config: avoid cloning string during nm_config_data_get_connection_default() et al.

NMConfigData is immutable and with the previous commit are the strings
already cached internally. There is no need to clone it.

Of course, the callers must not assume that the string stays alive after
a config reload (SIGHUP), where the NMConfigData might change. So they
are not always alive, but long enough for all callers to avoid cloning
the string.

6 files changed, 128 insertions, 172 deletions

diff --git a/src/core/devices/nm-device.c b/src/core/devices/nm-device.c
index f43646845a..1c70ecb328 100644
--- a/src/core/devices/nm-device.c
+++ b/src/core/devices/nm-device.c
@@ -820,8 +820,7 @@ _prop_get_connection_stable_id(NMDevice *         self,
      * Especially with ${RANDOM} stable-id we want to generate *one* configuration
      * for each activation. */
     if (G_UNLIKELY(!priv->current_stable_id)) {
-        gs_free char *       default_id = NULL;
-        gs_free char *       generated  = NULL;
+        gs_free char *       generated = NULL;
         NMUtilsStableType    stable_type;
         NMSettingConnection *s_con;
         gboolean             hwaddr_is_fake;
@@ -834,11 +833,10 @@ _prop_get_connection_stable_id(NMDevice *         self,
         stable_id = nm_setting_connection_get_stable_id(s_con);
 
         if (!stable_id) {
-            default_id =
+            stable_id =
                 nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
                                                       NM_CON_DEFAULT("connection.stable-id"),
                                                       self);
-            stable_id = default_id;
         }
 
         uuid = nm_connection_get_uuid(connection);
@@ -897,7 +895,6 @@ _prop_get_ipv6_dhcp_duid(NMDevice *    self,
 {
     NMSettingIPConfig *s_ip6;
     const char *       duid;
-    gs_free char *     duid_default = NULL;
     const char *       duid_error;
     GBytes *           duid_out;
     gboolean           duid_enforce = TRUE;
@@ -910,10 +907,9 @@ _prop_get_ipv6_dhcp_duid(NMDevice *    self,
     duid  = nm_setting_ip6_config_get_dhcp_duid(NM_SETTING_IP6_CONFIG(s_ip6));
 
     if (!duid) {
-        duid_default = nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
-                                                             NM_CON_DEFAULT("ipv6.dhcp-duid"),
-                                                             self);
-        duid         = duid_default;
+        duid = nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
+                                                     NM_CON_DEFAULT("ipv6.dhcp-duid"),
+                                                     self);
         if (!duid)
             duid = "lease";
     }
@@ -1390,7 +1386,6 @@ _prop_get_ipvx_dhcp_iaid(NMDevice *    self,
     const int          IS_IPv4 = NM_IS_IPv4(addr_family);
     NMSettingIPConfig *s_ip;
     const char *       iaid_str;
-    gs_free char *     iaid_str_free = NULL;
     guint32            iaid;
     const char *       iface;
     const char *       fail_reason;
@@ -1399,11 +1394,10 @@ _prop_get_ipvx_dhcp_iaid(NMDevice *    self,
     s_ip     = nm_connection_get_setting_ip_config(connection, addr_family);
     iaid_str = nm_setting_ip_config_get_dhcp_iaid(s_ip);
     if (!iaid_str) {
-        iaid_str_free = nm_config_data_get_connection_default(
-            NM_CONFIG_GET_DATA,
-            IS_IPv4 ? NM_CON_DEFAULT("ipv4.dhcp-iaid") : NM_CON_DEFAULT("ipv6.dhcp-iaid"),
-            self);
-        iaid_str = iaid_str_free;
+        iaid_str = nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
+                                                         IS_IPv4 ? NM_CON_DEFAULT("ipv4.dhcp-iaid")
+                                                                 : NM_CON_DEFAULT("ipv6.dhcp-iaid"),
+                                                         self);
         if (!iaid_str) {
             iaid_str    = NM_IAID_IFNAME;
             is_explicit = FALSE;
@@ -1560,12 +1554,10 @@ _prop_get_ipvx_dhcp_hostname_flags(NMDevice *self, int addr_family)
 }
 
 static const char *
-_prop_get_connection_mud_url(NMDevice *self, NMSettingConnection *s_con, char **out_mud_url)
+_prop_get_connection_mud_url(NMDevice *self, NMSettingConnection *s_con)
 {
-    const char *  mud_url;
-    gs_free char *s = NULL;
-
-    nm_assert(out_mud_url && !*out_mud_url);
+    const char *mud_url;
+    const char *s;
 
     mud_url = nm_setting_connection_get_mud_url(s_con);
 
