submodules: submodule paths must not contain symlinks

When creating a submodule path, we must be careful not to follow
symbolic links. Otherwise we may follow a symbolic link pointing to
a gitdir (which are valid symbolic links!) e.g. while cloning.

On case-insensitive filesystems, however, we blindly replace a directory
that has been created as part of the `clone` operation with a symlink
when the path to the latter differs only in case from the former's path.

Let's simply avoid this situation by expecting not ever having to
overwrite any existing file/directory/symlink upon cloning. That way, we
won't even replace a directory that we just created.

This addresses CVE-2024-32002.

Reported-by: Filip Hejsek <filip.hejsek@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

1 files changed, 48 insertions, 0 deletions

diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index f094e3d7f3..63c24f7f7c 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -1179,4 +1179,52 @@ test_expect_success 'submodule update --recursive skip submodules with strategy=
 	test_cmp expect.err actual.err
 '
 
+test_expect_success CASE_INSENSITIVE_FS,SYMLINKS \
+	'submodule paths must not follow symlinks' '
+
+	# This is only needed because we want to run this in a self-contained
+	# test without having to spin up an HTTP server; However, it would not
+	# be needed in a real-world scenario where the submodule is simply
+	# hosted on a public site.
+	test_config_global protocol.file.allow always &&
+
+	# Make sure that Git tries to use symlinks on Windows
+	test_config_global core.symlinks true &&
+
+	tell_tale_path="$PWD/tell.tale" &&
+	git init hook &&
+	(
+		cd hook &&
+		mkdir -p y/hooks &&
+		write_script y/hooks/post-checkout <<-EOF &&
+		echo HOOK-RUN >&2
+		echo hook-run >"$tell_tale_path"
+		EOF
+		git add y/hooks/post-checkout &&
+		test_tick &&
+		git commit -m post-checkout
+	) &&
+
+	hook_repo_path="$(pwd)/hook" &&
+	git init captain &&
+	(
+		cd captain &&
+		git submodule add --name x/y "$hook_repo_path" A/modules/x &&
+		test_tick &&
+		git commit -m add-submodule &&
+
+		printf .git >dotgit.txt &&
+		git hash-object -w --stdin <dotgit.txt >dot-git.hash &&
+		printf "120000 %s 0\ta\n" "$(cat dot-git.hash)" >index.info &&
+		git update-index --index-info <index.info &&
+		test_tick &&
+		git commit -m add-symlink
+	) &&
+
+	test_path_is_missing "$tell_tale_path" &&
+	test_must_fail git clone --recursive captain hooked 2>err &&
+	grep "directory not empty" err &&
+	test_path_is_missing "$tell_tale_path"
+'
+
 test_done