[PATCH v3 16/26] submodule--helper: fix "reference" leak is "module_clone_data"

[Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>]

Fix leaks in the "reference" member of "struct module_clone_data" that
have been with us since 31224cbdc72 (clone: recursive and reference
option triggers submodule alternates, 2016-08-17) and
8c8195e9c3e (submodule--helper: introduce add-clone subcommand,
2021-07-10).

Those commits added an xstrdup()'d member of the
STRING_LIST_INIT_NODUP'd "struct string_list". We need to free()
those, but not the ones we get from argv, let's make use of the "util"
member, if it has a pointer it's the pointer we'll need to free,
otherwise it'll be NULL (i.e. from argv).

To fix this create a a module_clone_data_release() function to go with
the MODULE_CLONE_DATA_INIT added in a98b02c1128 (submodule--helper:
refactor module_clone(), 2021-07-10). We only need to add it to
add_submodule() to fix the leak, but let's add it to module_clone() as
well for consistency.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 builtin/submodule--helper.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index fe490c8d44d..80c1c1d4918 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1584,6 +1584,11 @@ struct module_clone_data {
 	.single_branch = -1, \
 }
 
+static void module_clone_data_release(struct module_clone_data *cd)
+{
+	string_list_clear(&cd->reference, 1);
+}
+
 struct submodule_alternate_setup {
 	const char *submodule_name;
 	enum SUBMODULE_ALTERNATE_ERROR_MODE {
@@ -1636,7 +1641,9 @@ static int add_possible_reference_from_superproject(
 
 		sm_alternate = compute_alternate_path(sb.buf, &err);
 		if (sm_alternate) {
-			string_list_append(sas->reference, xstrdup(sb.buf));
+			char *p = strbuf_detach(&sb, NULL);
+
+			string_list_append(sas->reference, p)->util = p;
 			free(sm_alternate);
 		} else {
 			switch (sas->error_mode) {
@@ -1873,6 +1880,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 
 	clone_submodule(&clone_data, &clone_data.reference);
 	list_objects_filter_release(&filter_options);
+	module_clone_data_release(&clone_data);
 	return 0;
 }
 
@@ -3117,6 +3125,7 @@ static int add_submodule(const struct add_data *add_data)
 {
 	char *submod_gitdir_path;
 	struct module_clone_data clone_data = MODULE_CLONE_DATA_INIT;
+	int ret = -1;
 
 	/* perhaps the path already exists and is already a git repo, else clone it */
 	if (is_directory(add_data->sm_path)) {
@@ -3171,15 +3180,17 @@ static int add_submodule(const struct add_data *add_data)
 		clone_data.url = add_data->realrepo;
 		clone_data.quiet = add_data->quiet;
 		clone_data.progress = add_data->progress;
-		if (add_data->reference_path)
-			string_list_append(&clone_data.reference,
-					   xstrdup(add_data->reference_path));
+		if (add_data->reference_path) {
+			char *p = xstrdup(add_data->reference_path);
+
+			string_list_append(&clone_data.reference, p)->util = p;
+		}
 		clone_data.dissociate = add_data->dissociate;
 		if (add_data->depth >= 0)
 			clone_data.depth = xstrfmt("%d", add_data->depth);
 
 		if (clone_submodule(&clone_data, &clone_data.reference))
-			return -1;
+			goto cleanup;
 
 		prepare_submodule_repo_env(&cp.env);
 		cp.git_cmd = 1;
@@ -3198,7 +3209,10 @@ static int add_submodule(const struct add_data *add_data)
 		if (run_command(&cp))
 			die(_("unable to checkout submodule '%s'"), add_data->sm_path);
 	}
-	return 0;
+	ret = 0;
+cleanup:
+	module_clone_data_release(&clone_data);
+	return ret;
 }
 
 static int config_submodule_in_gitmodules(const char *name, const char *var, const char *value)
-- 
2.37.1.1095.g0bd6f54ba8a