 0 and 1 are supported. If a newer version was specified, 38 // we need to downgrade it. 39 if (block->version > 1) 40 block->version = 1; 41 42 // This isn't a Block Header option, but since the decompressor will 43 // read it if version >= 1, it's better to initialize it here than 44 // to expect the caller to do it since in almost all cases this 45 // should be false. 46 block->ignore_check = false; 47 48 // Validate Block Header Size and Check type. The caller must have 49 // already set these, so it is a programming error if this test fails. 50 if (lzma_block_header_size_decode(in[0]) != block->header_size 51 || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX) 52 return LZMA_PROG_ERROR; 53 54 // Exclude the CRC32 field. 55 const size_t in_size = block->header_size - 4; 56 57 // Verify CRC32 58 if (lzma_crc32(in, in_size, 0) != read32le(in + in_size)) { 59 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION 60 return LZMA_DATA_ERROR; 61 #endif 62 } 63 64 // Check for unsupported flags. 65 if (in[1] & 0x3C) 66 return LZMA_OPTIONS_ERROR; 67 68 // Start after the Block Header Size and Block Flags fields. 69 size_t in_pos = 2; 70 71 // Compressed Size 72 if (in[1] & 0x40) { 73 return_if_error(lzma_vli_decode(&block->compressed_size, 74 NULL, in, &in_pos, in_size)); 75 76 // Validate Compressed Size. This checks that it isn't zero 77 // and that the total size of the Block is a valid VLI. 78 if (lzma_block_unpadded_size(block) == 0) 79 return LZMA_DATA_ERROR; 80 } else { 81 block->compressed_size = LZMA_VLI_UNKNOWN; 82 } 83 84 // Uncompressed Size 85 if (in[1] & 0x80) 86 return_if_error(lzma_vli_decode(&block->uncompressed_size, 87 NULL, in, &in_pos, in_size)); 88 else 89 block->uncompressed_size = LZMA_VLI_UNKNOWN; 90 91 // Filter Flags 92 const size_t filter_count = (in[1] & 3U) + 1; 93 for (size_t i = 0; i < filter_count; ++i) { 94 const lzma_ret ret = lzma_filter_flags_decode( 95 &block->filters[i], allocator, 96 in, &in_pos, in_size); 97 if (ret != LZMA_OK) { 98 lzma_filters_free(block->filters, allocator); 99 return ret; 100 } 101 } 102 103 // Padding 104 while (in_pos < in_size) { 105 if (in[in_pos++] != 0x00) { 106 lzma_filters_free(block->filters, allocator); 107 108 // Possibly some new field present so use 109 // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR. 110 return LZMA_OPTIONS_ERROR; 111 } 112 } 113 114 return LZMA_OK; 115 } 116