src/liblzma/common/stream_flags_decoder.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 ///////////////////////////////////////////////////////////////////////////////
   4 //
   5 /// \file       stream_flags_decoder.c
   6 /// \brief      Decodes Stream Header and Stream Footer from .xz files
   7 //
   8 //  Author:     Lasse Collin
   9 //
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 #include "stream_flags_common.h"
  13
  14
  15 static bool
  16 stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
  17 {
  18         // Reserved bits must be unset.
  19         if (in[0] != 0x00 || (in[1] & 0xF0))
  20                 return true;
  21
  22         options->version = 0;
  23         options->check = in[1] & 0x0F;
  24
  25         return false;
  26 }
  27
  28
  29 extern LZMA_API(lzma_ret)
  30 lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
  31 {
  32         // Magic
  33         if (memcmp(in, lzma_header_magic, sizeof(lzma_header_magic)) != 0)
  34                 return LZMA_FORMAT_ERROR;
  35
  36         // Verify the CRC32 so we can distinguish between corrupt
  37         // and unsupported files.
  38         const uint32_t crc = lzma_crc32(in + sizeof(lzma_header_magic),
  39                         LZMA_STREAM_FLAGS_SIZE, 0);
  40         if (crc != read32le(in + sizeof(lzma_header_magic)
  41                         + LZMA_STREAM_FLAGS_SIZE)) {
  42 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
  43                 return LZMA_DATA_ERROR;
  44 #endif
  45         }
  46
  47         // Stream Flags
  48         if (stream_flags_decode(options, in + sizeof(lzma_header_magic)))
  49                 return LZMA_OPTIONS_ERROR;
  50
  51         // Set Backward Size to indicate unknown value. That way
  52         // lzma_stream_flags_compare() can be used to compare Stream Header
  53         // and Stream Footer while keeping it useful also for comparing
  54         // two Stream Footers.
  55         options->backward_size = LZMA_VLI_UNKNOWN;
  56
  57         return LZMA_OK;
  58 }
  59
  60
  61 extern LZMA_API(lzma_ret)
  62 lzma_stream_footer_decode(lzma_stream_flags *options, const uint8_t *in)
  63 {
  64         // Magic
  65         if (memcmp(in + sizeof(uint32_t) * 2 + LZMA_STREAM_FLAGS_SIZE,
  66                         lzma_footer_magic, sizeof(lzma_footer_magic)) != 0)
  67                 return LZMA_FORMAT_ERROR;
  68
  69         // CRC32
  70         const uint32_t crc = lzma_crc32(in + sizeof(uint32_t),
  71                         sizeof(uint32_t) + LZMA_STREAM_FLAGS_SIZE, 0);
  72         if (crc != read32le(in)) {
  73 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
  74                 return LZMA_DATA_ERROR;
  75 #endif
  76         }
  77
  78         // Stream Flags
  79         if (stream_flags_decode(options, in + sizeof(uint32_t) * 2))
  80                 return LZMA_OPTIONS_ERROR;
  81
  82         // Backward Size
  83         options->backward_size = read32le(in + sizeof(uint32_t));
  84         options->backward_size = (options->backward_size + 1) * 4;
  85
  86         return LZMA_OK;
  87 }