resolve: stop timer event source and detach from browser when a dnssd service is removed

Otherwise, if the timer event source is enabled, a new query may be
invoked by the already removed service.

This also renames dns_remove_service() to dnssd_discovered_service_detach(),
and drops unused DnssdDiscoveredService.query.

(cherry picked from commit 02f65ebead)

src/resolve/resolved-dns-browse-services.c

@@ -108,6 +108,8 @@ static int mdns_maintenance_query(sd_event_source *s, uint64_t usec, void *userd
         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
         int r;
 
+        assert(service->service_browser);
+
         /* Check if the TTL state has reached the maximum value, then revisit
          * cache */
         if (service->rr_ttl_state++ == DNS_RECORD_TTL_STATE_100_PERCENT)
@@ -171,12 +173,10 @@ int dns_add_new_service(DnsServiceBrowser *sb, DnsResourceRecord *rr, int owner_
 
         *s = (DnssdDiscoveredService) {
                 .n_ref = 1,
-                .service_browser = sb,
                 .rr = dns_resource_record_copy(rr),
                 .family = owner_family,
                 .ifindex = ifindex,
                 .until = until,
-                .query = NULL,
                 .rr_ttl_state = DNS_RECORD_TTL_STATE_80_PERCENT,
         };
         if (!s->rr)
@@ -221,34 +221,39 @@ int dns_add_new_service(DnsServiceBrowser *sb, DnsResourceRecord *rr, int owner_
                                 "Failed to schedule mDNS maintenance query for DNS service: %m");
 
         LIST_PREPEND(dns_services, sb->dns_services, s);
-
+        s->service_browser = sb;
         TAKE_PTR(s);
         return 0;
 }
 
-void dns_remove_service(DnsServiceBrowser *sb, DnssdDiscoveredService *service) {
-        assert(sb);
+static DnssdDiscoveredService* dnssd_discovered_service_detach_impl(DnssdDiscoveredService *service) {
         assert(service);
 
-        LIST_REMOVE(dns_services, sb->dns_services, service);
-        dnssd_discovered_service_unref(service);
-}
-
-DnssdDiscoveredService *dns_service_free(DnssdDiscoveredService *service) {
-        if (!service)
-                return NULL;
-
         service->schedule_event = sd_event_source_disable_unref(service->schedule_event);
 
-        if (service->query && DNS_TRANSACTION_IS_LIVE(service->query->state))
-                dns_query_complete(service->query, DNS_TRANSACTION_ABORTED);
+        if (!service->service_browser)
+                return NULL; /* already detached */
 
+        LIST_REMOVE(dns_services, service->service_browser->dns_services, service);
+        service->service_browser = NULL;
+        return service; /* indicate that the service is detached. */
+}
+
+static void dnssd_discovered_service_detach(DnssdDiscoveredService *service) {
+        dnssd_discovered_service_unref(dnssd_discovered_service_detach_impl(service));
+}
+
+static DnssdDiscoveredService* dnssd_discovered_service_free(DnssdDiscoveredService *service) {
+        if (!service)
+                return NULL;
+
+        dnssd_discovered_service_detach_impl(service);
         service->rr = dns_resource_record_unref(service->rr);
 
         return mfree(service);
 }
 
-DEFINE_TRIVIAL_REF_UNREF_FUNC(DnssdDiscoveredService, dnssd_discovered_service, dns_service_free);
+DEFINE_TRIVIAL_REF_UNREF_FUNC(DnssdDiscoveredService, dnssd_discovered_service, dnssd_discovered_service_free);
 
 int mdns_service_update(DnssdDiscoveredService *service, DnsResourceRecord *rr, usec_t t, usec_t until) {
         assert(service);
@@ -498,7 +503,7 @@ int mdns_manage_services_answer(DnsServiceBrowser *sb, DnsAnswer *answer, int ow
                 /* Capture ifindex before removing the service */
                 ifindex = service->ifindex;
 
-                dns_remove_service(sb, service);
+                dnssd_discovered_service_detach(service);
 
                 log_debug("Remove from the list %s, %s, %s, %s, %d",
                           strna(name),
@@ -904,7 +909,7 @@ static DnsServiceBrowser* dns_service_browser_detach_impl(DnsServiceBrowser *sb)
         assert(!sb->manager == !sb->link);
 
         while (sb->dns_services)
-                dns_remove_service(sb, sb->dns_services);
+                dnssd_discovered_service_detach(sb->dns_services);
 
         sb->schedule_event = sd_event_source_disable_unref(sb->schedule_event);
 

src/resolve/resolved-dns-browse-services.h

@@ -33,7 +33,6 @@ struct DnssdDiscoveredService {
         int ifindex;
         usec_t until;
         DnsRecordTTLState rr_ttl_state;
-        DnsQuery *query;
         LIST_FIELDS(DnssdDiscoveredService, dns_services);
 };
 
@@ -52,9 +51,6 @@ struct DnsServiceBrowser {
         LIST_HEAD(DnssdDiscoveredService, dns_services);
 };
 
-void dns_remove_service(DnsServiceBrowser *sb, DnssdDiscoveredService *service);
-DnssdDiscoveredService *dns_service_free(DnssdDiscoveredService *service);
-
 void dns_service_browser_detach(DnsServiceBrowser *sb);
 DECLARE_TRIVIAL_REF_UNREF_FUNC(DnsServiceBrowser, dns_service_browser);
 DECLARE_TRIVIAL_REF_UNREF_FUNC(DnssdDiscoveredService, dnssd_discovered_service);