357 lines
12 KiB
Python
Executable file
357 lines
12 KiB
Python
Executable file
#!/usr/bin/env python3
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import os
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import sys
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import hashlib
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import struct
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import argparse
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class VmaHeader():
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def __init__(self, fo, skip_hash):
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# 0 - 3: magic
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# VMA magic string ("VMA\x00")
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magic = fo.read(4)
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assert magic == b'VMA\0'
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# 4 - 7: version
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# Version number (valid value is 1)
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version = int.from_bytes(fo.read(4), 'big')
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assert version == 1
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# 8 - 23: uuid
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# Unique ID, Same uuid is used to mark extents.
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self.uuid = fo.read(16)
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# 24 - 31: ctime
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# Backup time stamp (seconds since epoch)
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self.ctime = int.from_bytes(fo.read(8), 'big')
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# 32 - 47: md5sum
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# Header checksum (from byte 0 to header_size). This field
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# is filled with zero to generate the checksum.
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self.md5sum = fo.read(16)
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# 48 - 51: blob_buffer_offset
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# Start of blob buffer (multiple of 512)
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self.blob_buffer_offset = int.from_bytes(fo.read(4), 'big')
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# 52 - 55: blob_buffer_size
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# Size of blob buffer (multiple of 512)
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self.blob_buffer_size = int.from_bytes(fo.read(4), 'big')
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# 56 - 59: header_size
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# Overall size of this header (multiple of 512)
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self.header_size = int.from_bytes(fo.read(4), 'big')
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# 60 - 2043: reserved
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fo.seek(1984, os.SEEK_CUR)
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# 2044 - 3067: uint32_t config_names[256]
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# Offsets into blob_buffer table
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self.config_names = []
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for i in range(256):
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self.config_names.append(int.from_bytes(fo.read(4), 'big'))
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# 3068 - 4091: uint32_t config_data[256]
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# Offsets into blob_buffer table
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self.config_data = []
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for i in range(256):
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self.config_data.append(int.from_bytes(fo.read(4), 'big'))
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# 4092 - 4095: reserved
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fo.seek(4, os.SEEK_CUR)
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# 4096 - 12287: VmaDeviceInfoHeader dev_info[256]
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# The offset in this table is used as 'dev_id' inside
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# the data streams.
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self.dev_info = []
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for i in range(256):
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self.dev_info.append(VmaDeviceInfoHeader(fo, self))
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# 12288 - header_size: Blob buffer
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# the blob buffer layout is very odd. there appears to be an additional
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# byte of padding at the beginning
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fo.seek(1, os.SEEK_CUR)
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# since byte-wise offsets are used to address the blob buffer, the
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# blob metadata is stored in a hashmap, with the offsets as the keys
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self.blob_buffer = {}
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blob_buffer_current_offset = 1
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while(fo.tell() < self.blob_buffer_offset + self.blob_buffer_size):
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self.blob_buffer[blob_buffer_current_offset] = Blob(fo)
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blob_buffer_current_offset = fo.tell() - self.blob_buffer_offset
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# make sure the file object points at the end of the vma header
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fo.seek(self.header_size, os.SEEK_SET)
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# reread the header and generate a md5 checksum of the data
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if skip_hash:
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self.generated_md5sum = None
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else:
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self.generated_md5sum = self.__gen_md5sum(fo)
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def __gen_md5sum(self, fo):
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p = fo.tell()
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fo.seek(0, os.SEEK_SET)
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h = hashlib.md5()
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data = fo.read(self.header_size)
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data = data[:32] + b'\0' * 16 + data[48:]
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h.update(data)
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fo.seek(p, os.SEEK_SET)
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return h.digest()
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class VmaDeviceInfoHeader():
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def __init__(self, fo, vma_header):
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self.__vma_header = vma_header
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# 0 - 3: devive name (offsets into blob_buffer table)
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self.device_name = int.from_bytes(fo.read(4), 'big')
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# 4 - 7: reserved
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fo.seek(4, os.SEEK_CUR)
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# 8 - 15: device size in bytes
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self.device_size = int.from_bytes(fo.read(8), 'big')
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# 16 - 31: reserved
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fo.seek(16, os.SEEK_CUR)
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def get_name(self):
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name = self.__vma_header.blob_buffer[self.device_name].data
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return name.split(b'\0')[0].decode('utf-8')
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class VmaExtentHeader():
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def __init__(self, fo, vma_header, skip_hash):
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self.pos_start = fo.tell()
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# 0 - 3: magic
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# VMA extent magic string ("VMAE")
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magic = fo.read(4)
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assert magic == b'VMAE'
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# 4 - 5: reserved
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fo.seek(2, os.SEEK_CUR)
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# 6 - 7: block_count
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# Overall number of contained 4K block
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self.block_count = int.from_bytes(fo.read(2), 'big')
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# 8 - 23: uuid
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# Unique ID, Same uuid as used in the VMA header.
