Extracts .ros firmware files used by some netgear swtiches, eg: ng_gs728_52tp_516tp_bx-60116.ros

extract_ros.py

#!/usr/bin/env python3
import sys
import lzma
import crcmod
from struct import unpack, iter_unpack
from collections import namedtuple
from functools import partial
from tabulate import tabulate

crc32 = crcmod.predefined.mkPredefinedCrcFun('crc-32')

rosHdr = namedtuple("rosHdr", "magic model version crc pad")
Nghdr = namedtuple("NG022", "magic unk0 unk1 unk2 unk3 type pad")

def to_hex(data):
    if isinstance(data, int):
        return hex(data)
    return ''.join('%02x' % x for x in data)

def to_str(data):
    try:
        return bytes(data).decode().strip('\x00')
    except:
        return bytes(data)

def to_int(data):
    return int.from_bytes(data, "little")

def decompress(data):
    Decompressor = lzma.LZMADecompressor()
    out = Decompressor.decompress(data)
    return out


def ngunpack(data):
    defer = []
    table = []
    count = unpack("<I", data[0x20:0x24])[0]
    for name, offset, length, unknown, pad in iter_unpack("<16s 3I 4s", data[0x50:][:32*count]):
        name = to_str(name)
        length = length
        table.append((name, hex(offset), hex(length), hex(unknown), to_hex(pad)))

        if unknown == 0x0:
            section = data[offset:][:length]
        if unknown == 0x200:
            section = data[offset:][0x20:length]
            section = decompress(section)
            defer.append((name, partial(ng022, data[offset:][:length])))
        with open("out/"+name, "wb") as out:
            out.write(section)

    print()
    print(tabulate(table, headers=("Name", "Offset", "length", "compressed?", "Padding")))
    print()
    print("Compressed:")
    for name, func in defer:
        print(name.ljust(12), end="")
        func()


def ng022(data):
    hdr = Nghdr(*unpack("<8s4I4s4s", data[:0x20]))
    print(hdr[0].decode(), *[to_hex(x).ljust(10) for x in hdr[1:]])

    if hdr.type == b'PACK':
        ngunpack(data)


with open(sys.argv[1], "rb") as fd:
    data = memoryview(fd.read())

hdr = rosHdr(*unpack(">4s 20s 20s I 16s", data[:0x40]))

print("hdr:",   "%s (%s)" % (to_hex(hdr.magic), to_str(hdr.magic[:2])), sep='\t')
print("model:", to_str(hdr.model), sep='\t')
print("ver:",   to_str(hdr.version), sep='\t')
print("crc:",      hex(hdr.crc), sep='\t')
print("pad:",   to_hex(hdr.pad), sep='\t')

if hdr.crc != crc32(data[0x40:]):
    print("BAD CRC")

print()

ng022(data[0x40:])

exit()