policy: detect if the hostname was changed outside NetworkManager

When updating the hostname we can now detect if someone else changed
the hostname: if so, search for hostname candidates in the dhcp
configuration but avoid to fallback to the hostname saved when NM
started or querying dns for a reverse lookup of the current IP.

1 files changed, 74 insertions, 15 deletions

diff --git a/src/nm-policy.c b/src/nm-policy.c
index 5b04e7f231..1a489d4445 100644
--- a/src/nm-policy.c
+++ b/src/nm-policy.c
@@ -87,6 +87,8 @@ typedef struct {
 
 	char *orig_hostname; /* hostname at NM start time */
 	char *cur_hostname;  /* hostname we want to assign */
+	char *last_hostname; /* last hostname NM set (to detect if someone else changed it in the meanwhile) */
+	gboolean changing_hostname; /* hostname set operation still in progress */
 
 	GArray *ip6_prefix_delegations; /* pool of ip6 prefixes delegated to all devices */
 } NMPolicyPrivate;
@@ -412,6 +414,8 @@ settings_set_hostname_cb (const char *hostname,
                           gboolean result,
                           gpointer user_data)
 {
+	NMPolicy *self = NM_POLICY (user_data);
+	NMPolicyPrivate *priv = NM_POLICY_GET_PRIVATE (self);
 	int ret = 0;
 
 	if (!result) {
@@ -426,8 +430,10 @@ settings_set_hostname_cb (const char *hostname,
 		}
 	}
 
+	priv->changing_hostname = FALSE;
 	if (!ret)
 		nm_dispatcher_call_hostname (NULL, NULL, NULL);
+	g_object_unref (self);
 }
 
 #define HOST_NAME_BUFSIZE (HOST_NAME_MAX + 2)
@@ -440,6 +446,15 @@ _get_hostname (NMPolicy *self, char **hostname)
 
 	g_assert (hostname && *hostname == NULL);
 
+	/* If there is an in-progress hostname change, return
+	 * the last hostname set as would be set soon...
+	 */
+	if (priv->changing_hostname) {
+		_LOGT (LOGD_DNS, "gethostname: \"%s\" (last on set)", priv->last_hostname);
+		*hostname = g_strdup (priv->last_hostname);
+		return *hostname;
+	}
+
 	/* try to get the hostname via dbus... */
 	if (nm_settings_get_transient_hostname (priv->settings, hostname)) {
 		_LOGT (LOGD_DNS, "gethostname: \"%s\" (from dbus)", *hostname);
@@ -521,6 +536,11 @@ _set_hostname (NMPolicy *self,
 		return;
 	}
 
+	/* Keep track of the last set hostname */
+	g_free (priv->last_hostname);
+	priv->last_hostname = g_strdup (name);
+	priv->changing_hostname = TRUE;
+
 	_LOGI (LOGD_DNS, "sethostname: '%s' (%s)", name, msg);
 
 	/* Ask NMSettings to update the transient hostname using its
@@ -528,7 +548,7 @@ _set_hostname (NMPolicy *self,
 	nm_settings_set_transient_hostname (priv->settings,
 	                                    name,
 	                                    settings_set_hostname_cb,
-	                                    NULL);
+	                                    g_object_ref (self));
 }
 
 static void
@@ -563,19 +583,43 @@ update_system_hostname (NMPolicy *self, NMDevice *best4, NMDevice *best6)
 {
 	NMPolicyPrivate *priv = NM_POLICY_GET_PRIVATE (self);
 	char *configured_hostname = NULL;
+	gs_free char *temp_hostname = NULL;
 	const char *dhcp_hostname, *p;
 	NMIP4Config *ip4_config;
 	NMIP6Config *ip6_config;
+	gboolean external_hostname = FALSE;
 
 	g_return_if_fail (self != NULL);
 
 	nm_clear_g_cancellable (&priv->lookup_cancellable);
 
