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270
test/ext4lib.py
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270
test/ext4lib.py
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#!/usr/bin/env python3
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"""
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EXT4 Filesystem Libraries
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"""
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import struct, os, sys, stat
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from pathlib import Path
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BLOCK=4096
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def read_at(f, offset, size):
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f.seek(offset)
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return f.read(size)
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def parse_superblock(data):
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sb = {}
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sb['inodes_count'] = struct.unpack_from('<I', data, 0)[0]
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sb['blocks_count'] = struct.unpack_from('<I', data, 4)[0]
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sb['blocks_per_group'] = struct.unpack_from('<I', data, 32)[0]
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sb['inodes_per_group'] = struct.unpack_from('<I', data, 40)[0]
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sb['inode_size'] = struct.unpack_from('<H', data, 88)[0]
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sb['magic'] = struct.unpack_from('<H', data, 56)[0]
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sb['desc_size'] = struct.unpack_from('<H', data, 254)[0] or 32
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return sb
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def parse_gdt_entry(gdt_data, offset, desc_size):
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lo = struct.unpack_from('<I', gdt_data, offset + 8)[0]
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if desc_size >= 64:
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hi = struct.unpack_from('<I', gdt_data, offset + 40)[0]
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return lo | (hi << 32)
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return lo
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def parse_extent_tree(data, inode_offset):
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base = inode_offset + 40
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magic, entries, _, depth = struct.unpack_from('<HHHH', data, base)
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if magic != 0xF30A:
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return []
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extents = []
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if depth == 0:
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for i in range(min(entries, 4)):
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o = base + 12 + i * 12
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if o + 12 > len(data): break
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l_block = struct.unpack_from('<I', data, o )[0]
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ee_len = struct.unpack_from('<H', data, o + 4)[0]
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start_hi = struct.unpack_from('<H', data, o + 6)[0]
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start_lo = struct.unpack_from('<I', data, o + 8)[0]
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phys = (start_hi << 32) | start_lo
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if phys > 0:
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extents.append((l_block, phys, ee_len & 0x7FFF))
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else:
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# Depth > 0: extent index node - follow first child
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# (handles large dirs gracefully)
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o = base + 12
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ei_leaf_lo = struct.unpack_from('<I', data, o + 4)[0]
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ei_leaf_hi = struct.unpack_from('<H', data, o + 8)[0]
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extents.append((0, (ei_leaf_hi << 32) | ei_leaf_lo, 1))
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return extents
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def read_extent_tree_blocks(f, data, inode_offset):
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"""
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Fully recursive extent tree walker.
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Returns sorted list of (logical_block, phys_block) pairs.
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"""
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base = inode_offset + 40
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magic, entries, _, depth = struct.unpack_from('<HHHH', data, base)
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if magic != 0xF30A:
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return []
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return _walk_extent_node(f, data, base, depth)
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def _walk_extent_node(f, data, base, depth):
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magic, entries, _, _ = struct.unpack_from('<HHHH', data, base)
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if magic != 0xF30A:
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return []
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result = []
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if depth == 0:
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# Leaf node - actual extents
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for i in range(entries):
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o = base + 12 + i * 12
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l_block = struct.unpack_from('<I', data, o )[0]
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ee_len = struct.unpack_from('<H', data, o + 4)[0]
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start_hi = struct.unpack_from('<H', data, o + 6)[0]
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start_lo = struct.unpack_from('<I', data, o + 8)[0]
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phys = (start_hi << 32) | start_lo
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if phys > 0:
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for b in range(ee_len & 0x7FFF):
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result.append((l_block + b, phys + b))
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else:
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# Index node - recurse into each child
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for i in range(entries):
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o = base + 12 + i * 12
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leaf_lo = struct.unpack_from('<I', data, o + 4)[0]
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leaf_hi = struct.unpack_from('<H', data, o + 8)[0]
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leaf_block = (leaf_hi << 32) | leaf_lo
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try:
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child_data = read_at(f, leaf_block * BLOCK, BLOCK)
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result.extend(_walk_extent_node(f, child_data, 0, depth - 1))
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except OSError:
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pass
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return result
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def read_inode(f, sb, gdt_data, inum):
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"""Return raw inode block data and offset within it."""
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grp = (inum - 1) // sb['inodes_per_group']
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local_idx = (inum - 1) % sb['inodes_per_group']
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tbl_block = parse_gdt_entry(gdt_data, grp * sb['desc_size'], sb['desc_size'])
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byte_off = local_idx * sb['inode_size']
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blk_off = byte_off // BLOCK
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slot = byte_off % BLOCK
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data = read_at(f, (tbl_block + blk_off) * BLOCK, BLOCK)
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return data, slot
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def classify_inode(idata, slot):
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"""
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Returns 'deleted', 'orphaned', or 'active' based on inode fields.
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"""
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mode = struct.unpack_from('<H', idata, slot + 0)[0]
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links_count = struct.unpack_from('<H', idata, slot + 26)[0]
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dtime = struct.unpack_from('<I', idata, slot + 20)[0]
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flags = struct.unpack_from('<I', idata, slot + 32)[0]
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if dtime != 0 and links_count == 0:
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return 'deleted'
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if dtime != 0 and links_count > 0:
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# Inconsistent - probably corruption
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return 'corrupt'
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if dtime == 0 and links_count == 0:
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# Unallocated inode - should not appear in dir entries
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return 'unallocated'
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return 'active' # dtime=0, links_count>0 - normal live inode
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def read_dir_entries(f, sb, gdt_data, inum):
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"""Return dict of name -> (child_inum, ftype)."""
