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, 177 insertions, 3 deletions

diff --git a/src/or/hs_client.c b/src/or/hs_client.c
index 514ecf99ba..3f951a21af 100644
--- a/src/or/hs_client.c
+++ b/src/or/hs_client.c
@@ -10,13 +10,48 @@
 #include "hs_circuit.h"
 #include "hs_ident.h"
 #include "connection_edge.h"
+#include "container.h"
 #include "rendclient.h"
 #include "hs_descriptor.h"
 #include "hs_cache.h"
+#include "hs_cell.h"
+#include "hs_ident.h"
 #include "config.h"
 #include "directory.h"
 #include "hs_client.h"
 #include "router.h"
+#include "circuitlist.h"
+#include "circuituse.h"
+#include "connection.h"
+#include "circpathbias.h"
+
+/* Get all connections that are waiting on a circuit and flag them back to
+ * waiting for a hidden service descriptor for the given service key
+ * service_identity_pk. */
+static void
+flag_all_conn_wait_desc(const ed25519_public_key_t *service_identity_pk)
+{
+  tor_assert(service_identity_pk);
+
+  smartlist_t *conns =
+    connection_list_by_type_state(CONN_TYPE_AP, AP_CONN_STATE_CIRCUIT_WAIT);
+
+  SMARTLIST_FOREACH_BEGIN(conns, connection_t *, conn) {
+    edge_connection_t *edge_conn;
+    if (BUG(!CONN_IS_EDGE(conn))) {
+      continue;
+    }
+    edge_conn = TO_EDGE_CONN(conn);
+    if (edge_conn->hs_ident &&
+        ed25519_pubkey_eq(&edge_conn->hs_ident->identity_pk,
+                          service_identity_pk)) {
+      connection_ap_mark_as_non_pending_circuit(TO_ENTRY_CONN(conn));
+      conn->state = AP_CONN_STATE_RENDDESC_WAIT;
+    }
+  } SMARTLIST_FOREACH_END(conn);
+
+  smartlist_free(conns);
+}
 
 /* A v3 HS circuit successfully connected to the hidden service. Update the
  * stream state at <b>hs_conn_ident</b> appropriately. */
@@ -140,11 +175,10 @@ fetch_v3_desc(const ed25519_public_key_t *onion_identity_pk)
   return directory_launch_v3_desc_fetch(onion_identity_pk, hsdir_rs);
 }
 
