keyfile: ensure array lengths are always initialized

Several callers access the length output argument, expecting
it to be zero also on failure. That is a bug, because glib does
not guarantee that.

Fix that by making a stronger promise from our wrappers: the output
argument should also be set on failure.

Also ensure that calls to g_keyfile_get_groups() and
g_keyfile_get_keys() don't rely on the length output to be valid,
when the function call fails.

Actually, these issues were not severe because:

- `g_key_file_get_*_list()`'s implementation always sets the output length
  even on failure (undocumented).
- `g_key_file_get_groups()` cannot fail and always set the length.
- `g_key_file_get_keys()` is called under circumstances where it won't
  fail.

Still, be explicit about it.

1 files changed, 10 insertions, 5 deletions

diff --git a/libnm-core/nm-keyfile.c b/libnm-core/nm-keyfile.c
index 161b2fd501..b3c4cdd53b 100644
--- a/libnm-core/nm-keyfile.c
+++ b/libnm-core/nm-keyfile.c
@@ -2723,6 +2723,8 @@ read_setting (KeyfileReaderInfo *info)
 		gsize i, n_keys;
 
 		keys = g_key_file_get_keys (info->keyfile, info->group, &n_keys, NULL);
+		if (!keys)
+			n_keys = 0;
 		if (n_keys > 0) {
 			GHashTable *h = _nm_setting_gendata_hash (setting, TRUE);
 
@@ -2798,15 +2800,15 @@ static void
 read_vpn_secrets (KeyfileReaderInfo *info, NMSettingVpn *s_vpn)
 {
 	gs_strfreev char **keys = NULL;
-	char **iter;
+	gsize i, n_keys;
 
-	keys = nm_keyfile_plugin_kf_get_keys (info->keyfile, NM_KEYFILE_GROUP_VPN_SECRETS, NULL, NULL);
-	for (iter = keys; *iter; iter++) {
+	keys = nm_keyfile_plugin_kf_get_keys (info->keyfile, NM_KEYFILE_GROUP_VPN_SECRETS, &n_keys, NULL);
+	for (i = 0; i < n_keys; i++) {
 		char *secret;
 
-		secret = nm_keyfile_plugin_kf_get_string (info->keyfile, NM_KEYFILE_GROUP_VPN_SECRETS, *iter, NULL);
+		secret = nm_keyfile_plugin_kf_get_string (info->keyfile, NM_KEYFILE_GROUP_VPN_SECRETS, keys[i], NULL);
 		if (secret) {
-			nm_setting_vpn_add_secret (s_vpn, *iter, secret);
+			nm_setting_vpn_add_secret (s_vpn, keys[i], secret);
 			g_free (secret);
 		}
 	}
@@ -2896,6 +2898,9 @@ nm_keyfile_read (GKeyFile *keyfile,
 	info.user_data = user_data;
 
 	groups = g_key_file_get_groups (keyfile, &length);
+	if (!groups)
+		length = 0;
+
 	for (i = 0; i < length; i++) {
 		/* Only read out secrets when needed */
 		if (!strcmp (groups[i], NM_KEYFILE_GROUP_VPN_SECRETS)) {