@@ -1582,7 +1574,7 @@ _prop_get_connection_mud_url(NMDevice *self, NMSettingConnection *s_con, char **
         if (nm_streq(s, NM_CONNECTION_MUD_URL_NONE))
             return NULL;
         if (nm_sd_http_url_is_valid_https(s))
-            return (*out_mud_url = g_steal_pointer(&s));
+            return s;
     }
 
     return NULL;
@@ -1593,7 +1585,6 @@ _prop_get_ipv4_dhcp_client_id(NMDevice *self, NMConnection *connection, GBytes *
 {
     NMSettingIPConfig *s_ip4;
     const char *       client_id;
-    gs_free char *     client_id_default = NULL;
     guint8 *           client_id_buf;
     const char *       fail_reason;
     guint8             hwaddr_bin_buf[_NM_UTILS_HWADDR_LEN_MAX];
@@ -1607,13 +1598,12 @@ _prop_get_ipv4_dhcp_client_id(NMDevice *self, NMConnection *connection, GBytes *
     client_id = nm_setting_ip4_config_get_dhcp_client_id(NM_SETTING_IP4_CONFIG(s_ip4));
 
     if (!client_id) {
-        client_id_default =
-            nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
-                                                  NM_CON_DEFAULT("ipv4.dhcp-client-id"),
-                                                  self);
-        if (client_id_default && client_id_default[0]) {
+        client_id = nm_config_data_get_connection_default(NM_CONFIG_GET_DATA,
+                                                          NM_CON_DEFAULT("ipv4.dhcp-client-id"),
+                                                          self);
+        if (client_id && !client_id[0]) {
             /* a non-empty client-id is always valid, see nm_dhcp_utils_client_id_string_to_bytes().  */
-            client_id = client_id_default;
+            client_id = NULL;
         }
     }
 
@@ -1745,8 +1735,7 @@ out_good:
 static GBytes *
 _prop_get_ipv4_dhcp_vendor_class_identifier(NMDevice *self, NMSettingIP4Config *s_ip4)
 {
-    gs_free char *config_data_prop = NULL;
-    gs_free char *to_free          = NULL;
+    gs_free char *to_free = NULL;
     const char *  conn_prop;
     GBytes *      bytes = NULL;
     const char *  bin;
@@ -1756,13 +1745,13 @@ _prop_get_ipv4_dhcp_vendor_class_identifier(NMDevice *self, NMSettingIP4Config *
 
     if (!conn_prop) {
         /* set in NetworkManager.conf ? */
-        config_data_prop = nm_config_data_get_connection_default(
+        conn_prop = nm_config_data_get_connection_default(
             NM_CONFIG_GET_DATA,
             NM_CON_DEFAULT("ipv4.dhcp-vendor-class-identifier"),
             self);
 
-        if (config_data_prop && nm_utils_validate_dhcp4_vendor_class_id(config_data_prop, NULL))
-            conn_prop = config_data_prop;
+        if (conn_prop && !nm_utils_validate_dhcp4_vendor_class_id(conn_prop, NULL))
+            conn_prop = NULL;
     }
 
     if (conn_prop) {
@@ -1828,16 +1817,11 @@ _prop_get_ipv6_ip6_privacy(NMDevice *self)
 }
 
 static const char *
-_prop_get_x_cloned_mac_address(NMDevice *    self,
-                               NMConnection *connection,
-                               gboolean      is_wifi,
-                               char **       out_addr)
+_prop_get_x_cloned_mac_address(NMDevice *self, NMConnection *connection, gboolean is_wifi)
 {
     NMSetting * setting;
     const char *addr = NULL;
 
-    nm_assert(out_addr && !*out_addr);
-
     setting = nm_connection_get_setting(connection,
                                         is_wifi ? NM_TYPE_SETTING_WIRELESS : NM_TYPE_SETTING_WIRED);
     if (setting) {
@@ -1846,7 +1830,7 @@ _prop_get_x_cloned_mac_address(NMDevice *    self,
     }
 
     if (!addr) {
-        gs_free char *a = NULL;
+        const char *a;
 
         a = nm_config_data_get_connection_default(
             NM_CONFIG_GET_DATA,
@@ -1861,36 +1845,28 @@ _prop_get_x_cloned_mac_address(NMDevice *    self,
                 NMSettingMacRandomization v;
 
