prop224: Build INTRODUCE1 cell and send logic

Add a function in hs_cell.{c|h} for a client to build an INTRODUCE1 cell using
an object that contains all the needed keys to do so.

Add an entry point in hs_client.c that allows a tor client to send an
INTRODUCE1 cell on a given introduction circuit.

It includes the building of the cell, sending it and the setup of the
rendezvous circuit with the circuit identifier.

The entry point function is still unused at this commit.

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

1 files changed, 147 insertions, 0 deletions

diff --git a/src/or/hs_circuit.c b/src/or/hs_circuit.c
index 7704fd0bad..95100e9b3a 100644
--- a/src/or/hs_circuit.c
+++ b/src/or/hs_circuit.c
@@ -530,6 +530,83 @@ retry_service_rendezvous_point(const origin_circuit_t *circ)
   return;
 }
 
+/* Using an extend info object ei, set all possible link specifiers in lspecs.
+ * IPv4, legacy ID and ed25519 ID are mandatory thus MUST be present in ei. */
+static void
+get_lspecs_from_extend_info(const extend_info_t *ei, smartlist_t *lspecs)
+{
+  link_specifier_t *ls;
+
+  tor_assert(ei);
+  tor_assert(lspecs);
+
+  /* IPv4 is mandatory. */
+  ls = link_specifier_new();
+  link_specifier_set_ls_type(ls, LS_IPV4);
+  link_specifier_set_un_ipv4_addr(ls, tor_addr_to_ipv4h(&ei->addr));
+  link_specifier_set_un_ipv4_port(ls, ei->port);
+  /* Four bytes IPv4 and two bytes port. */
+  link_specifier_set_ls_len(ls, sizeof(ei->addr.addr.in_addr) +
+                            sizeof(ei->port));
+  smartlist_add(lspecs, ls);
+
+  /* Legacy ID is mandatory. */
+  ls = link_specifier_new();
+  link_specifier_set_ls_type(ls, LS_LEGACY_ID);
+  memcpy(link_specifier_getarray_un_legacy_id(ls), ei->identity_digest,
+         link_specifier_getlen_un_legacy_id(ls));
+  link_specifier_set_ls_len(ls, link_specifier_getlen_un_legacy_id(ls));
+  smartlist_add(lspecs, ls);
+
+  /* ed25519 ID is mandatory. */
+  ls = link_specifier_new();
+  link_specifier_set_ls_type(ls, LS_ED25519_ID);
+  memcpy(link_specifier_getarray_un_ed25519_id(ls), &ei->ed_identity,
+         link_specifier_getlen_un_ed25519_id(ls));
+  link_specifier_set_ls_len(ls, link_specifier_getlen_un_ed25519_id(ls));
+  smartlist_add(lspecs, ls);
+
+  /* XXX: IPv6 is not clearly a thing in extend_info_t? */
+}
+
+/* Using the given descriptor intro point ip, the extend information of the
+ * rendezvous point rp_ei and the service's subcredential, populate the
+ * already allocated intro1_data object with the needed key material and link
+ * specifiers.
+ *
+ * This can't fail but the ip MUST be a valid object containing the needed
+ * keys and authentication method. */
+static void
+setup_introduce1_data(const hs_desc_intro_point_t *ip,
+                      const extend_info_t *rp_ei,
+                      const uint8_t *subcredential,
+                      hs_cell_introduce1_data_t *intro1_data)
+{
+  smartlist_t *rp_lspecs;
+
+  tor_assert(ip);
+  tor_assert(rp_ei);
+  tor_assert(subcredential);
+  tor_assert(intro1_data);
+
+  /* Build the link specifiers from the extend information of the rendezvous
+   * circuit that we've picked previously. */
+  rp_lspecs = smartlist_new();
+  get_lspecs_from_extend_info(rp_ei, rp_lspecs);
+
+  /* Populate the introduce1 data object. */
+  memset(intro1_data, 0, sizeof(hs_cell_introduce1_data_t));
+  if (ip->legacy.key != NULL) {
+    intro1_data->is_legacy = 1;
+    intro1_data->legacy_key = ip->legacy.key;
+  }
+  intro1_data->auth_pk = &ip->auth_key_cert->signed_key;
+  intro1_data->enc_pk = &ip->enc_key;
+  intro1_data->subcredential = subcredential;
+  intro1_data->onion_pk = &rp_ei->curve25519_onion_key;
+  intro1_data->link_specifiers = rp_lspecs;
+}
+
 /* ========== */
 /* Public API */
 /* ========== */
@@ -937,3 +1014,73 @@ hs_circuit_setup_e2e_rend_circ_legacy_client(origin_circuit_t *circ,
   return 0;
 }
 
