dns: fix tracking of best ip configbg/dns-fix-best

When a IP configuration has type "best", it is the configuration with
the best (lowest) metric default route for the specific address
family. Therefore, there can be only one best configuration for
address family.

When a new configuration is added as best, make sure it is the only
one for the address family.

This reverts commit 0abc14b3a0d9259b2a17f2fe3c56444752f49215.

Fixes: 0abc14b3a0d9 ('core: remove unused best_ip_config_[46] field in NMDnsManager')

https://lists.freedesktop.org/archives/networkmanager/2023-June/000123.html
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1331
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1683

1 files changed, 26 insertions, 0 deletions

diff --git a/src/core/dns/nm-dns-manager.c b/src/core/dns/nm-dns-manager.c
index 2eeb48f21a..535646930c 100644
--- a/src/core/dns/nm-dns-manager.c
+++ b/src/core/dns/nm-dns-manager.c
@@ -125,6 +125,9 @@ typedef struct {
 
     NMConfig *config;
 
+    NMDnsConfigIPData *best_ip_config_4;
+    NMDnsConfigIPData *best_ip_config_6;
+
     struct {
         guint64 ts;
         guint   num_restarts;
@@ -1978,6 +1981,7 @@ nm_dns_manager_set_ip_config(NMDnsManager         *self,
     NMDnsConfigIPData   *ip_data = NULL;
     int                  dns_priority;
     gboolean             any_removed = FALSE;
+    NMDnsConfigIPData  **p_best;
 
     g_return_val_if_fail(NM_IS_DNS_MANAGER(self), FALSE);
     g_return_val_if_fail(!l3cd || NM_IS_L3_CONFIG_DATA(l3cd), FALSE);
@@ -2045,6 +2049,12 @@ nm_dns_manager_set_ip_config(NMDnsManager         *self,
             }
 
             any_removed = TRUE;
+
+            if (priv->best_ip_config_4 == ip_data_iter)
+                priv->best_ip_config_4 = NULL;
+            if (priv->best_ip_config_6 == ip_data_iter)
+                priv->best_ip_config_6 = NULL;
+
             _dns_config_ip_data_free(ip_data_iter);
         }
     }
@@ -2095,6 +2105,19 @@ nm_dns_manager_set_ip_config(NMDnsManager         *self,
         changed                 = TRUE;
     }
 
+    p_best = NM_IS_IPv4(addr_family) ? &priv->best_ip_config_4 : &priv->best_ip_config_6;
+    if (ip_config_type == NM_DNS_IP_CONFIG_TYPE_BEST_DEVICE) {
+        /* Only one best-device per IP version is allowed */
+        if (*p_best != ip_data) {
+            if (*p_best)
+                (*p_best)->ip_config_type = NM_DNS_IP_CONFIG_TYPE_DEFAULT;
+            *p_best = ip_data;
+        }
+    } else {
+        if (*p_best == ip_data)
+            *p_best = NULL;
+    }
+
     if (changed)
         priv->ip_data_lst_need_sort = TRUE;
 
@@ -2819,6 +2842,9 @@ dispose(GObject *object)
 
     nm_clear_g_source_inst(&priv->update_pending_unblock);
 
+    priv->best_ip_config_4 = NULL;
+    priv->best_ip_config_6 = NULL;
+
     c_list_for_each_entry_safe (ip_data, ip_data_safe, &priv->ip_data_lst_head, ip_data_lst)
         _dns_config_ip_data_free(ip_data);