                 /* for backward compatibility, read the deprecated wifi.mac-address-randomization setting. */
-                a = nm_config_data_get_connection_default(
+                v = nm_config_data_get_connection_default_int64(
                     NM_CONFIG_GET_DATA,
                     NM_CON_DEFAULT("wifi.mac-address-randomization"),
-                    self);
-                v = _nm_utils_ascii_str_to_int64(a,
-                                                 10,
-                                                 NM_SETTING_MAC_RANDOMIZATION_DEFAULT,
-                                                 NM_SETTING_MAC_RANDOMIZATION_ALWAYS,
-                                                 NM_SETTING_MAC_RANDOMIZATION_DEFAULT);
+                    self,
+                    NM_SETTING_MAC_RANDOMIZATION_DEFAULT,
+                    NM_SETTING_MAC_RANDOMIZATION_ALWAYS,
+                    NM_SETTING_MAC_RANDOMIZATION_DEFAULT);
                 if (v == NM_SETTING_MAC_RANDOMIZATION_ALWAYS)
                     addr = NM_CLONED_MAC_RANDOM;
             }
         } else if (NM_CLONED_MAC_IS_SPECIAL(a) || nm_utils_hwaddr_valid(a, ETH_ALEN))
-            addr = *out_addr = g_steal_pointer(&a);
+            addr = a;
     }
 
     return addr;
 }
 
 static const char *
-_prop_get_x_generate_mac_address_mask(NMDevice *    self,
-                                      NMConnection *connection,
-                                      gboolean      is_wifi,
-                                      char **       out_value)
+_prop_get_x_generate_mac_address_mask(NMDevice *self, NMConnection *connection, gboolean is_wifi)
 {
     NMSetting * setting;
-    const char *value = NULL;
-    char *      a;
-
-    nm_assert(out_value && !*out_value);
+    const char *value;
 
     setting = nm_connection_get_setting(connection,
                                         is_wifi ? NM_TYPE_SETTING_WIRELESS : NM_TYPE_SETTING_WIRED);
@@ -1903,15 +1879,11 @@ _prop_get_x_generate_mac_address_mask(NMDevice *    self,
             return value;
     }
 
-    a = nm_config_data_get_connection_default(
+    return nm_config_data_get_connection_default(
         NM_CONFIG_GET_DATA,
         is_wifi ? NM_CON_DEFAULT("wifi.generate-mac-address-mask")
                 : NM_CON_DEFAULT("ethernet.generate-mac-address-mask"),
         self);
-    if (!a)
-        return NULL;
-    *out_value = a;
-    return a;
 }
 
