commit: fix leaking parents when calling commit_tree_extended()

When creating commits via `commit_tree_extended()`, the caller passes in
a string list of parents. This call implicitly transfers ownership of
that list to the function, which is quite surprising to begin with. But
to make matters worse, `commit_tree_extended()` doesn't even bother to
free the list of parents in error cases. The result is a memory leak,
and one that the caller cannot fix by themselves because they do not
know whether parts of the string list have already been released.

Refactor the code such that callers can keep ownership of the list of
parents, which is getting indicated by parameter being a constant
pointer now. Free the lists at the calling site and add a common exit
path to those sites as required.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -1718,6 +1718,7 @@ static void do_commit(const struct am_state *state)
 
 	run_hooks("post-applypatch");
 
+	free_commit_list(parents);
 	strbuf_release(&sb);
 }
 

builtin/commit-tree.c

@@ -111,6 +111,7 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 			N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 		OPT_END()
 	};
+	int ret;
 
 	git_config(git_default_config, NULL);
 
@@ -132,11 +133,15 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 
 	if (commit_tree(buffer.buf, buffer.len, &tree_oid, parents, &commit_oid,
 			NULL, sign_commit)) {
-		strbuf_release(&buffer);
-		return 1;
+		ret = 1;
+		goto out;
 	}
 
 	printf("%s\n", oid_to_hex(&commit_oid));
+	ret = 0;
+
+out:
+	free_commit_list(parents);
 	strbuf_release(&buffer);
-	return 0;
+	return ret;
 }

builtin/commit.c

@@ -1848,7 +1848,6 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		rollback_index_files();
 		die(_("failed to write commit object"));
 	}
-	free_commit_extra_headers(extra);
 
 	if (update_head_with_reflog(current_head, &oid, reflog_msg, &sb,
 				    &err)) {
@@ -1890,6 +1889,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	apply_autostash_ref(the_repository, "MERGE_AUTOSTASH");
 
 cleanup:
+	free_commit_extra_headers(extra);
+	free_commit_list(parents);
 	strbuf_release(&author_ident);
 	strbuf_release(&err);
 	strbuf_release(&sb);

builtin/merge.c

@@ -895,7 +895,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 {
 	struct object_id result_tree, result_commit;
-	struct commit_list *parents, **pptr = &parents;
+	struct commit_list *parents = NULL, **pptr = &parents;
 
 	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET,
 					 SKIP_IF_UNCHANGED, 0, NULL, NULL,
@@ -911,7 +911,9 @@ static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 			&result_commit, NULL, sign_commit))
 		die(_("failed to write commit object"));
 	finish(head, remoteheads, &result_commit, "In-index merge");
+
 	remove_merge_branch_state(the_repository);
+	free_commit_list(parents);
 	return 0;
 }
 
@@ -937,8 +939,10 @@ static int finish_automerge(struct commit *head,
 		die(_("failed to write commit object"));
 	strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 	finish(head, remoteheads, &result_commit, buf.buf);
+
 	strbuf_release(&buf);
 	remove_merge_branch_state(the_repository);
+	free_commit_list(parents);
 	return 0;
 }
 

builtin/replay.c

@@ -52,11 +52,11 @@ static struct commit *create_commit(struct tree *tree,
 				    struct commit *parent)
 {
 	struct object_id ret;
-	struct object *obj;
+	struct object *obj = NULL;
 	struct commit_list *parents = NULL;
 	char *author;
 	char *sign_commit = NULL; /* FIXME: cli users might want to sign again */
-	struct commit_extra_header *extra;
+	struct commit_extra_header *extra = NULL;
 	struct strbuf msg = STRBUF_INIT;
 	const char *out_enc = get_commit_output_encoding();
 	const char *message = repo_logmsg_reencode(the_repository, based_on,
@@ -73,12 +73,16 @@ static struct commit *create_commit(struct tree *tree,
 	if (commit_tree_extended(msg.buf, msg.len, &tree->object.oid, parents,
 				 &ret, author, NULL, sign_commit, extra)) {
 		error(_("failed to write commit object"));
-		return NULL;
+		goto out;
 	}
-	free(author);
-	strbuf_release(&msg);
 
 	obj = parse_object(the_repository, &ret);
+
+out:
+	free_commit_extra_headers(extra);
+	free_commit_list(parents);
+	strbuf_release(&msg);
+	free(author);
 	return (struct commit *)obj;
 }
 

builtin/stash.c

@@ -1416,6 +1416,9 @@ static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_b
 		goto done;
 	}
 
+	free_commit_list(parents);
+	parents = NULL;
+
 	if (include_untracked) {
 		if (save_untracked_files(info, &msg, untracked_files)) {
 			if (!quiet)
@@ -1461,11 +1464,6 @@ static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_b
 	else
 		strbuf_insertf(stash_msg_buf, 0, "On %s: ", branch_name);
 
-	/*
-	 * `parents` will be empty after calling `commit_tree()`, so there is
-	 * no need to call `free_commit_list()`
-	 */
-	parents = NULL;
 	if (untracked_commit_option)
 		commit_list_insert(lookup_commit(the_repository,
 						 &info->u_commit),
@@ -1487,6 +1485,7 @@ done:
 	strbuf_release(&commit_tree_label);
 	strbuf_release(&msg);
 	strbuf_release(&untracked_files);
+	free_commit_list(parents);
 	return ret;
 }