+	/* Check if the hostname was set externally to NM, so that in that case
+	 * we can avoid to fallback to the one we got when we started.
+	 * Consider "not specific" hostnames as equal. */
+	if (   _get_hostname (self, &temp_hostname)
+	    && !nm_streq0 (temp_hostname, priv->last_hostname)
+	    && (   nm_utils_is_specific_hostname (temp_hostname)
+	        || nm_utils_is_specific_hostname (priv->last_hostname))) {
+		external_hostname = TRUE;
+		_LOGI (LOGD_DNS, "current hostname was changed outside NetworkManager: '%s'",
+		       temp_hostname);
+
+		if (!nm_streq0 (temp_hostname, priv->orig_hostname)) {
+			/* Update original (fallback) hostname */
+			g_free (priv->orig_hostname);
+			if (nm_utils_is_specific_hostname (temp_hostname)) {
+				priv->orig_hostname = temp_hostname;
+				temp_hostname = NULL;
+			} else
+				priv->orig_hostname = NULL;
+		}
+	}
+
 	/* Hostname precedence order:
 	 *
 	 * 1) a configured hostname (from settings)
 	 * 2) automatic hostname from the default device's config (DHCP, VPN, etc)
-	 * 3) the original hostname when NM started
+	 * 3) the last hostname set outside NM
 	 * 4) reverse-DNS of the best device's IPv4 address
 	 *
 	 */
@@ -595,14 +639,6 @@ update_system_hostname (NMPolicy *self, NMDevice *best4, NMDevice *best6)
 	if (!best6)
 		best6 = get_best_ip6_device (self, TRUE);
 
-	if (!best4 && !best6) {
-		/* No best device; fall back to original hostname or if there wasn't
-		 * one, 'localhost.localdomain'
-		 */
-		_set_hostname (self, priv->orig_hostname, "no default device");
-		return;
-	}
-
 	if (best4) {
 		NMDhcp4Config *dhcp4_config;
 
@@ -643,8 +679,20 @@ update_system_hostname (NMPolicy *self, NMDevice *best4, NMDevice *best6)
 		}
 	}
 
-	/* If no automatically-configured hostname, try using the hostname from
-	 * when NM started up.
+	/* If an hostname was set outside NetworkManager keep it */
+	if (external_hostname)
+		return;
+
+	if (!best4 && !best6) {
+		/* No best device; fall back to the last hostname set externally
+		 * to NM or if there wasn't one, 'localhost.localdomain'
+		 */
+		_set_hostname (self, priv->orig_hostname, "no default device");
+		return;
+	}
+
+	/* If no automatically-configured hostname, try using the last hostname
+	 * set externally to NM
 	 */
 	if (priv->orig_hostname) {
 		_set_hostname (self, priv->orig_hostname, "from system startup");
@@ -2004,6 +2052,15 @@ dns_config_changed (NMDnsManager *dns_manager, gpointer user_data)
 	/* Re-start the hostname lookup thread if we don't have hostname yet. */
 	if (priv->lookup_addr) {
 		char *str = NULL;
+		gs_free char *hostname = NULL;
+
+		/* Check if the hostname was externally set */
+		if (   _get_hostname (self, &hostname)
+		    && nm_utils_is_specific_hostname (hostname)
+		    && !nm_streq0 (hostname, priv->last_hostname)) {
+			g_clear_object (&priv->lookup_addr);
+			return;
+		}
 
 		_LOGD (LOGD_DNS, "restarting reverse-lookup thread for address %s",
 		       (str = g_inet_address_to_string (priv->lookup_addr)));
@@ -2213,11 +2270,12 @@ constructed (GObject *object)
 
 	/* Grab hostname on startup and use that if nothing provides one */
 	if (_get_hostname (self, &hostname)) {
+		/* init last_hostname */
+		priv->last_hostname = hostname;
+
 		/* only cache it if it's a valid hostname */
 		if (nm_utils_is_specific_hostname (hostname))
-			priv->orig_hostname = hostname;
-		else
-			g_free (hostname);
+			priv->orig_hostname = g_strdup (hostname);
 	}
 
 	priv->firewall_manager = g_object_ref (nm_firewall_manager_get ());
@@ -2310,6 +2368,7 @@ dispose (GObject *object)
 
 	g_clear_pointer (&priv->orig_hostname, g_free);
 	g_clear_pointer (&priv->cur_hostname, g_free);
+	g_clear_pointer (&priv->last_hostname, g_free);
 
 	if (priv->settings) {
 		g_signal_handlers_disconnect_by_data (priv->settings, priv);