 /*****************************************************************************/
@@ -9417,7 +9389,6 @@ dhcp4_start(NMDevice *self)
     gs_unref_bytes GBytes *hwaddr                  = NULL;
     gs_unref_bytes GBytes *bcast_hwaddr            = NULL;
     gs_unref_bytes GBytes *client_id               = NULL;
-    gs_free char *         mud_url_free            = NULL;
     NMConnection *         connection;
     NMSettingConnection *  s_con;
     GError *               error = NULL;
@@ -9477,7 +9448,7 @@ dhcp4_start(NMDevice *self)
         nm_setting_ip_config_get_dhcp_hostname(s_ip4),
         nm_setting_ip4_config_get_dhcp_fqdn(NM_SETTING_IP4_CONFIG(s_ip4)),
         _prop_get_ipvx_dhcp_hostname_flags(self, AF_INET),
-        _prop_get_connection_mud_url(self, s_con, &mud_url_free),
+        _prop_get_connection_mud_url(self, s_con),
         client_id,
         _prop_get_ipvx_dhcp_timeout(self, AF_INET),
         _device_get_dhcp_anycast_address(self),
@@ -9881,8 +9852,7 @@ dhcp6_start_with_link_ready(NMDevice *self, NMConnection *connection)
     gs_unref_bytes GBytes *     duid         = NULL;
     gboolean                    enforce_duid = FALSE;
     const NMPlatformLink *      pllink;
-    gs_free char *              mud_url_free = NULL;
-    GError *                    error        = NULL;
+    GError *                    error = NULL;
     guint32                     iaid;
     gboolean                    iaid_explicit;
     NMSettingConnection *       s_con;
@@ -9927,7 +9897,7 @@ dhcp6_start_with_link_ready(NMDevice *self, NMConnection *connection)
         nm_setting_ip_config_get_dhcp_send_hostname(s_ip6),
         nm_setting_ip_config_get_dhcp_hostname(s_ip6),
         _prop_get_ipvx_dhcp_hostname_flags(self, AF_INET6),
-        _prop_get_connection_mud_url(self, s_con, &mud_url_free),
+        _prop_get_connection_mud_url(self, s_con),
         duid,
         enforce_duid,
         iaid,
@@ -17277,14 +17247,13 @@ _hw_addr_get_cloned(NMDevice *    self,
                     gboolean *    preserve,
                     char **       hwaddr,
                     HwAddrType *  hwaddr_type,
-                    char **       hwaddr_detail,
+                    const char ** hwaddr_detail,
                     GError **     error)
 {
     NMDevicePrivate *priv;
-    gs_free char *   addr_setting_free             = NULL;
-    gs_free char *   hw_addr_generated             = NULL;
-    gs_free char *   generate_mac_address_mask_tmp = NULL;
-    const char *     addr, *addr_setting;
+    gs_free char *   hw_addr_generated = NULL;
+    const char *     addr;
+    const char *     addr_setting;
     char *           addr_out;
     HwAddrType       type_out;
 
@@ -17297,15 +17266,16 @@ _hw_addr_get_cloned(NMDevice *    self,
     if (!connection)
         g_return_val_if_reached(FALSE);
 
-    addr = addr_setting =
-        _prop_get_x_cloned_mac_address(self, connection, is_wifi, &addr_setting_free);
+    addr_setting = _prop_get_x_cloned_mac_address(self, connection, is_wifi);
+
+    addr = addr_setting;
 
     if (nm_streq(addr, NM_CLONED_MAC_PRESERVE)) {
         /* "preserve" means to reset the initial MAC address. */
         NM_SET_OUT(preserve, TRUE);
         NM_SET_OUT(hwaddr, NULL);
         NM_SET_OUT(hwaddr_type, HW_ADDR_TYPE_UNSET);
-        NM_SET_OUT(hwaddr_detail, g_steal_pointer(&addr_setting_free) ?: g_strdup(addr_setting));
+        NM_SET_OUT(hwaddr_detail, addr_setting);
         return TRUE;
     }
 
@@ -17318,8 +17288,7 @@ _hw_addr_get_cloned(NMDevice *    self,
             NM_SET_OUT(preserve, TRUE);
             NM_SET_OUT(hwaddr, NULL);
             NM_SET_OUT(hwaddr_type, HW_ADDR_TYPE_UNSET);
-            NM_SET_OUT(hwaddr_detail,
-                       g_steal_pointer(&addr_setting_free) ?: g_strdup(addr_setting));
+            NM_SET_OUT(hwaddr_detail, addr_setting);
             return TRUE;
         } else if (!addr) {
             g_set_error_literal(error,
@@ -17339,10 +17308,7 @@ _hw_addr_get_cloned(NMDevice *    self,
         }
         hw_addr_generated = nm_utils_hw_addr_gen_random_eth(
             nm_device_get_initial_hw_address(self),
-            _prop_get_x_generate_mac_address_mask(self,
-                                                  connection,
-                                                  is_wifi,
-                                                  &generate_mac_address_mask_tmp));
+            _prop_get_x_generate_mac_address_mask(self, connection, is_wifi));
         if (!hw_addr_generated) {
             g_set_error(error,
                         NM_DEVICE_ERROR,
@@ -17370,10 +17336,7 @@ _hw_addr_get_cloned(NMDevice *    self,
             stable_id,
             nm_device_get_ip_iface(self),
             nm_device_get_initial_hw_address(self),
-            _prop_get_x_generate_mac_address_mask(self,
-                                                  connection,
-                                                  is_wifi,
-                                                  &generate_mac_address_mask_tmp));
+            _prop_get_x_generate_mac_address_mask(self, connection, is_wifi));
         if (!hw_addr_generated) {
             g_set_error(error,
                         NM_DEVICE_ERROR,
@@ -17397,7 +17360,7 @@ _hw_addr_get_cloned(NMDevice *    self,
     NM_SET_OUT(preserve, FALSE);
     NM_SET_OUT(hwaddr, addr_out);
     NM_SET_OUT(hwaddr_type, type_out);
-    NM_SET_OUT(hwaddr_detail, g_steal_pointer(&addr_setting_free) ?: g_strdup(addr_setting));
+    NM_SET_OUT(hwaddr_detail, addr_setting);
     return TRUE;
 out_no_action:
     NM_SET_OUT(preserve, FALSE);
@@ -17427,7 +17390,7 @@ nm_device_hw_addr_set_cloned(NMDevice *self, NMConnection *connection, gboolean
     NMDevicePrivate *priv;
     gboolean         preserve   = FALSE;
     gs_free char *   hwaddr     = NULL;
-    gs_free char *   detail     = NULL;
+    const char *     detail     = NULL;
     HwAddrType       type       = HW_ADDR_TYPE_UNSET;
     gs_free_error GError *error = NULL;
 