-#if 0
 /* Make sure that the given origin circuit circ is a valid correct
  * introduction circuit. This asserts on validation failure. */
 static void
-assert_intro_circ(const origin_circuit_t *circ)
+assert_intro_circ_ok(const origin_circuit_t *circ)
 {
   tor_assert(circ);
   tor_assert(circ->base_.purpose == CIRCUIT_PURPOSE_C_INTRODUCING);
@@ -152,7 +186,131 @@ assert_intro_circ(const origin_circuit_t *circ)
   tor_assert(hs_ident_intro_circ_is_valid(circ->hs_ident));
   assert_circ_anonymity_ok(circ, get_options());
 }
-#endif
+
+/* Find a descriptor intro point object that matches the given ident in the
+ * given descriptor desc. Return NULL if not found. */
+static const hs_desc_intro_point_t *
+find_desc_intro_point_by_ident(const hs_ident_circuit_t *ident,
+                               const hs_descriptor_t *desc)
+{
+  const hs_desc_intro_point_t *intro_point = NULL;
+
+  tor_assert(ident);
+  tor_assert(desc);
+
+  SMARTLIST_FOREACH_BEGIN(desc->encrypted_data.intro_points,
+                          const hs_desc_intro_point_t *, ip) {
+    if (ed25519_pubkey_eq(&ident->intro_auth_pk,
+                          &ip->auth_key_cert->signed_key)) {
+      intro_point = ip;
+      break;
+    }
+  } SMARTLIST_FOREACH_END(ip);
+
+  return intro_point;
+}
+
+/* Send an INTRODUCE1 cell along the intro circuit and populate the rend
+ * circuit identifier with the needed key material for the e2e encryption.
+ * Return 0 on success, -1 if there is a transient error such that an action
+ * has been taken to recover and -2 if there is a permanent error indicating
+ * that both circuits were closed. */
+static int
+send_introduce1(origin_circuit_t *intro_circ,
+                origin_circuit_t *rend_circ)
+{
+  int status;
+  char onion_address[HS_SERVICE_ADDR_LEN_BASE32 + 1];
+  const ed25519_public_key_t *service_identity_pk = NULL;
+  const hs_desc_intro_point_t *ip;
+
+  assert_intro_circ_ok(intro_circ);
+  tor_assert(rend_circ);
+
+  service_identity_pk = &intro_circ->hs_ident->identity_pk;
+  /* For logging purposes. There will be a time where the hs_ident will have a
+   * version number but for now there is none because it's all v3. */
+  hs_build_address(service_identity_pk, HS_VERSION_THREE, onion_address);
+
+  log_info(LD_REND, "Sending INTRODUCE1 cell to service %s on circuit %u",
+           safe_str_client(onion_address), TO_CIRCUIT(intro_circ)->n_circ_id);
+
+  /* 1) Get descriptor from our cache. */
+  const hs_descriptor_t *desc =
+    hs_cache_lookup_as_client(service_identity_pk);
+  if (desc == NULL || !hs_client_any_intro_points_usable(desc)) {
+    log_info(LD_REND, "Request to %s %s. Trying to fetch a new descriptor.",
+             safe_str_client(onion_address),
+             (desc) ? "didn't have usable intro points" :
+             "didn't have a descriptor");
+    hs_client_refetch_hsdesc(service_identity_pk);
+    /* We just triggered a refetch, make sure every connections are back
+     * waiting for that descriptor. */
+    flag_all_conn_wait_desc(service_identity_pk);
+    /* We just asked for a refetch so this is a transient error. */
+    goto tran_err;
+  }
+
+  /* We need to find which intro point in the descriptor we are connected to
+   * on intro_circ. */
+  ip = find_desc_intro_point_by_ident(intro_circ->hs_ident, desc);
+  if (BUG(ip == NULL)) {
+    /* If we can find a descriptor from this introduction circuit ident, we
+     * must have a valid intro point object. Permanent error. */
+    goto perm_err;
+  }
+
+  /* Send the INTRODUCE1 cell. */
+  if (hs_circ_send_introduce1(intro_circ, rend_circ, ip,
+                              desc->subcredential) < 0) {
+    /* Unable to send the cell, the intro circuit has been marked for close so
+     * this is a permanent error. */
+    tor_assert_nonfatal(TO_CIRCUIT(intro_circ)->marked_for_close);
+    goto perm_err;
+  }
+
+  /* Cell has been sent successfully. Copy the introduction point
+   * authentication and encryption key in the rendezvous circuit identifier so
+   * we can compute the ntor keys when we receive the RENDEZVOUS2 cell. */
+  memcpy(&rend_circ->hs_ident->intro_enc_pk, &ip->enc_key,
+         sizeof(rend_circ->hs_ident->intro_enc_pk));
+  ed25519_pubkey_copy(&rend_circ->hs_ident->intro_auth_pk,
+                      &intro_circ->hs_ident->intro_auth_pk);
+
+  /* Now, we wait for an ACK or NAK on this circuit. */
+  circuit_change_purpose(TO_CIRCUIT(intro_circ),
+                         CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT);
+  /* Set timestamp_dirty, because circuit_expire_building expects it to
+   * specify when a circuit entered the _C_INTRODUCE_ACK_WAIT state. */
+  TO_CIRCUIT(intro_circ)->timestamp_dirty = time(NULL);
+  pathbias_count_use_attempt(intro_circ);
+
+  /* Success. */
+  status = 0;
+  goto end;
+
+ perm_err:
+  /* Permanent error: it is possible that the intro circuit was closed prior
+   * because we weren't able to send the cell. Make sure we don't double close
+   * it which would result in a warning. */
+  if (!TO_CIRCUIT(intro_circ)->marked_for_close) {
+    circuit_mark_for_close(TO_CIRCUIT(intro_circ), END_CIRC_REASON_INTERNAL);
+  }
+  circuit_mark_for_close(TO_CIRCUIT(rend_circ), END_CIRC_REASON_INTERNAL);
+  status = -2;
+  goto end;
+
+ tran_err:
+  status = -1;
+
+ end:
+  memwipe(onion_address, 0, sizeof(onion_address));
+  return status;
+}
+
+/* ========== */
+/* Public API */
+/* ========== */
 
 /** A circuit just finished connecting to a hidden service that the stream
  *  <b>conn</b> has been waiting for. Let the HS subsystem know about this. */
@@ -256,3 +414,19 @@ hs_client_refetch_hsdesc(const ed25519_public_key_t *identity_pk)
   return fetch_v3_desc(identity_pk);
 }
 
+/* This is called when we are trying to attach an AP connection to these
+ * hidden service circuits from connection_ap_handshake_attach_circuit().
+ * Return 0 on success, -1 for a transient error that is actions were
+ * triggered to recover or -2 for a permenent error where both circuits will
+ * marked for close.
+ *
+ * The following supports every hidden service version. */
+int
+hs_client_send_introduce1(origin_circuit_t *intro_circ,
+                          origin_circuit_t *rend_circ)
+{
+  return (intro_circ->hs_ident) ? send_introduce1(intro_circ, rend_circ) :
+                                  rend_client_send_introduction(intro_circ,
+                                                                rend_circ);
+}
+