addr: New function relay_address_new_suggestion()

This behaves like router_new_address_suggestion() but differs in couple of
ways:

  1. It takes a tor_addr_t instead of an address string and supports both
     AF_INET and AF_INET6.
  2. It does _not_ use the last_guessed_ip local cache and instead only relies
     on the last resolved address cache in resolve_addr.c

It is not used at this commit. This function is made to process a suggested
address found in a NETINFO cell exactly like router_new_address_suggestion()
does with the address a directory suggests us.

Related to #40022

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

2 files changed, 57 insertions, 0 deletions

diff --git a/src/feature/relay/relay_find_addr.c b/src/feature/relay/relay_find_addr.c
index a51457ddbb..699eb7e380 100644
--- a/src/feature/relay/relay_find_addr.c
+++ b/src/feature/relay/relay_find_addr.c
@@ -15,6 +15,7 @@
 
 #include "feature/control/control_events.h"
 #include "feature/dircommon/dir_connection_st.h"
+#include "feature/nodelist/dirlist.h"
 #include "feature/relay/relay_find_addr.h"
 #include "feature/relay/router.h"
 #include "feature/relay/routermode.h"
@@ -37,6 +38,59 @@ router_guess_address_from_dir_headers(uint32_t *guess)
   return -1;
 }
 
+/** Consider the address suggestion suggested_addr as a possible one to use as
+ * our address.
+ *
+ * This is called when a valid NETINFO cell is recevied containing a candidate
+ * for our address.
+ *
+ * The suggested address is ignored if it does NOT come from a trusted source.
+ * At the moment, we only look a trusted directory authorities.
+ *
+ * The suggested address is ignored if it is internal or it is the same as the
+ * given peer_addr which is the address from the endpoint that sent the
+ * NETINFO cell.
+ *
+ * The suggested address is set in our suggested address cache if everything
+ * passes. */
+void
+relay_address_new_suggestion(const tor_addr_t *suggested_addr,
+                             const tor_addr_t *peer_addr)
+{
+  const or_options_t *options = get_options();
+
+  tor_assert(suggested_addr);
+  tor_assert(peer_addr);
+
+  /* This should never be called on a non Tor relay. */
+  if (BUG(!server_mode(options))) {
+    return;
+  }
+
+  /* Is the peer a trusted source? Ignore anything coming from non trusted
+   * source. In this case, we only look at trusted authorities. */
+  if (!router_addr_is_trusted_dir(peer_addr)) {
+    return;
+  }
+
+  /* Ignore a suggestion that is an internal address or the same as the one
+   * the peer address. */
+  if (tor_addr_is_internal(suggested_addr, 0)) {
+    /* Do not believe anyone who says our address is internal. */
+    return;
+  }
+  if (tor_addr_eq(suggested_addr, peer_addr)) {
+    /* Do not believe anyone who says our address is their address. */
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "A relay endpoint %s is telling us that their address is ours.",
+           fmt_addr(peer_addr));
+    return;
+  }
+
+  /* Save the suggestion in our cache. */
+  resolved_addr_set_suggested(suggested_addr);
+}
+
 /** A directory server <b>d_conn</b> told us our IP address is
  * <b>suggestion</b>.
  * If this address is different from the one we think we are now, and
diff --git a/src/feature/relay/relay_find_addr.h b/src/feature/relay/relay_find_addr.h
index ac51a977e6..d856e706ea 100644
--- a/src/feature/relay/relay_find_addr.h
+++ b/src/feature/relay/relay_find_addr.h
@@ -15,6 +15,9 @@ MOCK_DECL(int, router_pick_published_address,
 void router_new_address_suggestion(const char *suggestion,
                                    const dir_connection_t *d_conn);
 
+void relay_address_new_suggestion(const tor_addr_t *suggested_addr,
+                                  const tor_addr_t *peer_addr);
+
 #ifdef RELAY_FIND_ADDR_PRIVATE
 
 #endif /* RELAY_FIND_ADDR_PRIVATE */