diff --git a/src/core/devices/wifi/nm-device-wifi.c b/src/core/devices/wifi/nm-device-wifi.c
index dd52186d82..fca2fde515 100644
--- a/src/core/devices/wifi/nm-device-wifi.c
+++ b/src/core/devices/wifi/nm-device-wifi.c
@@ -1382,8 +1382,8 @@ _hw_addr_set_scanning(NMDeviceWifi *self, gboolean do_reset)
     now = nm_utils_get_monotonic_timestamp_sec();
 
     if (now >= priv->hw_addr_scan_expire) {
-        gs_free char *generate_mac_address_mask = NULL;
-        gs_free char *hw_addr_scan              = NULL;
+        gs_free char *hw_addr_scan = NULL;
+        const char *  generate_mac_address_mask;
 
         /* the random MAC address for scanning expires after a while.
          *
diff --git a/src/core/devices/wifi/nm-wifi-factory.c b/src/core/devices/wifi/nm-wifi-factory.c
index c7be7ab8cb..d2269c74ef 100644
--- a/src/core/devices/wifi/nm-wifi-factory.c
+++ b/src/core/devices/wifi/nm-wifi-factory.c
@@ -74,7 +74,8 @@ create_device(NMDeviceFactory *     factory,
               NMConnection *        connection,
               gboolean *            out_ignore)
 {
-    gs_free char *backend = NULL;
+    gs_free char *backend_free = NULL;
+    const char *  backend;
 
     g_return_val_if_fail(iface != NULL, NULL);
     g_return_val_if_fail(plink != NULL, NULL);
@@ -89,7 +90,7 @@ create_device(NMDeviceFactory *     factory,
                                                          plink,
                                                          "wifi",
                                                          NULL);
-    nm_strstrip(backend);
+    backend = nm_strstrip_avoid_copy_a(300, backend, &backend_free);
 
     nm_log_dbg(LOGD_PLATFORM | LOGD_WIFI,
                "(%s) config: backend is %s%s%s%s",
diff --git a/src/core/nm-config-data.c b/src/core/nm-config-data.c
index f6667e926d..e127ea23bb 100644
--- a/src/core/nm-config-data.c
+++ b/src/core/nm-config-data.c
@@ -359,9 +359,9 @@ nm_config_data_get_iwd_config_path(const NMConfigData *self)
 gboolean
 nm_config_data_get_ignore_carrier(const NMConfigData *self, NMDevice *device)
 {
-    gs_free char *value = NULL;
-    gboolean      has_match;
-    int           m;
+    const char *value;
+    gboolean    has_match;
+    int         m;
 
     g_return_val_if_fail(NM_IS_CONFIG_DATA(self), FALSE);
     g_return_val_if_fail(NM_IS_DEVICE(device), FALSE);
@@ -1397,7 +1397,7 @@ _match_section_infos_lookup(const MatchSectionInfo *match_section_infos,
                             NMDevice *              device,
                             const NMPlatformLink *  pllink,
                             const char *            match_device_type,
-                            char **                 out_value)
+                            const char **           out_value)
 {
     const char *match_dhcp_plugin;
 
