resolved: when there's already somebody listening on the LLMNR ports, simple disable LLMNR and warn, but continue

This allows us to run resolved inside an nspawn container that shares
the network namespace with the host, if there's already an instance
running.

3 files changed, 77 insertions, 22 deletions

diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index 1b6dc8a4a3..5061d39c46 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -392,6 +392,63 @@ static int manager_watch_hostname(Manager *m) {
         return 0;
 }
 
+static void manager_llmnr_stop(Manager *m) {
+        assert(m);
+
+        m->llmnr_ipv4_udp_event_source = sd_event_source_unref(m->llmnr_ipv4_udp_event_source);
+        m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
+
+        m->llmnr_ipv6_udp_event_source = sd_event_source_unref(m->llmnr_ipv6_udp_event_source);
+        m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
+
+        m->llmnr_ipv4_tcp_event_source = sd_event_source_unref(m->llmnr_ipv4_tcp_event_source);
+        m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
+
+        m->llmnr_ipv6_tcp_event_source = sd_event_source_unref(m->llmnr_ipv6_tcp_event_source);
+        m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
+}
+
+static int manager_llmnr_start(Manager *m) {
+        int r;
+
+        assert(m);
+
+        if (m->llmnr_support == SUPPORT_NO)
+                return 0;
+
+        r = manager_llmnr_ipv4_udp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        r = manager_llmnr_ipv6_udp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        r = manager_llmnr_ipv4_tcp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        r = manager_llmnr_ipv6_tcp_fd(m);
+        if (r == -EADDRINUSE)
+                goto eaddrinuse;
+        if (r < 0)
+                return r;
+
+        return 0;
+
+eaddrinuse:
+        log_warning("There appears to be another LLMNR respondering running. Turning off LLMNR support.");
+        m->llmnr_support = SUPPORT_NO;
+        manager_llmnr_stop(m);
+        return 0;
+}
+
 int manager_new(Manager **ret) {
         _cleanup_(manager_freep) Manager *m = NULL;
         int r;
@@ -443,25 +500,24 @@ int manager_new(Manager **ret) {
         if (r < 0)
                 return r;
 
-        r = manager_llmnr_ipv4_udp_fd(m);
-        if (r < 0)
-                return r;
-        r = manager_llmnr_ipv6_udp_fd(m);
-        if (r < 0)
-                return r;
-        r = manager_llmnr_ipv4_tcp_fd(m);
-        if (r < 0)
-                return r;
-        r = manager_llmnr_ipv6_tcp_fd(m);
-        if (r < 0)
-                return r;
-
         *ret = m;
         m = NULL;
 
         return 0;
 }
 
+int manager_start(Manager *m) {
+        int r;
+
+        assert(m);
+
+        r = manager_llmnr_start(m);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
 Manager *manager_free(Manager *m) {
         Link *l;
 
@@ -492,15 +548,7 @@ Manager *manager_free(Manager *m) {
         safe_close(m->dns_ipv4_fd);
         safe_close(m->dns_ipv6_fd);
 
-        sd_event_source_unref(m->llmnr_ipv4_udp_event_source);
-        sd_event_source_unref(m->llmnr_ipv6_udp_event_source);
-        safe_close(m->llmnr_ipv4_udp_fd);
-        safe_close(m->llmnr_ipv6_udp_fd);
-
-        sd_event_source_unref(m->llmnr_ipv4_tcp_event_source);
-        sd_event_source_unref(m->llmnr_ipv6_tcp_event_source);
-        safe_close(m->llmnr_ipv4_tcp_fd);
-        safe_close(m->llmnr_ipv6_tcp_fd);
+        manager_llmnr_stop(m);
 
         sd_event_source_unref(m->bus_retry_event_source);
         sd_bus_unref(m->bus);
diff --git a/src/resolve/resolved-manager.h b/src/resolve/resolved-manager.h
index 31d670da44..1fd4be41a4 100644
--- a/src/resolve/resolved-manager.h
+++ b/src/resolve/resolved-manager.h
@@ -114,6 +114,7 @@ struct Manager {
 int manager_new(Manager **ret);
 Manager* manager_free(Manager *m);
 
+int manager_start(Manager *m);
 int manager_read_resolv_conf(Manager *m);
 int manager_write_resolv_conf(Manager *m);
 
diff --git a/src/resolve/resolved.c b/src/resolve/resolved.c
index 900a36d8f0..892bb51386 100644
--- a/src/resolve/resolved.c
+++ b/src/resolve/resolved.c
@@ -75,6 +75,12 @@ int main(int argc, char *argv[]) {
         if (r < 0)
                 log_warning("Failed to parse configuration file: %s", strerror(-r));
 
+        r = manager_start(m);
+        if (r < 0) {
+                log_error("Failed to start manager: %s", strerror(-r));
+                goto finish;
+        }
+
         /* Write finish default resolv.conf to avoid a dangling
          * symlink */
         r = manager_write_resolv_conf(m);