Brooklyn Nicholson
110ecd238e
Profile export/import owns the only hardened tar handling in the tree: GNU-format writing (PAX fractional mtimes make macOS Archive Utility throw "Error 94"), plus an extractor that rejects absolute paths, `..` components, and non-regular members. Kanban board transfer needs exactly that, and a second copy is how the weaker of two extractors eventually ships. Move the four helpers to hermes_cli/archive_safe and point profiles at them; no behavior change beyond dropping a provably-unreachable fallback in the root-listing helper, whose condition is a strict subset of the comprehension above it.
131 lines
4.9 KiB
Python
131 lines
4.9 KiB
Python
"""Safe ``tar.gz`` primitives shared by the profile and kanban transfer paths.
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Both ``hermes profile export|import`` and ``hermes kanban export|import``
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ship a directory to another machine and unpack whatever comes back. The
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unpack side is the dangerous half: a hand-crafted archive can carry
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``../`` members, absolute paths, symlinks, or device nodes, any of which
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turn an import into an arbitrary-write primitive. These helpers are the
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one place that logic lives so a second transfer surface can't ship a
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second, subtly weaker extractor.
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The writer is deliberately not :func:`shutil.make_archive`: that emits
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PAX (Python's tarfile default since 3.8), whose fractional-mtime records
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macOS Archive Utility rejects — double-clicking an exported profile threw
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"Error 94 - Bad message." GNU format keeps long paths working (longlink
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extensions) and stays integer-mtime, so Finder, bsdtar, and gnutar all
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extract it.
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"""
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from __future__ import annotations
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import os
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import shutil
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import tarfile
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from pathlib import Path, PurePosixPath, PureWindowsPath
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def normalize_archive_parts(member_name: str) -> list[str]:
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"""Return safe path parts for an archive member, or raise.
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Rejects absolute paths (POSIX and Windows, including drive letters),
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empty names, and any ``..`` component. Backslashes are folded to
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``/`` first so a Windows-authored archive can't smuggle a separator
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past the POSIX parse.
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"""
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normalized_name = member_name.replace("\\", "/")
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posix_path = PurePosixPath(normalized_name)
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windows_path = PureWindowsPath(member_name)
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if (
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not normalized_name
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or posix_path.is_absolute()
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or windows_path.is_absolute()
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or windows_path.drive
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):
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raise ValueError(f"Unsafe archive member path: {member_name}")
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parts = [part for part in posix_path.parts if part not in {"", "."}]
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if not parts or any(part == ".." for part in parts):
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raise ValueError(f"Unsafe archive member path: {member_name}")
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return parts
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def make_targz(base: str, root_dir: str, base_dir: str) -> str:
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"""Create ``<base>.tar.gz`` of ``root_dir/base_dir`` in GNU tar format."""
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archive_path = f"{base}.tar.gz"
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with tarfile.open(archive_path, "w:gz", format=tarfile.GNU_FORMAT) as tf:
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tf.add(str(Path(root_dir) / base_dir), arcname=base_dir)
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return archive_path
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def safe_extract_targz(archive: Path, destination: Path) -> None:
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"""Extract ``archive`` into ``destination`` without path escapes or links.
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Only directories and regular files are extracted; symlinks, hardlinks,
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and device nodes raise rather than being silently skipped, so a
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tampered archive fails the import instead of landing a partial tree.
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"""
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with tarfile.open(archive, "r:gz") as tf:
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for member in tf.getmembers():
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parts = normalize_archive_parts(member.name)
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target = destination.joinpath(*parts)
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if member.isdir():
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target.mkdir(parents=True, exist_ok=True)
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continue
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if not member.isfile():
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raise ValueError(
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f"Unsupported archive member type: {member.name}"
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)
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target.parent.mkdir(parents=True, exist_ok=True)
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extracted = tf.extractfile(member)
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if extracted is None:
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raise ValueError(f"Cannot read archive member: {member.name}")
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with extracted, open(target, "wb") as dst:
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shutil.copyfileobj(extracted, dst)
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try:
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os.chmod(target, member.mode & 0o777)
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except OSError:
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pass
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def archive_root_dirs(archive: Path) -> set[str]:
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"""Return the archive's top-level directory names.
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Transfer archives carry exactly one root directory, which names the
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thing being imported. Inspecting the archive before extraction lets
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the caller resolve the target name (and refuse a malformed archive)
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without first mutating a live tree.
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"""
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with tarfile.open(archive, "r:gz") as tf:
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return {
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parts[0]
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for member in tf.getmembers()
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for parts in [normalize_archive_parts(member.name)]
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if len(parts) > 1 or member.isdir()
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}
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def copy_regular_files(src: Path, dst: Path) -> int:
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"""Copy the regular files under ``src`` into ``dst``, skipping symlinks.
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Used on the *export* side so a symlink planted in an attachments or
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logs tree can't pull an arbitrary file into the archive. Returns the
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number of files copied; a missing ``src`` copies nothing.
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"""
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if not src.is_dir():
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return 0
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copied = 0
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for entry in sorted(src.rglob("*")):
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if entry.is_symlink() or not entry.is_file():
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continue
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target = dst / entry.relative_to(src)
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target.parent.mkdir(parents=True, exist_ok=True)
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shutil.copyfile(entry, target)
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copied += 1
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return copied
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