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idata, slot = read_inode(f, sb, gdt_data, inum)
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entries = {}
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for logical, phys in sorted(read_extent_tree_blocks(f, idata, slot)):
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try:
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bdata = read_at(f, phys * BLOCK, BLOCK)
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offset = 0
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while offset < BLOCK - 8:
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e_ino, rec_len, name_len, ftype = \
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struct.unpack_from('<IHBB', bdata, offset)
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if rec_len < 8 or offset + rec_len > BLOCK:
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break
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if e_ino != 0 and name_len > 0:
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name = bdata[offset+8:offset+8+name_len]\
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.decode('utf-8', errors='replace')
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entries[name] = (e_ino, ftype)
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offset += rec_len
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except OSError:
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pass
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return entries
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def dump_file(f, sb, gdt_data, inum, dest_path):
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"""Extract a regular file by inode to dest_path."""
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try:
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idata, slot = read_inode(f, sb, gdt_data, inum)
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size_lo = struct.unpack_from('<I', idata, slot + 4)[0]
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size_hi = struct.unpack_from('<I', idata, slot + 108)[0]
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size = size_lo | (size_hi << 32)
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flags = struct.unpack_from('<I', idata, slot + 32)[0]
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if flags & 0x10000000:
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# Inline data - stored in inode body after extent header
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inline = idata[slot+40:slot+40+size]
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with open(dest_path, 'wb') as out:
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out.write(inline)
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return True
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blocks = sorted(read_extent_tree_blocks(f, idata, slot))
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written = 0
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with open(dest_path, 'wb') as out:
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# Handle sparse files - fill holes with zeros
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for logical, phys in blocks:
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hole = logical * BLOCK
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if hole > written:
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out.seek(hole)
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written = hole
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remaining = size - written
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if remaining <= 0:
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break
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chunk = read_at(f, phys * BLOCK, BLOCK)
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out.write(chunk[:min(BLOCK, remaining)])
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written += min(BLOCK, remaining)
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out.truncate(size)
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return True
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except OSError:
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return False
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def dump_symlink(f, sb, gdt_data, inum, dest_path):
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try:
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idata, slot = read_inode(f, sb, gdt_data, inum)
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size = struct.unpack_from('<I', idata, slot + 4)[0]
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if size <= 60:
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target = idata[slot+40:slot+40+size].decode('utf-8', errors='replace')
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else:
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extents = read_extent_tree_blocks(f, idata, slot)
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if not extents:
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return False
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bdata = read_at(f, extents[0][1] * BLOCK, BLOCK)
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target = bdata[:size].decode('utf-8', errors='replace')
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# Strip null terminator, control characters, and anything after first null
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target = target.split('\x00')[0].strip()
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if not target:
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print(f" WARN empty symlink target for {dest_path}", file=sys.stderr)
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return False
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# Validate target looks like a path
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if any(ord(c) < 32 for c in target):
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print(f" WARN control chars in symlink target {dest_path!r} -> {target!r}",
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file=sys.stderr)
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return False
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if os.path.lexists(dest_path):
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return True # already exists from a previous run
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os.symlink(target, dest_path)
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return True
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except (OSError, IndexError) as e:
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print(f" WARN symlink {dest_path}: {e}", file=sys.stderr)
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return False
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# ── recursive dumper ─────────────────────────────────────────────────────────
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FTYPE_REG = 1
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FTYPE_DIR = 2
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FTYPE_SYM = 7
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def dump_tree(f, sb, gdt_data, inum, dest_dir, depth=0, visited=None):
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if visited is None:
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visited = set()
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if inum in visited:
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return
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visited.add(inum)
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try:
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entries = read_dir_entries(f, sb, gdt_data, inum)
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except Exception:
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return
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os.makedirs(dest_dir, exist_ok=True)
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for name, (child_inum, ftype) in entries.items():
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if name in ('.', '..'):
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continue
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safe_name = name.replace('/', '_').replace('\x00', '')
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dest = os.path.join(dest_dir, safe_name)
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try:
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# If ftype unknown, derive from inode mode
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if ftype == 0:
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idata, slot = read_inode(f, sb, gdt_data, child_inum)
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mode = struct.unpack_from('<H', idata, slot)[0]
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itype = mode & 0xF000
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if itype == 0x4000: ftype = FTYPE_DIR
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elif itype == 0x8000: ftype = FTYPE_REG
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elif itype == 0xA000: ftype = FTYPE_SYM
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if ftype == FTYPE_DIR:
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dump_tree(f, sb, gdt_data, child_inum, dest,
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depth+1, visited)
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elif ftype == FTYPE_REG:
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dump_file(f, sb, gdt_data, child_inum, dest)
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elif ftype == FTYPE_SYM:
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dump_symlink(f, sb, gdt_data, child_inum, dest)
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# ftype still 0 after mode check = special file, skip
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except Exception as e:
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print(f" WARN: {dest}: {e}", file=sys.stderr)
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