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self.uuid = fo.read(16)
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# 24 - 39: md5sum
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# Header checksum (from byte 0 to header_size). This field
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# is filled with zero to generate the checksum.
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self.md5sum = fo.read(16)
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# 40 - 511: blockinfo[59]
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self.blockinfo = []
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for i in range(59):
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self.blockinfo.append(Blockinfo(fo, vma_header))
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self.pos_end = fo.tell()
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if skip_hash:
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self.generated_md5sum = None
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else:
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self.generated_md5sum = self.__gen_md5sum(fo)
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def __gen_md5sum(self, fo):
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p = fo.tell()
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fo.seek(self.pos_start, os.SEEK_SET)
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h = hashlib.md5()
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data = fo.read(self.pos_end - self.pos_start)
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data = data[:24] + b'\0' * 16 + data[40:]
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h.update(data)
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fo.seek(p, os.SEEK_SET)
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return h.digest()
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class Blob():
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def __init__(self, fo):
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# the size of a blob is a two-byte int in LITTLE endian
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# source: original c code of vma-reader
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# uint32_t size = vmar->head_data[bstart] +
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# (vmar->head_data[bstart+1] << 8);
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self.size = int.from_bytes(fo.read(2), 'little')
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self.data = fo.read(self.size)
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class Blockinfo():
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CLUSTER_SIZE = 65536
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def __init__(self, fo, vma_header):
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self.__vma_header = vma_header
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# 0 - 1: mask
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self.mask = int.from_bytes(fo.read(2), 'big')
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# 2: reserved
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fo.seek(1, os.SEEK_CUR)
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# 3: dev_id
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# Device ID (offset into dev_info table)
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self.dev_id = int.from_bytes(fo.read(1), 'big')
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# 4 - 7: cluster_num
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self.cluster_num = int.from_bytes(fo.read(4), 'big')
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def extract_configs(fo, args, vma_header):
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"""
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Configs in VMA are composed of two blobs. One specifies the config's
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filename and the other contains the config's content.
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The filename seems to be a null-terminated string, while the content is not
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terminated.
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"""
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if args.verbose: print('extracting configs...')
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for i in range(256):
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if vma_header.config_names[i] == 0: continue
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config_name = vma_header.blob_buffer[vma_header.config_names[i]].data
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# interpret filename as a null-terminated utf-8 string
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config_name = config_name.split(b'\0')[0].decode('utf-8')
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if args.verbose: print(f'{config_name}...', end='')
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config_data = vma_header.blob_buffer[vma_header.config_data[i]].data
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with open(os.path.join(args.destination, config_name), 'wb') as config_fo:
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config_fo.write(config_data)
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if args.verbose: print(' OK')
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def extract(fo, args):
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os.makedirs(args.destination, exist_ok=True)
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fo.seek(0, os.SEEK_END)
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filesize = fo.tell()
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fo.seek(0, os.SEEK_SET)
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vma_header = VmaHeader(fo, args.skip_hash)
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# check the md5 checksum given in the header with the value calculated from
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# the file
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if vma_header.generated_md5sum is not None:
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assert vma_header.md5sum == vma_header.generated_md5sum
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extract_configs(fo, args, vma_header)
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# extract_configs may move the read head somewhere into the blob buffer
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# make sure we are back at the end of the header
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fo.seek(vma_header.header_size, os.SEEK_SET)
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if args.verbose: print('extracting devices...')
