resolved: reference count the dns servers

We want to reference the servers from their active transactions, so make sure
they stay around as long as the transaction does.

4 files changed, 73 insertions, 31 deletions

diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
index 9a62a63258..92e48ae442 100644
--- a/src/resolve/resolved-dns-server.c
+++ b/src/resolve/resolved-dns-server.c
@@ -41,6 +41,7 @@ int dns_server_new(
         if (!s)
                 return -ENOMEM;
 
+        s->n_ref = 1;
         s->type = type;
         s->family = family;
         s->address = *in_addr;
@@ -74,33 +75,46 @@ int dns_server_new(
         return 0;
 }
 
-DnsServer* dns_server_free(DnsServer *s)  {
+DnsServer* dns_server_ref(DnsServer *s)  {
         if (!s)
                 return NULL;
 
-        if (s->link) {
-                if (s->type == DNS_SERVER_LINK)
-                        LIST_REMOVE(servers, s->link->dns_servers, s);
+        assert(s->n_ref > 0);
 
-                if (s->link->current_dns_server == s)
-                        link_set_dns_server(s->link, NULL);
-        }
+        s->n_ref ++;
 
-        if (s->manager) {
-                if (s->type == DNS_SERVER_SYSTEM)
-                        LIST_REMOVE(servers, s->manager->dns_servers, s);
-                else if (s->type == DNS_SERVER_FALLBACK)
-                        LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
+        return s;
+}
+
+static DnsServer* dns_server_free(DnsServer *s)  {
+        if (!s)
+                return NULL;
 
-                if (s->manager->current_dns_server == s)
-                        manager_set_dns_server(s->manager, NULL);
-        }
+        if (s->link && s->link->current_dns_server == s)
+                link_set_dns_server(s->link, NULL);
+
+        if (s->manager && s->manager->current_dns_server == s)
+                manager_set_dns_server(s->manager, NULL);
 
         free(s);
 
         return NULL;
 }
 
+DnsServer* dns_server_unref(DnsServer *s)  {
+        if (!s)
+                return NULL;
+
+        assert(s->n_ref > 0);
+
+        if (s->n_ref == 1)
+                dns_server_free(s);
+        else
+                s->n_ref --;
+
+        return NULL;
+}
+
 static unsigned long dns_server_hash_func(const void *p, const uint8_t hash_key[HASH_KEY_SIZE]) {
         const DnsServer *s = p;
         uint64_t u;
diff --git a/src/resolve/resolved-dns-server.h b/src/resolve/resolved-dns-server.h
index 70ff35b08f..03013beb82 100644
--- a/src/resolve/resolved-dns-server.h
+++ b/src/resolve/resolved-dns-server.h
@@ -37,6 +37,8 @@ typedef enum DnsServerType {
 struct DnsServer {
         Manager *manager;
 
+        unsigned n_ref;
+
         DnsServerType type;
 
         Link *link;
@@ -57,6 +59,7 @@ int dns_server_new(
                 int family,
                 const union in_addr_union *address);
 
-DnsServer* dns_server_free(DnsServer *s);
+DnsServer* dns_server_ref(DnsServer *s);
+DnsServer* dns_server_unref(DnsServer *s);
 
 extern const struct hash_ops dns_server_hash_ops;
diff --git a/src/resolve/resolved-link.c b/src/resolve/resolved-link.c
index ff8dc3a5bc..d66b3a88fc 100644
--- a/src/resolve/resolved-link.c
+++ b/src/resolve/resolved-link.c
@@ -58,7 +58,6 @@ int link_new(Manager *m, Link **ret, int ifindex) {
 }
 
 Link *link_free(Link *l) {
-
         if (!l)
                 return NULL;
 
@@ -68,8 +67,12 @@ Link *link_free(Link *l) {
         if (l->manager)
                 hashmap_remove(l->manager->links, INT_TO_PTR(l->ifindex));
 
-        while (l->dns_servers)
-                dns_server_free(l->dns_servers);
+        while (l->dns_servers) {
+                DnsServer *s = l->dns_servers;
+
+                LIST_REMOVE(servers, l->dns_servers, s);
+                dns_server_unref(s);
+        }
 
         dns_scope_free(l->unicast_scope);
         dns_scope_free(l->llmnr_ipv4_scope);
@@ -182,14 +185,20 @@ static int link_update_dns_servers(Link *l) {
         }
 
         LIST_FOREACH_SAFE(servers, s, nx, l->dns_servers)
-                if (s->marked)
-                        dns_server_free(s);
+                if (s->marked) {
+                        LIST_REMOVE(servers, l->dns_servers, s);
+                        dns_server_unref(s);
+                }
 
         return 0;
 
 clear:
-        while (l->dns_servers)
-                dns_server_free(l->dns_servers);
+        while (l->dns_servers) {
+                s = l->dns_servers;
+
+                LIST_REMOVE(servers, l->dns_servers, s);
+                dns_server_unref(s);
+        }
 
         return r;
 }
diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index 6785a2e3c7..e050092a12 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -603,8 +603,10 @@ int manager_read_resolv_conf(Manager *m) {
         }
 
         LIST_FOREACH_SAFE(servers, s, nx, m->dns_servers)
-                if (s->marked)
-                        dns_server_free(s);
+                if (s->marked) {
+                        LIST_REMOVE(servers, m->dns_servers, s);
+                        dns_server_unref(s);
+                }
 
         /* Whenever /etc/resolv.conf changes, start using the first
          * DNS server of it. This is useful to deal with broken
@@ -619,8 +621,12 @@ int manager_read_resolv_conf(Manager *m) {
         return 0;
 
 clear:
-        while (m->dns_servers)
-                dns_server_free(m->dns_servers);
+        while (m->dns_servers) {
+                s = m->dns_servers;
+
+                LIST_REMOVE(servers, m->dns_servers, s);
+                dns_server_unref(s);
+        }
 
         return r;
 }
@@ -1381,15 +1387,25 @@ void manager_verify_all(Manager *m) {
 }
 
 void manager_flush_dns_servers(Manager *m, DnsServerType t) {
+        DnsServer *s;
+
         assert(m);
 
         if (t == DNS_SERVER_SYSTEM)
-                while (m->dns_servers)
-                        dns_server_free(m->dns_servers);
+                while (m->dns_servers) {
+                        s = m->dns_servers;
+
+                        LIST_REMOVE(servers, m->dns_servers, s);
+                        dns_server_unref(s);
+                }
 
         if (t == DNS_SERVER_FALLBACK)
-                while (m->fallback_dns_servers)
-                        dns_server_free(m->fallback_dns_servers);
+                while (m->fallback_dns_servers) {
+                        s = m->fallback_dns_servers;
+
+                        LIST_REMOVE(servers, m->fallback_dns_servers, s);
+                        dns_server_unref(s);
+                }
 }
 
 static const char* const support_table[_SUPPORT_MAX] = {