relay: Launch dummy circuit only when descriptor build fails

First, this commit moves the launch_dummy_circuit_as_needed() function into
relay_find_addr.c and renames it to relay_addr_learn_from_dirauth(). This is
an attempt to centralize anything relate with address discovery in the right
module.

Second, when building a descriptor and we fail to discover our address,
immediately launch a dummy circuit to an authority in an attempt to learn our
descriptor.

It is still only done every 20 minutes even though the descriptor build is
done every minute. We ought to avoid load on the authority and if we can't
learn in the first place our address from them, chances are more things are
wrong.

Related to #40071

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/src/feature/relay/relay_find_addr.c b/src/feature/relay/relay_find_addr.c
index 43b958d563..9c2c8b281c 100644
--- a/src/feature/relay/relay_find_addr.c
+++ b/src/feature/relay/relay_find_addr.c
@@ -12,10 +12,16 @@
 #include "app/config/resolve_addr.h"
 
 #include "core/mainloop/mainloop.h"
+#include "core/or/circuitlist.h"
+#include "core/or/circuituse.h"
+#include "core/or/extendinfo.h"
 
 #include "feature/control/control_events.h"
 #include "feature/dircommon/dir_connection_st.h"
 #include "feature/nodelist/dirlist.h"
+#include "feature/nodelist/node_select.h"
+#include "feature/nodelist/nodelist.h"
+#include "feature/nodelist/routerstatus_st.h"
 #include "feature/relay/relay_find_addr.h"
 #include "feature/relay/router.h"
 #include "feature/relay/routermode.h"
@@ -151,3 +157,65 @@ relay_has_address_set(int family)
   return relay_find_addr_to_publish(get_options(), family,
                                     RELAY_FIND_ADDR_CACHE_ONLY, &addr);
 }
+
+/** How often should we launch a circuit to an authority to be sure of getting
+ * a guess for our IP? */
+#define DUMMY_DOWNLOAD_INTERVAL (20*60)
+
+void
+relay_addr_learn_from_dirauth(void)
+{
+  static time_t last_dummy_circuit = 0;
+  const or_options_t *options = get_options();
+  time_t now = time(NULL);
+  bool have_addr;
+  tor_addr_t addr_out;
+
+  /* This dummy circuit only matter for relays. */
+  if (BUG(!server_mode(options))) {
+    return;
+  }
+
+  /* Lookup the address cache to learn if we have a good usable address. We
+   * still force relays to have an IPv4 so that alone is enough to learn if we
+   * need a lookup. In case we don't have one, we might want to attempt a
+   * dummy circuit to learn our address as a suggestion from an authority. */
+  have_addr = relay_find_addr_to_publish(options, AF_INET,
+                                         RELAY_FIND_ADDR_CACHE_ONLY,
+                                         &addr_out);
+
+  /* If we're a relay or bridge for which we were unable to discover our
+   * public address, we rely on learning our address from a directory
+   * authority from the NETINFO cell. */
+  if (!have_addr && last_dummy_circuit + DUMMY_DOWNLOAD_INTERVAL < now) {
+    last_dummy_circuit = now;
+
+    const routerstatus_t *rs = router_pick_trusteddirserver(V3_DIRINFO, 0);
+    if (BUG(!rs)) {
+      /* We should really always have trusted directories configured at this
+       * stage. They are loaded early either from default list or the one
+       * given in the configuration file. */
+      return;
+    }
+    const node_t *node = node_get_by_id(rs->identity_digest);
+    if (BUG(!node)) {
+      /* If there is a routerstatus_t, there is a node_t thus this should
+       * never fail. */
+      return;
+    }
+    extend_info_t *ei = extend_info_from_node(node, 1);
+    if (BUG(!ei)) {
+      return;
+    }
+
+    log_debug(LD_GENERAL, "Attempting dummy testing circuit to an authority "
+                          "in order to learn our address.");
+
+    /* Launch a one-hop testing circuit to a trusted authority so we can learn
+     * our address through the NETINFO cell. */
+    circuit_launch_by_extend_info(CIRCUIT_PURPOSE_TESTING, ei,
+                                  CIRCLAUNCH_IS_INTERNAL |
+                                  CIRCLAUNCH_ONEHOP_TUNNEL);
+    extend_info_free(ei);
+  }
+}