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343
ext4lib.py
Executable file
343
ext4lib.py
Executable file
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#!/usr/bin/env python3
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"""
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EXT4 low-level filesystem primitives.
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All functions that need a file handle expect it open in 'rb' mode.
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"""
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import os, stat, struct, sys
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BLOCK = 4096
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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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ITYPE_REG = 0x8000
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ITYPE_DIR = 0x4000
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ITYPE_SYM = 0xA000
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# ── block I/O ─────────────────────────────────────────────────────────────────
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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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# ── superblock / GDT ──────────────────────────────────────────────────────────
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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['feature_incompat'] = struct.unpack_from('<I', data, 96)[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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"""Return inode table block number from a group descriptor entry."""
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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 load_fs(f, backup_sb_block):
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"""Read superblock and full GDT from backup location.
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Returns (sb, gdt_data, num_groups).
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Raises AssertionError if the magic number is wrong.
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"""
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sb_data = read_at(f, backup_sb_block * BLOCK, 1024)
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sb = parse_superblock(sb_data)
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assert sb['magic'] == 0xef53, f"Bad superblock magic: {sb['magic']:#x}"
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num_groups = (sb['blocks_count'] + sb['blocks_per_group'] - 1) // sb['blocks_per_group']
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gdt_data = read_at(f, (backup_sb_block + 1) * BLOCK, num_groups * sb['desc_size'])
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return sb, gdt_data, num_groups
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# ── extent tree ───────────────────────────────────────────────────────────────
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def read_extent_tree_blocks(f, data, inode_offset):
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"""Return sorted list of (logical_block, phys_block) pairs for an inode.
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data – the BLOCK-sized buffer that contains the inode
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inode_offset – byte offset of the inode within data
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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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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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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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# ── inode ─────────────────────────────────────────────────────────────────────
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def read_inode(f, sb, gdt_data, inum):
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"""Return (block_data, offset_within_block) for the given inode number."""
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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 parse_inode_full(data, offset, sb):
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"""Parse all fields from a raw inode buffer.
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Returns a dict, or None if the buffer is too short.
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"""
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if len(data) - offset < 128:
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return None
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mode = struct.unpack_from('<H', data, offset + 0)[0]
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uid_lo = struct.unpack_from('<H', data, offset + 2)[0]
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size_lo = struct.unpack_from('<I', data, offset + 4)[0]
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atime = struct.unpack_from('<I', data, offset + 8)[0]
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ctime = struct.unpack_from('<I', data, offset + 12)[0]
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mtime = struct.unpack_from('<I', data, offset + 16)[0]
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dtime = struct.unpack_from('<I', data, offset + 20)[0]
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gid_lo = struct.unpack_from('<H', data, offset + 24)[0]
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links = struct.unpack_from('<H', data, offset + 26)[0]
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flags = struct.unpack_from('<I', data, offset + 32)[0]
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uid_hi, gid_hi = struct.unpack_from('<HH', data, offset + 120)
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size_hi = 0
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if sb.get('inode_size', 128) >= 256 and len(data) - offset >= 164:
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size_hi = struct.unpack_from('<I', data, offset + 108)[0]
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return {
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'mode': mode,
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'type': mode & 0xF000,
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'uid': uid_lo | (uid_hi << 16),
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'gid': gid_lo | (gid_hi << 16),
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'size': size_lo | (size_hi << 32),
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'atime': atime,
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'ctime': ctime,
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'mtime': mtime,
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'dtime': dtime,
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'links': links,
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'flags': flags,
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}
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def classify_inode(idata, slot):
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"""Return 'active', 'deleted', 'corrupt', or 'unallocated'."""
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links = 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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if dtime != 0 and links == 0:
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return 'deleted'
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if dtime != 0 and links > 0:
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return 'corrupt'
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if dtime == 0 and links == 0:
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return 'unallocated'
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return 'active'
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def get_inode_meta(idata, slot, sb):
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"""Return (permissions, uid, gid, atime, mtime) from a raw inode buffer."""
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mode = struct.unpack_from('<H', idata, slot + 0)[0]
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uid_lo = struct.unpack_from('<H', idata, slot + 2)[0]
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gid_lo = struct.unpack_from('<H', idata, slot + 24)[0]
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atime = struct.unpack_from('<I', idata, slot + 8)[0]
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mtime = struct.unpack_from('<I', idata, slot + 16)[0]
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uid_hi, gid_hi = struct.unpack_from('<HH', idata, slot + 120)
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uid = uid_lo | (uid_hi << 16)
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gid = gid_lo | (gid_hi << 16)
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if sb.get('inode_size', 128) >= 256:
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atime_extra = struct.unpack_from('<I', idata, slot + 132)[0]
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mtime_extra = struct.unpack_from('<I', idata, slot + 140)[0]
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atime |= (atime_extra & 0x3) << 32
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mtime |= (mtime_extra & 0x3) << 32
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return stat.S_IMODE(mode), uid, gid, atime, mtime
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# ── directory entries ─────────────────────────────────────────────────────────
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def read_dir_entries_raw(f, idata, inode_offset):
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"""Read directory entries given raw inode data (already in memory).
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Returns dict of name -> (child_inum, ftype).
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"""
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entries = {}
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for _logical, phys in sorted(read_extent_tree_blocks(f, idata, inode_offset)):
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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 = 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].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 read_dir_entries(f, sb, gdt_data, inum):
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"""Read directory entries for inode inum. Returns dict of name -> (child_inum, ftype)."""
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idata, slot = read_inode(f, sb, gdt_data, inum)
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return read_dir_entries_raw(f, idata, slot)
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# ── file extraction ───────────────────────────────────────────────────────────
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def dump_file(f, sb, gdt_data, inum, dest_path):
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"""Extract a regular file by inode number to dest_path. Returns True on success."""
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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 = 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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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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"""Create a symlink at dest_path from the symlink inode. Returns True on success."""
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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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target = target.split('\x00')[0].strip()
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if not target or any(ord(c) < 32 for c in target):
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print(f" WARN invalid symlink target for {dest_path!r}: {target!r}", 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
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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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def dump_tree(f, sb, gdt_data, inum, dest_dir, db=None, depth=0, visited=None):
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"""Recursively extract a directory tree.
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If db is provided (an ext4db connection), directory entries are read from
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the database instead of from disk — much faster for subsequent runs.
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"""
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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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if db is not None:
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import ext4db
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entries = ext4db.get_dir_entries(db, inum)
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else:
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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 == 0:
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idata, slot = read_inode(f, sb, gdt_data, child_inum)
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itype = struct.unpack_from('<H', idata, slot)[0] & 0xF000
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if itype == ITYPE_DIR: ftype = FTYPE_DIR
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elif itype == ITYPE_REG: ftype = FTYPE_REG
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elif itype == ITYPE_SYM: ftype = FTYPE_SYM
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if ftype == FTYPE_DIR:
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dump_tree(f, sb, gdt_data, child_inum, dest, db=db,
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depth=depth + 1, visited=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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except Exception as e:
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print(f" WARN {dest}: {e}", file=sys.stderr)
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