gitpython-developers
diff --git a/‎git/repo/base.py‎
Lines changed: 5 additions & 3 deletions b/‎git/repo/base.py‎
Lines changed: 5 additions & 3 deletions
diff --git a/‎git/repo/fun.py‎
Lines changed: 15 additions & 10 deletions b/‎git/repo/fun.py‎
Lines changed: 15 additions & 10 deletions
diff --git a/‎test/test_repo.py‎
Lines changed: 20 additions & 0 deletions b/‎test/test_repo.py‎
Lines changed: 20 additions & 0 deletions
@@ -356,9 +356,9 @@ def __init__(
             raise InvalidGitRepositoryError(epath)
         self.git_dir = git_dir
 
-        common_dir = os.getenv("GIT_COMMON_DIR")
-        if common_dir is not None:
-            self._common_dir = osp.abspath(common_dir)
+        common_dir_env = os.getenv("GIT_COMMON_DIR")
+        if common_dir_env is not None:
+            self._common_dir = osp.abspath(common_dir_env)
         else:
             try:
                 common_dir = (Path(self.git_dir) / "commondir").read_text().splitlines()[0].strip()
@@ -381,6 +381,8 @@ def __init__(
 
         self.working_dir: PathLike = self._working_tree_dir or self.common_dir
         self.git = self.GitCommandWrapperType(self.working_dir)
+        if common_dir_env is not None:
+            self.git.update_environment(GIT_DIR=os.fspath(self.git_dir), GIT_COMMON_DIR=os.fspath(self.common_dir))
 
         # Special handling, in special times.
         rootpath = osp.join(self.common_dir, "objects")
 
@@ -84,24 +84,29 @@ def is_git_dir(d: PathLike) -> bool:
                 )
 
         common_dir = os.getenv("GIT_COMMON_DIR")
+        if common_dir == "":
+            return False
         if common_dir is None:
             try:
-                common_dir = (Path(d) / "commondir").read_text().rstrip("\r\n")
+                common_dir = os.fsdecode((Path(d) / "commondir").read_bytes()).rstrip("\r\n")
             except FileNotFoundError:
                 common_dir = os.fspath(d)
             except OSError:
-                common_dir = ""
+                return False
             else:
-                common_dir = osp.realpath(osp.join(d, common_dir)) if common_dir else ""
-
-        object_dir = os.getenv("GIT_OBJECT_DIRECTORY") or osp.join(common_dir, "objects")
+                if not common_dir:
+                    return False
+                try:
+                    common_dir = osp.realpath(osp.join(d, common_dir))
+                except (OSError, ValueError):
+                    return False
+
+        object_dir = os.getenv("GIT_OBJECT_DIRECTORY")
+        if object_dir is None:
+            object_dir = osp.join(common_dir, "objects")
         if valid_head and osp.isdir(object_dir) and osp.isdir(osp.join(common_dir, "refs")):
             return True
-        if (
-            osp.isfile(osp.join(d, "gitdir"))
-            and osp.isfile(osp.join(d, "commondir"))
-            and osp.isfile(osp.join(d, "gitfile"))
-        ):
+        if osp.isfile(osp.join(d, "gitdir")) and osp.isfile(osp.join(d, "commondir")) and osp.isfile(headref):
             raise WorkTreeRepositoryUnsupported(d)
     return False
 
 
@@ -40,6 +40,7 @@
 from git.exc import UnsafeOptionError
 from git.exc import UnsafeProtocolError
 from git.exc import BadObject
+from git.exc import WorkTreeRepositoryUnsupported
 from git.repo.fun import touch
 from git.util import bin_to_hex, cwd, cygpath, join_path_native, rmfile, rmtree
 
@@ -158,6 +159,23 @@ def test_repo_discovery_rejects_invalid_metadata(self):
                 self.assertRaises(InvalidGitRepositoryError, Repo, path)
 
             (path / "HEAD").write_text("ref: refs/heads/main\n")
+
+            for contents in (b"", b"\xff"):
+                (path / "commondir").write_bytes(contents)
+                with cwd(path), self.subTest(metadata="commondir", contents=contents):
+                    self.assertRaises(InvalidGitRepositoryError, Repo, path)
+
+            (path / "gitdir").write_text("../worktree/.git\n")
+            (path / "commondir").write_text("missing\n")
+            with self.subTest(metadata="linked-worktree"):
+                self.assertRaises(WorkTreeRepositoryUnsupported, Repo, path)
+
+            (path / "gitdir").unlink()
+            (path / "commondir").unlink()
+            for variable in ("GIT_COMMON_DIR", "GIT_OBJECT_DIRECTORY"):
+                with mock.patch.dict(os.environ, {variable: ""}), self.subTest(metadata=variable):
+                    self.assertRaises(InvalidGitRepositoryError, Repo, path)
+
             (path / ".git").write_text("not a gitfile")
             with self.subTest(metadata=".git"):
                 self.assertRaises(InvalidGitRepositoryError, Repo, path)
@@ -180,6 +198,8 @@ def test_repo_discovery_uses_git_common_dir(self):
             assert osp.samefile(repo.common_dir, common_dir)
             assert osp.samefile(repo.odb.root_path(), common_dir / "objects")
             assert repo.bare
+            assert osp.samefile(repo.git.rev_parse("--absolute-git-dir"), git_dir)
+            assert osp.samefile(repo.git.rev_parse("--git-common-dir"), common_dir)
 
     @with_rw_repo("0.3.2.1")
     def test_repo_creation_from_different_paths(self, rw_repo):