contrib/xz/src/liblzma/common/block_header_decoder.c

   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, 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                 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         // Always zero for now.
  50         block->version = 0;
  51
  52         // Validate Block Header Size and Check type. The caller must have
  53         // already set these, so it is a programming error if this test fails.
  54         if (lzma_block_header_size_decode(in[0]) != block->header_size
  55                         || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX)
  56                 return LZMA_PROG_ERROR;
  57
  58         // Exclude the CRC32 field.
  59         const size_t in_size = block->header_size - 4;
  60
  61         // Verify CRC32
  62         if (lzma_crc32(in, in_size, 0) != unaligned_read32le(in + in_size))
  63                 return LZMA_DATA_ERROR;
  64
  65         // Check for unsupported flags.
  66         if (in[1] & 0x3C)
  67                 return LZMA_OPTIONS_ERROR;
  68
  69         // Start after the Block Header Size and Block Flags fields.
  70         size_t in_pos = 2;
  71
  72         // Compressed Size
  73         if (in[1] & 0x40) {
  74                 return_if_error(lzma_vli_decode(&block->compressed_size,
  75                                 NULL, in, &in_pos, in_size));
  76
  77                 // Validate Compressed Size. This checks that it isn't zero
  78                 // and that the total size of the Block is a valid VLI.
  79                 if (lzma_block_unpadded_size(block) == 0)
  80                         return LZMA_DATA_ERROR;
  81         } else {
  82                 block->compressed_size = LZMA_VLI_UNKNOWN;
  83         }
  84
  85         // Uncompressed Size
  86         if (in[1] & 0x80)
  87                 return_if_error(lzma_vli_decode(&block->uncompressed_size,
  88                                 NULL, in, &in_pos, in_size));
  89         else
  90                 block->uncompressed_size = LZMA_VLI_UNKNOWN;
  91
  92         // Filter Flags
  93         const size_t filter_count = (in[1] & 3) + 1;
  94         for (size_t i = 0; i < filter_count; ++i) {
  95                 const lzma_ret ret = lzma_filter_flags_decode(
  96                                 &block->filters[i], allocator,
  97                                 in, &in_pos, in_size);
  98                 if (ret != LZMA_OK) {
  99                         free_properties(block, allocator);
 100                         return ret;
 101                 }
 102         }
 103
 104         // Padding
 105         while (in_pos < in_size) {
 106                 if (in[in_pos++] != 0x00) {
 107                         free_properties(block, allocator);
 108
 109                         // Possibly some new field present so use
 110                         // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
 111                         return LZMA_OPTIONS_ERROR;
 112                 }
 113         }
 114
 115         return LZMA_OK;
 116 }