+/* Given the introduction circuit intro_circ, the rendezvous circuit
+ * rend_circ, a descriptor intro point object ip and the service's
+ * subcredential, send an INTRODUCE1 cell on intro_circ.
+ *
+ * This will also setup the circuit identifier on rend_circ containing the key
+ * material for the handshake and e2e encryption. Return 0 on success else
+ * negative value. Because relay_send_command_from_edge() closes the circuit
+ * on error, it is possible that intro_circ is closed on error. */
+int
+hs_circ_send_introduce1(origin_circuit_t *intro_circ,
+                        origin_circuit_t *rend_circ,
+                        const hs_desc_intro_point_t *ip,
+                        const uint8_t *subcredential)
+{
+  int ret = -1;
+  ssize_t payload_len;
+  uint8_t payload[RELAY_PAYLOAD_SIZE] = {0};
+  hs_cell_introduce1_data_t intro1_data;
+
+  tor_assert(intro_circ);
+  tor_assert(rend_circ);
+  tor_assert(ip);
+  tor_assert(subcredential);
+
+  /* This takes various objects in order to populate the introduce1 data
+   * object which is used to build the content of the cell. */
+  setup_introduce1_data(ip, rend_circ->build_state->chosen_exit,
+                        subcredential, &intro1_data);
+
+  /* Final step before we encode a cell, we setup the circuit identifier which
+   * will generate both the rendezvous cookie and client keypair for this
+   * connection. Those are put in the ident. */
+  intro1_data.rendezvous_cookie = rend_circ->hs_ident->rendezvous_cookie;
+  intro1_data.client_kp = &rend_circ->hs_ident->rendezvous_client_kp;
+
+  memcpy(intro_circ->hs_ident->rendezvous_cookie,
+         rend_circ->hs_ident->rendezvous_cookie,
+         sizeof(intro_circ->hs_ident->rendezvous_cookie));
+
+  /* From the introduce1 data object, this will encode the INTRODUCE1 cell
+   * into payload which is then ready to be sent as is. */
+  payload_len = hs_cell_build_introduce1(&intro1_data, payload);
+  if (BUG(payload_len < 0)) {
+    goto done;
+  }
+
+  if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(intro_circ),
+                                   RELAY_COMMAND_INTRODUCE1,
+                                   (const char *) payload, payload_len,
+                                   intro_circ->cpath->prev) < 0) {
+    /* On error, circuit is closed. */
+    log_warn(LD_REND, "Unable to send INTRODUCE1 cell on circuit %u.",
+             TO_CIRCUIT(intro_circ)->n_circ_id);
+    goto done;
+  }
+
+  /* Success. */
+  ret = 0;
+  goto done;
+
+ done:
+  /* Object in this list have been moved to the cell object when building it
+   * so they've been freed earlier. We do that in order to avoid duplicating
+   * them leading to more memory and CPU time being used for nothing. */
+  smartlist_free(intro1_data.link_specifiers);
+  memwipe(&intro1_data, 0, sizeof(intro1_data));
+  memwipe(payload, 0, sizeof(payload));
+  return ret;
+}
+