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) 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