resolved: do not disable mdns/llmnr globally if it's enabled on any link (#36158)

Fixes a regression caused by 2976730a4d.
Fixes #36078.
Fixes #36126.

Replaces #36153.
Replaces #36156.

src/resolve/resolved-link-bus.c

@@ -14,6 +14,8 @@
 #include "resolve-util.h"
 #include "resolved-bus.h"
 #include "resolved-link-bus.h"
+#include "resolved-llmnr.h"
+#include "resolved-mdns.h"
 #include "resolved-resolv-conf.h"
 #include "socket-netlink.h"
 #include "stdio-util.h"
@@ -517,6 +519,8 @@ int bus_link_method_set_llmnr(sd_bus_message *message, void *userdata, sd_bus_er
 
                 (void) link_save_user(l);
 
+                manager_llmnr_maybe_stop(l->manager);
+
                 log_link_info(l, "Bus client set LLMNR setting: %s", resolve_support_to_string(mode));
         }
 
@@ -567,6 +571,8 @@ int bus_link_method_set_mdns(sd_bus_message *message, void *userdata, sd_bus_err
 
                 (void) link_save_user(l);
 
+                manager_mdns_maybe_stop(l->manager);
+
                 log_link_info(l, "Bus client set MulticastDNS setting: %s", resolve_support_to_string(mode));
         }
 
@@ -769,6 +775,9 @@ int bus_link_method_revert(sd_bus_message *message, void *userdata, sd_bus_error
         (void) manager_write_resolv_conf(l->manager);
         (void) manager_send_changed(l->manager, "DNS");
 
+        manager_llmnr_maybe_stop(l->manager);
+        manager_mdns_maybe_stop(l->manager);
+
         return sd_bus_reply_method_return(message, NULL);
 }
 

src/resolve/resolved-link.c

@@ -651,16 +651,13 @@ int link_update(Link *l) {
                 r = manager_llmnr_start(l->manager);
                 if (r < 0)
                         return r;
-        } else
-                manager_llmnr_stop(l->manager);
-
+        }
 
         if (link_get_mdns_support(l) != RESOLVE_SUPPORT_NO) {
                 r = manager_mdns_start(l->manager);
                 if (r < 0)
                         return r;
-        } else
-                manager_mdns_stop(l->manager);
+        }
 
         link_allocate_scopes(l);
         link_add_rrs(l, false);

src/resolve/resolved-llmnr.c

@@ -25,6 +25,19 @@ void manager_llmnr_stop(Manager *m) {
         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 }
 
+void manager_llmnr_maybe_stop(Manager *m) {
+        assert(m);
+
+        /* This stops LLMNR only when no interface enables LLMNR. */
+
+        Link *l;
+        HASHMAP_FOREACH(l, m->links)
+                if (link_get_llmnr_support(l) != RESOLVE_SUPPORT_NO)
+                        return;
+
+        manager_llmnr_stop(m);
+}
+
 int manager_llmnr_start(Manager *m) {
         int r;
 

src/resolve/resolved-llmnr.h

@@ -11,4 +11,5 @@ int manager_llmnr_ipv4_tcp_fd(Manager *m);
 int manager_llmnr_ipv6_tcp_fd(Manager *m);
 
 void manager_llmnr_stop(Manager *m);
+void manager_llmnr_maybe_stop(Manager *m);
 int manager_llmnr_start(Manager *m);

src/resolve/resolved-manager.c

@@ -105,6 +105,9 @@ static int manager_process_link(sd_netlink *rtnl, sd_netlink_message *mm, void *
                 break;
         }
 
+        /* Now check all the links, and if mDNS/llmr are disabled everywhere, stop them globally too. */
+        manager_llmnr_maybe_stop(m);
+        manager_mdns_maybe_stop(m);
         return 0;
 
 fail:
@@ -287,6 +290,9 @@ static int on_network_event(sd_event_source *s, int fd, uint32_t revents, void *
         (void) manager_write_resolv_conf(m);
         (void) manager_send_changed(m, "DNS");
 
+        /* Now check all the links, and if mDNS/llmr are disabled everywhere, stop them globally too. */
+        manager_llmnr_maybe_stop(m);
+        manager_mdns_maybe_stop(m);
         return 0;
 }
 

src/resolve/resolved-mdns.c

@@ -22,6 +22,19 @@ void manager_mdns_stop(Manager *m) {
         m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
 }
 
+void manager_mdns_maybe_stop(Manager *m) {
+        assert(m);
+
+        /* This stops mDNS only when no interface enables mDNS. */
+
+        Link *l;
+        HASHMAP_FOREACH(l, m->links)
+                if (link_get_mdns_support(l) != RESOLVE_SUPPORT_NO)
+                        return;
+
+        manager_mdns_stop(m);
+}
+
 int manager_mdns_start(Manager *m) {
         int r;
 

src/resolve/resolved-mdns.h

@@ -10,4 +10,5 @@ int manager_mdns_ipv4_fd(Manager *m);
 int manager_mdns_ipv6_fd(Manager *m);
 
 void manager_mdns_stop(Manager *m);
+void manager_mdns_maybe_stop(Manager *m);
 int manager_mdns_start(Manager *m);