@@ -1436,7 +1436,7 @@ _match_section_infos_lookup(const MatchSectionInfo *match_section_infos,
             match = TRUE;
 
         if (match) {
-            *out_value = g_strdup(value);
+            *out_value = value;
             return match_section_infos;
         }
     }
@@ -1446,7 +1446,7 @@ out:
     return NULL;
 }
 
-char *
+const char *
 nm_config_data_get_device_config(const NMConfigData *self,
                                  const char *        property,
                                  NMDevice *          device,
@@ -1454,7 +1454,7 @@ nm_config_data_get_device_config(const NMConfigData *self,
 {
     const NMConfigDataPrivate *priv;
     const MatchSectionInfo *   connection_info;
-    char *                     value = NULL;
+    const char *               value;
 
     NM_SET_OUT(has_match, FALSE);
 
@@ -1474,7 +1474,7 @@ nm_config_data_get_device_config(const NMConfigData *self,
     return value;
 }
 
-char *
+const char *
 nm_config_data_get_device_config_by_pllink(const NMConfigData *  self,
                                            const char *          property,
                                            const NMPlatformLink *pllink,
@@ -1483,7 +1483,7 @@ nm_config_data_get_device_config_by_pllink(const NMConfigData *  self,
 {
     const NMConfigDataPrivate *priv;
     const MatchSectionInfo *   connection_info;
-    char *                     value = NULL;
+    const char *               value;
 
     g_return_val_if_fail(self, NULL);
     g_return_val_if_fail(property && *property, NULL);
@@ -1508,8 +1508,8 @@ nm_config_data_get_device_config_boolean(const NMConfigData *self,
                                          int                 val_no_match,
                                          int                 val_invalid)
 {
-    gs_free char *value = NULL;
-    gboolean      has_match;
+    const char *value;
+    gboolean    has_match;
 
     value = nm_config_data_get_device_config(self, property, device, &has_match);
     if (!has_match)
@@ -1527,8 +1527,8 @@ nm_config_data_get_device_config_int64(const NMConfigData *self,
                                        gint64              val_no_match,
                                        gint64              val_invalid)
 {
-    gs_free char *value = NULL;
-    gboolean      has_match;
+    const char *value;
+    gboolean    has_match;
 
     value = nm_config_data_get_device_config(self, property, device, &has_match);
     if (!has_match) {
@@ -1538,13 +1538,13 @@ nm_config_data_get_device_config_int64(const NMConfigData *self,
     return _nm_utils_ascii_str_to_int64(value, base, min, max, val_invalid);
 }
 
-char *
+const char *
 nm_config_data_get_connection_default(const NMConfigData *self,
                                       const char *        property,
                                       NMDevice *          device)
 {
     const NMConfigDataPrivate *priv;
-    char *                     value = NULL;
+    const char *               value;
 
     g_return_val_if_fail(self, NULL);
     g_return_val_if_fail(property && *property, NULL);
@@ -1583,7 +1583,7 @@ nm_config_data_get_connection_default_int64(const NMConfigData *self,
                                             gint64              max,
                                             gint64              fallback)
 {
-    gs_free char *value = NULL;
+    const char *value;
 
     value = nm_config_data_get_connection_default(self, property, device);
     return _nm_utils_ascii_str_to_int64(value, 10, min, max, fallback);
diff --git a/src/core/nm-config-data.h b/src/core/nm-config-data.h
index 0d133b8c57..42d69a8b92 100644
--- a/src/core/nm-config-data.h
+++ b/src/core/nm-config-data.h
@@ -207,9 +207,9 @@ extern const char *__stop_connection_defaults[];
         name;                                                                               \
     })
 
-char *nm_config_data_get_connection_default(const NMConfigData *self,
-                                            const char *        property,
-                                            NMDevice *          device);
+const char *nm_config_data_get_connection_default(const NMConfigData *self,
+                                                  const char *        property,
+                                                  NMDevice *          device);
 
 gint64 nm_config_data_get_connection_default_int64(const NMConfigData *self,
                                                    const char *        property,
@@ -218,16 +218,16 @@ gint64 nm_config_data_get_connection_default_int64(const NMConfigData *self,
                                                    gint64              max,
                                                    gint64              fallback);
 
