resolved: rework dns server lifecycle logic

Previously, there was a chance of memory corruption, because when
switching to the next DNS server we didn't care whether they linked list
of DNS servers was still valid.

Clean up lifecycle of the dns server logic:

- When a DnsServer object is still in the linked list of DnsServers for
  a link or the manager, indicate so with a "linked" boolean field, and
  never follow the linked list if that boolean is not set.

- When picking a DnsServer to use for a link ot manager, always
  explicitly take a reference.

This also rearranges some logic, to make the tracking of dns servers by
link and globally more alike.

1 files changed, 2 insertions, 10 deletions

diff --git a/src/resolve/resolved-resolv-conf.c b/src/resolve/resolved-resolv-conf.c
index 5a6e3812df..98c1720f0f 100644
--- a/src/resolve/resolved-resolv-conf.c
+++ b/src/resolve/resolved-resolv-conf.c
@@ -36,7 +36,6 @@ int manager_read_resolv_conf(Manager *m) {
         _cleanup_fclose_ FILE *f = NULL;
         struct stat st, own;
         char line[LINE_MAX];
-        DnsServer *s;
         usec_t t;
         int r;
 
@@ -53,7 +52,7 @@ int manager_read_resolv_conf(Manager *m) {
                 if (errno == ENOENT)
                         r = 0;
                 else
-                        r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
+                        r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
                 goto clear;
         }
 
@@ -89,7 +88,6 @@ int manager_read_resolv_conf(Manager *m) {
         manager_mark_dns_servers(m, DNS_SERVER_SYSTEM);
 
         FOREACH_LINE(line, f, r = -errno; goto clear) {
-                _cleanup_strv_free_ char **d = NULL;
                 const char *a;
                 char *l;
 
@@ -124,13 +122,7 @@ int manager_read_resolv_conf(Manager *m) {
         return 0;
 
 clear:
-        while (m->dns_servers) {
-                s = m->dns_servers;
-
-                LIST_REMOVE(servers, m->dns_servers, s);
-                dns_server_unref(s);
-        }
-
+        manager_flush_dns_servers(m, DNS_SERVER_SYSTEM);
         return r;
 }