Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.11/site-packages/unblob/handlers/filesystem/cramfs.py: 100%

1import binascii 

2import struct 

3 

4from unblob.extractors import Command 

5 

6from ...file_utils import Endian, convert_int32, get_endian 

7from ...models import ( 

8 File, 

9 HandlerDoc, 

10 HandlerType, 

11 HexString, 

12 Reference, 

13 StructHandler, 

14 ValidChunk, 

15) 

16 

17CRAMFS_FLAG_FSID_VERSION_2 = 0x00000001 

18BIG_ENDIAN_MAGIC = 0x28_CD_3D_45 

19 

20 

21def swap_int32(i): 

22 return struct.unpack("<I", struct.pack(">I", i))[0] 

23 

24 

25class CramFSHandler(StructHandler): 

26 NAME = "cramfs" 

27 

28 PATTERNS = [ 

29 HexString("28 CD 3D 45"), # big endian 

30 HexString("45 3D CD 28"), # little endian 

31 ] 

32 

33 C_DEFINITIONS = r""" 

34 typedef struct cramfs_header { 

35 uint32 magic; 

36 uint32 size; 

37 uint32 flags; 

38 uint32 future; 

39 char signature[16]; 

40 uint32 fsid_crc; 

41 uint32 fsid_edition; 

42 uint32 fsid_blocks; 

43 uint32 fsid_files; 

44 char name[16]; 

45 } cramfs_header_t; 

46 """ 

47 HEADER_STRUCT = "cramfs_header_t" 

48 

49 EXTRACTOR = Command("7z", "x", "-y", "{inpath}", "-o{outdir}") 

50 

51 DOC = HandlerDoc( 

52 name="CramFS", 

53 description="CramFS is a lightweight, read-only file system format designed for simplicity and efficiency in embedded systems. It uses zlib compression for file data and stores metadata in a compact, contiguous structure.", 

54 handler_type=HandlerType.FILESYSTEM, 

55 vendor=None, 

56 references=[ 

57 Reference( 

58 title="CramFS Documentation", 

59 url="https://web.archive.org/web/20160304053532/http://sourceforge.net/projects/cramfs/", 

60 ), 

61 Reference( 

62 title="CramFS Wikipedia", 

63 url="https://en.wikipedia.org/wiki/Cramfs", 

64 ), 

65 ], 

66 limitations=[], 

67 ) 

68 

69 def calculate_chunk(self, file: File, start_offset: int) -> ValidChunk | None: 

70 endian = get_endian(file, BIG_ENDIAN_MAGIC) 

71 header = self.parse_header(file, endian) 

72 valid_signature = header.signature == b"Compressed ROMFS" 

73 

74 if valid_signature and self._is_crc_valid(file, start_offset, header, endian): 

75 return ValidChunk( 

76 start_offset=start_offset, 

77 end_offset=start_offset + header.size, 

78 ) 

79 return None 

80 

81 def _is_crc_valid( 

82 self, 

83 file: File, 

84 start_offset: int, 

85 header, 

86 endian: Endian, 

87 ) -> bool: 

88 # old cramfs format do not support crc 

89 if not (header.flags & CRAMFS_FLAG_FSID_VERSION_2): 

90 return True 

91 file.seek(start_offset) 

92 content = bytearray(file.read(header.size)) 

93 file.seek(start_offset + 32) 

94 crc_bytes = file.read(4) 

95 header_crc = convert_int32(crc_bytes, endian) 

96 content[32:36] = b"\x00\x00\x00\x00" 

97 computed_crc = binascii.crc32(content) 

98 # some vendors like their CRC's swapped, don't ask why 

99 return header_crc == computed_crc or header_crc == swap_int32(computed_crc)