Merge main and fix encrypted backup extraction

tests/ios_backup/test_decrypt.py

@@ -0,0 +1,125 @@
+# Mobile Verification Toolkit (MVT)
+# Copyright (c) 2021-2023 The MVT Authors.
+# Use of this software is governed by the MVT License 1.1 that can be found at
+#   https://license.mvt.re/1.1/
+
+from pathlib import Path
+
+from Crypto.Cipher import AES
+
+from mvt.ios.decrypt import DecryptBackup, MVTEncryptedBackup
+
+
+def _encrypted_file(backup_path, file_id, key, plaintext):
+    padding_length = AES.block_size - (len(plaintext) % AES.block_size)
+    padded = plaintext + bytes([padding_length]) * padding_length
+    encrypted = AES.new(key, AES.MODE_CBC, iv=b"\x00" * AES.block_size).encrypt(
+        padded
+    )
+    source_path = backup_path / file_id[:2] / file_id
+    source_path.parent.mkdir(parents=True)
+    source_path.write_bytes(encrypted)
+
+
+def test_extract_file_by_id_preserves_bytes_with_wrong_manifest_size(
+    mocker, tmp_path
+):
+    file_id = "ab" + "1" * 38
+    plaintext = b"complete decrypted content"
+    inner_key = b"k" * 32
+    _encrypted_file(tmp_path, file_id, inner_key, plaintext)
+
+    file_plist = mocker.Mock(
+        encryption_key=b"wrapped-key",
+        protection_class=1,
+        filesize=1,
+        mtime=None,
+    )
+    mocker.patch("mvt.ios.decrypt.FilePlist", return_value=file_plist)
+
+    backup = MVTEncryptedBackup(
+        backup_directory=str(tmp_path), derived_key=b"d" * 32
+    )
+    mocker.patch.object(backup, "_read_and_unlock_keybag", return_value=True)
+    backup._keybag = mocker.Mock()
+    backup._keybag.unwrapKeyForClass.return_value = inner_key
+    streaming_decrypt = mocker.spy(backup, "_decrypt_file_to_disk")
+    output_path = tmp_path / "output"
+
+    backup.extract_file_by_id(
+        file_id=file_id,
+        file_bplist=b"plist",
+        output_filename=str(output_path),
+    )
+
+    assert output_path.read_bytes() == plaintext
+    streaming_decrypt.assert_called_once()
+
+
+def test_extract_file_by_id_copies_unencrypted_files(mocker, tmp_path):
+    file_id = "cd" + "2" * 38
+    source_path = tmp_path / file_id[:2] / file_id
+    source_path.parent.mkdir(parents=True)
+    source_path.write_bytes(b"plain content")
+
+    file_plist = mocker.Mock(encryption_key=None)
+    mocker.patch("mvt.ios.decrypt.FilePlist", return_value=file_plist)
+    backup = MVTEncryptedBackup(
+        backup_directory=str(tmp_path), derived_key=b"d" * 32
+    )
+    mocker.patch.object(backup, "_read_and_unlock_keybag", return_value=True)
+    output_path = tmp_path / "output"
+
+    backup.extract_file_by_id(
+        file_id=file_id,
+        file_bplist=b"plist",
+        output_filename=str(output_path),
+    )
+
+    assert output_path.read_bytes() == b"plain content"
+
+
+def test_process_backup_rejects_unsafe_file_ids_and_destinations(mocker, tmp_path):
+    backup_path = tmp_path / "backup"
+    destination = tmp_path / "destination"
+    outside = tmp_path / "outside"
+    backup_path.mkdir()
+    destination.mkdir()
+    outside.mkdir()
+
+    safe_file_id = "ef" + "3" * 38
+    unsafe_file_id = "../../outside-file"
+    symlink_file_id = "ab" + "4" * 38
+    for file_id in (safe_file_id, symlink_file_id):
+        source_path = backup_path / file_id[:2] / file_id
+        source_path.parent.mkdir(parents=True, exist_ok=True)
+        source_path.write_bytes(b"encrypted")
+    (destination / "ab").symlink_to(outside, target_is_directory=True)
+
+    cursor = mocker.MagicMock()
+    cursor.__iter__.return_value = iter(
+        [
+            (safe_file_id, "Domain", "safe", b"plist"),
+            (unsafe_file_id, "Domain", "unsafe", b"plist"),
+            (symlink_file_id, "Domain", "symlink", b"plist"),
+        ]
+    )
+    cursor_context = mocker.MagicMock()
+    cursor_context.__enter__.return_value = cursor
+
+    backup = mocker.MagicMock()
+    backup.manifest_db_cursor.return_value = cursor_context
+
+    def extract_file_by_id(*, output_filename, **kwargs):
+        Path(output_filename).write_bytes(b"decrypted")
+
+    backup.extract_file_by_id.side_effect = extract_file_by_id
+    decryptor = DecryptBackup(str(backup_path), str(destination))
+    decryptor._backup = backup
+
+    decryptor.process_backup()
+
+    assert (destination / safe_file_id[:2] / safe_file_id).read_bytes() == b"decrypted"
+    assert not (outside / symlink_file_id).exists()
+    backup.extract_file_by_id.assert_called_once()
+    assert backup.extract_file_by_id.call_args.kwargs["file_id"] == safe_file_id