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# open file handlers for all devices within the VMA
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# so we can easily append data to arbitrary devices
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device_fos = {}
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for dev_id, dev_info in enumerate(vma_header.dev_info):
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if dev_info.device_size > 0:
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if args.verbose: print(dev_info.get_name())
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device_fos[dev_id] = open(os.path.join(args.destination, dev_info.get_name()), 'wb')
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if args.verbose: print('this may take a while...')
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# used for sanity checking
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cluster_num_prev = -1
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while(fo.tell() < filesize):
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# when there is data to read at this point, we can safely expect a full
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# extent header with additional clusters
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extent_header = VmaExtentHeader(fo, vma_header, args.skip_hash)
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assert vma_header.uuid == extent_header.uuid
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# check the md5 checksum given in the header with the value calculated from
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# the file
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if extent_header.generated_md5sum is not None:
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assert extent_header.md5sum == extent_header.generated_md5sum
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for blockinfo in extent_header.blockinfo:
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if blockinfo.dev_id == 0: continue
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device_fo = device_fos[blockinfo.dev_id]
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# non-sequential clusters encountered, handle this case
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if blockinfo.cluster_num != cluster_num_prev + 1:
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if args.verbose: print('non sequential cluster encountered...')
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cluster_pos = blockinfo.cluster_num * Blockinfo.CLUSTER_SIZE
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if blockinfo.cluster_num > cluster_num_prev:
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# special case: cluster num is larger than current,
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# seek forward into file AND, if needed, fill missing size
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# with zeros
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device_fo.seek(0, os.SEEK_END)
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written_size = device_fo.tell()
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if written_size < cluster_pos:
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# add padding for missing clusters
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if args.verbose:
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print(f'{blockinfo.cluster_num}')
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print(f'adding {cluster_pos - written_size} bytes'
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+ 'of padding...')
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# write padding in chucks of 4096 bytes to avoid
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# memory errors
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padding = cluster_pos - written_size
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while padding > 0:
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device_fo.write(b'\0' * min(padding, 4096))
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padding -= 4096
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# seek to start of new cluster
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device_fo.seek(cluster_pos, os.SEEK_SET)
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cluster_num_prev = blockinfo.cluster_num
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for i in range(16):
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# a 2-bytes wide bitmask indicates 4k blocks with only zeros
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if (1 << i) & blockinfo.mask:
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device_fo.write(fo.read(4096))
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else:
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device_fo.write(b'\0' * 4096)
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if args.verbose: print('closing file handles...')
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for device_fo in device_fos.values():
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device_fo.close()
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if args.verbose: print('done')
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def main():
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parser = argparse.ArgumentParser()
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parser.add_argument('filename', type=str)
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parser.add_argument('destination', type=str)
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parser.add_argument('-v', '--verbose', default=False, action='store_true')
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parser.add_argument('-f', '--force', default=False, action='store_true',
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help='overwrite target file if it exists')
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parser.add_argument('--skip-hash', default=False, action='store_true',
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help='do not perform md5 checksum test of data')
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args = parser.parse_args()
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if(not os.path.exists(args.filename)):
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print('Error! Source file does not exist!')
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return 1
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if(os.path.exists(args.destination) and not args.force):
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print('Error! Destination path exists!')
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return 1
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with open(args.filename, 'rb') as fo:
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extract(fo, args)
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return 0
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if __name__ == '__main__':
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sys.exit(main())
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