fix(filesystem.romfs): improve end offset calculation.

unblob/handlers/filesystem/romfs.py

@@ -10,7 +10,7 @@
 
 from unblob.extractor import is_safe_path
 
-from ...file_utils import Endian, InvalidInputFormat, read_until_past, round_up
+from ...file_utils import Endian, InvalidInputFormat, round_up
 from ...models import Extractor, File, HexString, StructHandler, ValidChunk
 
 logger = get_logger()
@@ -25,6 +25,7 @@
 WORLD_RWX = 0o777
 ROMFS_HEADER_SIZE = 512
 ROMFS_SIGNATURE = b"-rom1fs-"
+PADDING_ALIGNMENT = 1024
 
 
 @unique
@@ -361,29 +362,31 @@ class RomFSFSHandler(StructHandler):
 
  def calculate_chunk(self, file: File, start_offset: int) -> Optional[ValidChunk]:
 
- if not valid_checksum(file.read(512)):
+ checksum = file.read(512)
+ if not valid_checksum(checksum):
  raise InvalidInputFormat("Invalid RomFS checksum.")
 
- file.seek(-512, io.SEEK_CUR)
+ file.seek(-len(checksum), io.SEEK_CUR)
 
  # Every multi byte value must be in big endian order.
  header = self.parse_header(file, Endian.BIG)
 
- # The zero terminated name of the volume, padded to 16 byte boundary.
- get_string(file)
-
- # seek filesystem size (number of accessible bytes in this fs)
- # from the actual end of the header
- file.seek(header.full_size, io.SEEK_CUR)
-
  # Another thing to note is that romfs works on file headers and data
  # aligned to 16 byte boundaries, but most hardware devices and the block
  # device drivers are unable to cope with smaller than block-sized data.
  # To overcome this limitation, the whole size of the file system must be
  # padded to an 1024 byte boundary.
- read_until_past(file, b"\x00")
+ end_offset = start_offset + round_up(
+ len(header) + header.full_size, PADDING_ALIGNMENT
+ )
+ fs_size = len(header) + header.full_size
+ padding_size = round_up(fs_size, PADDING_ALIGNMENT) - fs_size
+ if padding_size:
+ file.seek(start_offset + fs_size, io.SEEK_SET)
+ if file.read(padding_size) != bytes([0]) * padding_size:
+ raise InvalidInputFormat("Invalid padding.")
 
  return ValidChunk(
  start_offset=start_offset,
- end_offset=file.tell(),
+ end_offset=end_offset,
  )