circuitbuild: Allow relays to send IPv6 extend cells

Allow relays and bridges to send IPv4 or IPv6 extend cells.
But keep restricting clients to IPv4 extend cells, because sending IPv6
extend cells would be an obvious version distinguisher.

Part of 33222.

1 files changed, 25 insertions, 6 deletions

diff --git a/src/core/or/circuitbuild.c b/src/core/or/circuitbuild.c
index 75581abd33..c4d544a64c 100644
--- a/src/core/or/circuitbuild.c
+++ b/src/core/or/circuitbuild.c
@@ -1075,14 +1075,25 @@ circuit_send_intermediate_onion_skin(origin_circuit_t *circ,
                                      crypt_path_t *hop)
 {
   int len;
+  int family = tor_addr_family(&hop->extend_info->addr);
   extend_cell_t ec;
   memset(&ec, 0, sizeof(ec));
 
   log_debug(LD_CIRC,"starting to send subsequent skin.");
 
-  if (tor_addr_family(&hop->extend_info->addr) != AF_INET) {
-    log_warn(LD_BUG, "Trying to extend to a non-IPv4 address.");
-    return - END_CIRC_REASON_INTERNAL;
+  /* Relays and bridges can send IPv6 extends. But for clients, it's an
+   * obvious version distinguisher. */
+  if (server_mode(get_options())) {
+    if (family != AF_INET && family != AF_INET6) {
+      log_warn(LD_BUG, "Server trying to extend to an invalid address "
+               "family.");
+      return - END_CIRC_REASON_INTERNAL;
+    }
+  } else {
+    if (family != AF_INET) {
+      log_warn(LD_BUG, "Client trying to extend to a non-IPv4 address.");
+      return - END_CIRC_REASON_INTERNAL;
+    }
   }
 
   circuit_pick_extend_handshake(&ec.cell_type,
@@ -1090,9 +1101,17 @@ circuit_send_intermediate_onion_skin(origin_circuit_t *circ,
                                 &ec.create_cell.handshake_type,
                                 hop->extend_info);
 
-  tor_addr_copy(&ec.orport_ipv4.addr, &hop->extend_info->addr);
-  ec.orport_ipv4.port = hop->extend_info->port;
-  tor_addr_make_unspec(&ec.orport_ipv6.addr);
+  /* At the moment, extend_info only has one ORPort address. We'll add a
+   * second address in #34069, to support dual-stack extend cells. */
+  if (family == AF_INET) {
+    tor_addr_copy(&ec.orport_ipv4.addr, &hop->extend_info->addr);
+    ec.orport_ipv4.port = hop->extend_info->port;
+    tor_addr_make_unspec(&ec.orport_ipv6.addr);
+  } else {
+    tor_addr_copy(&ec.orport_ipv6.addr, &hop->extend_info->addr);
+    ec.orport_ipv6.port = hop->extend_info->port;
+    tor_addr_make_unspec(&ec.orport_ipv4.addr);
+  }
   memcpy(ec.node_id, hop->extend_info->identity_digest, DIGEST_LEN);
   /* Set the ED25519 identity too -- it will only get included
    * in the extend2 cell if we're configured to use it, though. */