libnm: fix regression serializing empty "cloned-mac-address"

For "cloned-mac-address", the empty string "" is an invalid
value that is rejected by verify().

Commit 8eed671 changed how the property is serialized to D-Bus.
Before, it was serialized using _nm_utils_hwaddr_to_dbus().
For invalid or empty addresses, this would not serialize the
value on D-Bus (or before commit 76aa6f8e0, it would create
a bogus value with no array elements).

With commit 8eed671, the cloned-mac-address gets also serialized
as "assigned-mac-address" via _nm_utils_hwaddr_cloned_data_synth(),
which would pass on invalid strings that the server would then reject.

That breaks for example nmtui. Try editing a connection with
"cloned-mac-address" set to NULL. Note, as long as you don't edit
the cloned MAC address in nmtui, you can save the modification.
Once you start modifying the entry, you can no longer set an empty
MAC address as the server now receives the invalid empty string.
Thus, the "OK" button fails with
   Unable to save connection:
   802-3-ethernet.cloned-mac-address:
   is not a valid MAC address
It also means, nmtui cannot modify the "cloned-mac-address" field to
become empty.

Fix that problem at various places by coercing "" to NULL.

Fixes: 8eed67122c58540360b617eb42d5df8328e21b5d

https://bugzilla.redhat.com/show_bug.cgi?id=1372799

2 files changed, 19 insertions, 3 deletions

diff --git a/clients/tui/nmt-mac-entry.c b/clients/tui/nmt-mac-entry.c
index da7f55fac1..b954d2e0c9 100644
--- a/clients/tui/nmt-mac-entry.c
+++ b/clients/tui/nmt-mac-entry.c
@@ -201,7 +201,8 @@ nmt_mac_entry_get_property (GObject    *object,
 		g_value_set_int (value, priv->mac_length);
 		break;
 	case PROP_MAC_ADDRESS:
-		g_value_set_string (value, nmt_newt_entry_get_text (NMT_NEWT_ENTRY (object)));
+		g_value_set_string (value,
+		                    nm_str_not_empty (nmt_newt_entry_get_text (NMT_NEWT_ENTRY (object))));
 		break;
 	case PROP_ENTRY_TYPE:
 		g_value_set_int (value, priv->entry_type);
diff --git a/libnm-core/nm-utils.c b/libnm-core/nm-utils.c
index a31a91906f..df75d56557 100644
--- a/libnm-core/nm-utils.c
+++ b/libnm-core/nm-utils.c
@@ -3425,7 +3425,22 @@ _nm_utils_hwaddr_cloned_data_synth (NMSetting *setting,
 	              "cloned-mac-address",
 	              &addr,
 	              NULL);
-	return addr ? g_variant_new_string (addr) : NULL;
+
+	/* Before introducing the extended "cloned-mac-address" (and its D-Bus
+	 * field "assigned-mac-address"), libnm's _nm_utils_hwaddr_to_dbus()
+	 * would drop invalid values as it was unable to serialize them.
+	 *
+	 * Now, we would like to send invalid values as "assigned-mac-address"
+	 * over D-Bus and let the server reject them.
+	 *
+	 * However, clients used to set the cloned-mac-address property
+	 * to "" and it just worked as the value was not serialized in
+	 * an ill form.
+	 *
+	 * To preserve that behavior, seralize "" as NULL.
+	 */
+
+	return addr && addr[0] ? g_variant_new_string (addr) : NULL;
 }
 
 gboolean
@@ -3443,7 +3458,7 @@ _nm_utils_hwaddr_cloned_data_set (NMSetting *setting,
 
 	g_object_set (setting,
 	              "cloned-mac-address",
-	              g_variant_get_string (value, NULL),
+	              nm_str_not_empty (g_variant_get_string (value, NULL)),
 	              NULL);
 	return TRUE;
 }