-char *nm_config_data_get_device_config(const NMConfigData *self,
-                                       const char *        property,
-                                       NMDevice *          device,
-                                       gboolean *          has_match);
+const char *nm_config_data_get_device_config(const NMConfigData *self,
+                                             const char *        property,
+                                             NMDevice *          device,
+                                             gboolean *          has_match);
 
-char *nm_config_data_get_device_config_by_pllink(const NMConfigData *  self,
-                                                 const char *          property,
-                                                 const NMPlatformLink *pllink,
-                                                 const char *          match_device_type,
-                                                 gboolean *            has_match);
+const char *nm_config_data_get_device_config_by_pllink(const NMConfigData *  self,
+                                                       const char *          property,
+                                                       const NMPlatformLink *pllink,
+                                                       const char *          match_device_type,
+                                                       gboolean *            has_match);
 
 gboolean nm_config_data_get_device_config_boolean(const NMConfigData *self,
                                                   const char *        property,
diff --git a/src/core/tests/config/test-config.c b/src/core/tests/config/test-config.c
index 3bb148152b..6794fbf6cb 100644
--- a/src/core/tests/config/test-config.c
+++ b/src/core/tests/config/test-config.c
@@ -151,6 +151,7 @@ test_config_simple(void)
     gs_unref_object NMConfig *config  = NULL;
     gs_strfreev char **       plugins = NULL;
     char *                    value;
+    const char *              cvalue;
     gs_unref_object NMDevice *dev50 = nm_test_device_new("00:00:00:00:00:50");
     gs_unref_object NMDevice *dev51 = nm_test_device_new("00:00:00:00:00:51");
     gs_unref_object NMDevice *dev52 = nm_test_device_new("00:00:00:00:00:52");
@@ -206,59 +207,50 @@ test_config_simple(void)
     g_assert_cmpstr(value, ==, "51");
     g_free(value);
 
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv6.route-metric",
-                                                  NULL);
-    g_assert_cmpstr(value, ==, NULL);
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.route-metric",
-                                                  NULL);
-    g_assert_cmpstr(value, ==, "50");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.route-metric",
-                                                  dev50);
-    g_assert_cmpstr(value, ==, "50");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.route-metric",
-                                                  dev51);
-    g_assert_cmpstr(value, ==, "51");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.route-metric",
-                                                  dev52);
-    g_assert_cmpstr(value, ==, "52");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ethernet.mtu",
-                                                  dev51);
-    g_assert_cmpstr(value, ==, "9000");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ethernet.mtu",
-                                                  dev50);
-    g_assert_cmpstr(value, ==, "1400");
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.dns-priority",
-                                                  dev51);
-    g_assert_cmpstr(value, ==, NULL);
-    g_free(value);
-
-    value = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
-                                                  "ipv4.dns-priority",
-                                                  dev50);
-    g_assert_cmpstr(value, ==, "60");
-    g_free(value);
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv6.route-metric",
+                                                   NULL);
+    g_assert_cmpstr(cvalue, ==, NULL);
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.route-metric",
+                                                   NULL);
+    g_assert_cmpstr(cvalue, ==, "50");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.route-metric",
+                                                   dev50);
+    g_assert_cmpstr(cvalue, ==, "50");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.route-metric",
+                                                   dev51);
+    g_assert_cmpstr(cvalue, ==, "51");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.route-metric",
+                                                   dev52);
+    g_assert_cmpstr(cvalue, ==, "52");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ethernet.mtu",
+                                                   dev51);
+    g_assert_cmpstr(cvalue, ==, "9000");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ethernet.mtu",
+                                                   dev50);
+    g_assert_cmpstr(cvalue, ==, "1400");
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.dns-priority",
+                                                   dev51);
+    g_assert_cmpstr(cvalue, ==, NULL);
+
+    cvalue = nm_config_data_get_connection_default(nm_config_get_data_orig(config),
+                                                   "ipv4.dns-priority",
+                                                   dev50);
+    g_assert_cmpstr(cvalue, ==, "60");
 }
 
 static void
@@ -616,7 +608,7 @@ test_config_confdir(void)
 #define ASSERT_GET_CONN_DEFAULT(xconfig, xname, xvalue)                             \
     G_STMT_START                                                                    \
     {                                                                               \
-        gs_free char *_value =                                                      \
+        const char *_value =                                                        \
             nm_config_data_get_connection_default(nm_config_get_data_orig(xconfig), \
                                                   (xname),                          \
                                                   NULL);                            \