Reject submodule checkout paths outside the repository

GHSA-59cr-6r3x-644w identifies that submodule update paths could reach filesystem operations without the containment check already used by add and move.

Add a regression that proves update rejects a parent-directory checkout path before cloning, and override Submodule.abspath to apply the shared _to_relative_path guard for every filesystem consumer.

Git baseline: git.git read-cache.c verify_path_internal() rejects invalid index paths, covered for parent traversal by t/t9300-fast-import.sh.

Validation: .venv/bin/python -m pytest test/test_submodule.py -q; pre-commit run --files git/objects/submodule/base.py test/test_submodule.py; mypy git/objects/submodule/base.py; git diff --check.

Author: codex

git/objects/submodule/base.py

@@ -414,6 +414,11 @@ def _to_relative_path(cls, parent_repo: "Repo", path: PathLike) -> PathLike:
 
         return path
 
+    @property
+    def abspath(self) -> PathLike:
+        self._to_relative_path(self.repo, self.path)
+        return super().abspath
+
     @classmethod
     def _write_git_file_and_module_config(cls, working_tree_dir: PathLike, module_abspath: PathLike) -> None:
         """Write a ``.git`` file containing a (preferably) relative path to the actual

test/test_submodule.py

@@ -1369,6 +1369,21 @@ class Repo:
             osp.join(Repo.working_tree_dir + "-other", "module"),
         )
 
+    @with_rw_directory
+    def test_update_rejects_checkout_path_outside_parent(self, rwdir):
+        parent = git.Repo.init(osp.join(rwdir, "parent"))
+        submodule = Submodule(
+            parent,
+            Submodule.NULL_BIN_SHA,
+            name="module",
+            path=osp.join("..", "outside"),
+            url="unused",
+        )
+
+        with mock.patch.object(Submodule, "_clone_repo", side_effect=AssertionError("clone attempted")):
+            with pytest.raises(ValueError, match="is not in repository"):
+                submodule.update(init=True)
+
     @skipUnless(sys.platform == "win32", "Specifically for Windows.")
     @with_rw_directory
     def test_to_relative_path_windows_path_kinds(self, rwdir):