relay: Use testing circuit instead of dummy descriptor fetch

Tor now can learn its address from a NETINFO cell coming from an authority.
Thus, instead from launching a dummy descriptor fetch to learn the address
from the directory response (unauthenticated), we simply now launch a one-hop
testing circuit.

Related to #40071Signed-off-by: David Goulet <dgoulet@torproject.org>

src/core/or/circuitlist.h

@@ -114,7 +114,9 @@
 #define CIRCUIT_PURPOSE_S_HSDIR_POST 20
 #define CIRCUIT_PURPOSE_S_HS_MAX_ 20
 
-/** A testing circuit; not meant to be used for actual traffic. */
+/** A testing circuit; not meant to be used for actual traffic. It is used for
+ * bandwidth measurement, reachability test and address discovery from an
+ * authority using the NETINFO cell. */
 #define CIRCUIT_PURPOSE_TESTING 21
 /** A controller made this circuit and Tor should not use it. */
 #define CIRCUIT_PURPOSE_CONTROLLER 22

src/feature/nodelist/routerlist.c

@@ -65,6 +65,9 @@
 #include "app/config/config.h"
 #include "core/mainloop/connection.h"
 #include "core/mainloop/mainloop.h"
+#include "core/or/circuitlist.h"
+#include "core/or/circuituse.h"
+#include "core/or/extendinfo.h"
 #include "core/or/policies.h"
 #include "feature/client/bridges.h"
 #include "feature/control/control_events.h"
@@ -137,7 +140,7 @@ static int signed_desc_digest_is_recognized(signed_descriptor_t *desc);
 static const char *signed_descriptor_get_body_impl(
                                               const signed_descriptor_t *desc,
                                               int with_annotations);
-static void launch_dummy_descriptor_download_as_needed(time_t now,
+static void launch_dummy_circuit_as_needed(time_t now,
                                    const or_options_t *options);
 
 /****************************************************************************/
@@ -2306,7 +2309,7 @@ update_all_descriptor_downloads(time_t now)
     return;
   update_router_descriptor_downloads(now);
   update_microdesc_downloads(now);
-  launch_dummy_descriptor_download_as_needed(now, get_options());
+  launch_dummy_circuit_as_needed(now, get_options());
 }
 
 /** Clear all our timeouts for fetching v3 directory stuff, and then
@@ -2760,23 +2763,20 @@ update_consensus_router_descriptor_downloads(time_t now, int is_vote,
   smartlist_free(no_longer_old);
 }
 
-/** How often should we launch a server/authority request to be sure of getting
+/** How often should we launch a circuit to an authority to be sure of getting
  * a guess for our IP? */
-/*XXXX+ this info should come from netinfo cells or something, or we should
- * do this only when we aren't seeing incoming data. see bug 652. */
 #define DUMMY_DOWNLOAD_INTERVAL (20*60)
 
 /** As needed, launch a dummy router descriptor fetch to see if our
  * address has changed. */
 static void
-launch_dummy_descriptor_download_as_needed(time_t now,
-                                           const or_options_t *options)
+launch_dummy_circuit_as_needed(time_t now, const or_options_t *options)
 {
-  static time_t last_dummy_download = 0;
+  static time_t last_dummy_circuit = 0;
   bool have_addr;
   tor_addr_t addr_out;
 
-  /* This dummy fetch only matter for relays. */
+  /* This dummy circuit only matter for relays. */
   if (!server_mode(options)) {
     return;
   }
@@ -2784,27 +2784,44 @@ launch_dummy_descriptor_download_as_needed(time_t now,
   /* 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 fetch to learn our address as a suggestion from an authority. */
+   * 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);
 
-  /* XXXX+ we could be smarter here; see notes on bug 652. */
-  /* If we're a server that doesn't have an address, we rely on directory
-   * fetches to learn when our address changes.  So if we haven't tried to get
-   * any routerdescs in a long time, try a dummy fetch now. */
-  if (!have_addr &&
-      last_descriptor_download_attempted + DUMMY_DOWNLOAD_INTERVAL < now &&
-      last_dummy_download + DUMMY_DOWNLOAD_INTERVAL < now) {
-    last_dummy_download = now;
-    /* XX/teor - do we want an authority here, because they are less likely
-     * to give us the wrong address? (See #17782)
-     * I'm leaving the previous behaviour intact, because I don't like
-     * the idea of some relays contacting an authority every 20 minutes. */
-    directory_get_from_dirserver(DIR_PURPOSE_FETCH_SERVERDESC,
-                                 ROUTER_PURPOSE_GENERAL, "authority.z",
-                                 PDS_RETRY_IF_NO_SERVERS,
-                                 DL_WANT_ANY_DIRSERVER);
+  /* 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);
   }
 }