core: fix crash when reloading global dns configuration

When reloading the configuration and there is a global DNS
configuration without domains, NM crashes in global_dns_equal()
because `old->domains` and `new->domains` are both NULL. Fix that.

  Thread 1 "NetworkManager" received signal SIGTRAP, Trace/breakpoint trap.
  0  g_logv (log_domain=0x7fe81a2110be "GLib", log_level=G_LOG_LEVEL_CRITICAL, format=<optimized out>, args=<optimized out>) at ../glib/gmessages.c:1433
  1  g_log (log_domain=<optimized out>, log_level=<optimized out>, format=<optimized out>) at ../glib/gmessages.c:1471
  2  g_hash_table_size (hash_table=<optimized out>) at ../glib/ghash.c:2183
  3  g_hash_table_size (hash_table=<optimized out>) at ../glib/ghash.c:2181
  4  global_dns_equal (new=0xecc540, old=0xe618e0) at ../src/core/nm-config-data.c:1466
  5  nm_config_data_diff (old_data=old_data@entry=0xe60020, new_data=new_data@entry=0xe606a0) at ../src/core/nm-config-data.c:1946
  6  _set_config_data (self=0xe45810, new_data=0xe606a0, reload_flags=NM_CONFIG_CHANGE_CAUSE_SIGHUP) at ../src/core/nm-config.c:2923
  7  nm_config_reload (self=0xe45810, reload_flags=NM_CONFIG_CHANGE_CAUSE_SIGHUP, emit_warnings=emit_warnings@entry=1) at ../src/core/nm-config.c:2875
  8  nm_main_config_reload (signal=<optimized out>) at ../src/core/main.c:141
  9  sighup_handler (user_data=<optimized out>) at ../src/core/main-utils.c:26
  10 g_main_dispatch (context=0xe619e0) at ../glib/gmain.c:3444
  11 g_main_context_dispatch (context=0xe619e0) at ../glib/gmain.c:4162
  12 g_main_context_iterate.constprop.0 (context=0xe619e0, block=1, dispatch=1, self=<optimized out>) at ../glib/gmain.c:4238
  13 g_main_loop_run (loop=0xe5e310) at ../glib/gmain.c:4438
  14 main (argc=<optimized out>, argv=<optimized out>) at ../src/core/main.c:515

Fixes: 1f0d1d78d2a2 ('dns-manager: always apply options from [global-dns]')

1 files changed, 13 insertions, 11 deletions

diff --git a/src/core/nm-config-data.c b/src/core/nm-config-data.c
index c6ab998f94..ff44bc46b3 100644
--- a/src/core/nm-config-data.c
+++ b/src/core/nm-config-data.c
@@ -1463,21 +1463,23 @@ global_dns_equal(NMGlobalDnsConfig *old, NMGlobalDnsConfig *new)
     if ((!old->domains || !new->domains) && old->domains != new->domains)
         return FALSE;
 
-    if (g_hash_table_size(old->domains) != g_hash_table_size(new->domains))
+    if (nm_g_hash_table_size(old->domains) != nm_g_hash_table_size(new->domains))
         return FALSE;
 
-    g_hash_table_iter_init(&iter, old->domains);
-    while (g_hash_table_iter_next(&iter, &key, &value_old)) {
-        value_new = g_hash_table_lookup(new->domains, key);
-        if (!value_new)
-            return FALSE;
+    if (old->domains) {
+        g_hash_table_iter_init(&iter, old->domains);
+        while (g_hash_table_iter_next(&iter, &key, &value_old)) {
+            value_new = g_hash_table_lookup(new->domains, key);
+            if (!value_new)
+                return FALSE;
 
-        domain_old = value_old;
-        domain_new = value_new;
+            domain_old = value_old;
+            domain_new = value_new;
 
-        if (!nm_strv_equal(domain_old->options, domain_new->options)
-            || !nm_strv_equal(domain_old->servers, domain_new->servers))
-            return FALSE;
+            if (!nm_strv_equal(domain_old->options, domain_new->options)
+                || !nm_strv_equal(domain_old->servers, domain_new->servers))
+                return FALSE;
+        }
     }
 
     return TRUE;