112 lines
3.5 KiB
Python
112 lines
3.5 KiB
Python
import os
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import io
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from .matcher import SignatureMatcher, Match
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class CromFS(SignatureMatcher):
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"""
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CromFS a readonly file system
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little-endian
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https://github.com/deadsy/nuttx/blob/master/tools/gencromfs.c
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this should be more correct?
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https://gitea.hedron.io/pixy2040/nuttx/src/branch/master/tools/gencromfs.c
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this CromFS might be a little bit different from the CROMFS here
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https://bisqwit.iki.fi/src/cromfs-format.txt
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this ^ has the signature CROMFS03 and probably CROMFS02 for v2
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this ^ is big-endian
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"""
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def __init__(self, file):
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self.name = "CromFS"
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self.signature = b'CROM'
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super().__init__(file)
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def is_valid(self):
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for match in self.search():
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start = match
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header = io.BytesIO(self.file[start:start+20])
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magic = header.read(4)
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nnodes = header.read(2)
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nblocks = header.read(2)
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root = header.read(4)
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fsize = header.read(4)
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bsize = header.read(4)
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as_num = lambda x: int.from_bytes(x, 'little')
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nnodes = as_num(nnodes)
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nblocks = as_num(nblocks)
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root = as_num(root)
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fsize = as_num(fsize)
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bsize = as_num(bsize)
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if root != 20:
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continue
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data = {
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'nnodes': nnodes,
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'nblocks': nblocks,
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'root': root,
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'bsize': bsize,
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}
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self.matches += [Match(start, fsize, data)]
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return len(self.matches) != 0
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def view(self, match):
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as_num = lambda x: int.from_bytes(x, 'little')
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root = match.data['root']
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bsize = match.data['bsize']
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nblocks = match.data['nblocks']
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nnodes = match.data['nnodes']
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region = io.BytesIO(self.file[match.offset : match.offset + match.length])
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region.seek(root, os.SEEK_SET)
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def read_str_at(buffer, at=None, recover=False):
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if at == 0 or at is None:
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return ''
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s = b''
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old = buffer.tell()
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if at:
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buffer.seek(at, os.SEEK_SET)
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while True:
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c = buffer.read(1)
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if c == b'\x00':
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break
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s += c
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if recover:
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buffer.seek(old, os.SEEK_SET)
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return s.decode()
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def read_nodes(buffer, current):
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mode = as_num(buffer.read(2))
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buffer.read(2)
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name_offset = as_num(buffer.read(4))
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size = as_num(buffer.read(4))
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peer = as_num(buffer.read(4))
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extra = as_num(buffer.read(4))
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name = read_str_at(buffer, at=name_offset, recover=True)
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is_dir = lambda mode: mode & (4 << 12) != 0
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is_reg = lambda mode: mode & (8 << 12) != 0
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is_link = lambda mode: mode & (10 << 12) != 0
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path = current + '/' + name
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print(path)
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if is_link(mode):
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pass
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if is_dir(mode):
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# traverse the directory children
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buffer.seek(extra, os.SEEK_SET)
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read_nodes(buffer, current + '/' + name)
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if is_reg(mode):
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for block in range(extra):
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# decrypt each block
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pass
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# traverse its peer
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if peer != 0:
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buffer.seek(peer, os.SEEK_SET)
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read_nodes(buffer, current)
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read_nodes(region, '')
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