circuituse.c

关于tor匿名通信的源代码

/* Copyright (c) 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2008, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/* $Id$ */
const char circuituse_c_id[] =
  "$Id$";

/**
 * \file circuituse.c
 * \brief Launch the right sort of circuits and attach streams to them.
 **/

#include "or.h"

/********* START VARIABLES **********/

extern circuit_t *global_circuitlist; /* from circuitlist.c */

/********* END VARIABLES ************/

static void circuit_expire_old_circuits(time_t now);
static void circuit_increment_failure_count(void);

/** Return 1 if <b>circ</b> could be returned by circuit_get_best().
 * Else return 0.
 */
static int
circuit_is_acceptable(circuit_t *circ, edge_connection_t *conn,
                      int must_be_open, uint8_t purpose,
                      int need_uptime, int need_internal,
                      time_t now)
{
  routerinfo_t *exitrouter;
  cpath_build_state_t *build_state;
  tor_assert(circ);
  tor_assert(conn);
  tor_assert(conn->socks_request);

  if (!CIRCUIT_IS_ORIGIN(circ))
    return 0; /* this circ doesn't start at us */
  if (must_be_open && (circ->state != CIRCUIT_STATE_OPEN || !circ->n_conn))
    return 0; /* ignore non-open circs */
  if (circ->marked_for_close)
    return 0;

  /* if this circ isn't our purpose, skip. */
  if (purpose == CIRCUIT_PURPOSE_C_REND_JOINED && !must_be_open) {
    if (circ->purpose != CIRCUIT_PURPOSE_C_ESTABLISH_REND &&
        circ->purpose != CIRCUIT_PURPOSE_C_REND_READY &&
        circ->purpose != CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED &&
        circ->purpose != CIRCUIT_PURPOSE_C_REND_JOINED)
      return 0;
  } else if (purpose == CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT &&
             !must_be_open) {
    if (circ->purpose != CIRCUIT_PURPOSE_C_INTRODUCING &&
        circ->purpose != CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT)
      return 0;
  } else {
    if (purpose != circ->purpose)
      return 0;
  }

  if (purpose == CIRCUIT_PURPOSE_C_GENERAL)
    if (circ->timestamp_dirty &&
       circ->timestamp_dirty+get_options()->MaxCircuitDirtiness <= now)
      return 0;

  /* decide if this circ is suitable for this conn */

  /* for rend circs, circ->cpath->prev is not the last router in the
   * circuit, it's the magical extra bob hop. so just check the nickname
   * of the one we meant to finish at.
   */
  build_state = TO_ORIGIN_CIRCUIT(circ)->build_state;
  exitrouter = build_state_get_exit_router(build_state);

  if (need_uptime && !build_state->need_uptime)
    return 0;
  if (need_internal != build_state->is_internal)
    return 0;

  if (purpose == CIRCUIT_PURPOSE_C_GENERAL) {
    if (!exitrouter && !build_state->onehop_tunnel) {
      log_debug(LD_CIRC,"Not considering circuit with unknown router.");
      return 0; /* this circuit is screwed and doesn't know it yet,
                 * or is a rendezvous circuit. */
    }
    if (build_state->onehop_tunnel) {
      if (!conn->want_onehop) {
        log_debug(LD_CIRC,"Skipping one-hop circuit.");
        return 0;
      }
      tor_assert(conn->chosen_exit_name);
      if (build_state->chosen_exit) {
        char digest[DIGEST_LEN];
        if (hexdigest_to_digest(conn->chosen_exit_name, digest) < 0 ||
            memcmp(digest, build_state->chosen_exit->identity_digest,
                   DIGEST_LEN))
          return 0; /* this is a circuit to somewhere else */
      }
    } else {
      if (conn->want_onehop) {
        /* don't use three-hop circuits -- that could hurt our anonymity. */
        return 0;
      }
    }
    if (exitrouter && !connection_ap_can_use_exit(conn, exitrouter)) {
      /* can't exit from this router */
      return 0;
    }
  } else { /* not general */
    if (rend_cmp_service_ids(conn->rend_query,
                             TO_ORIGIN_CIRCUIT(circ)->rend_query)) {
      /* this circ is not for this conn */
      return 0;
    }
  }
  return 1;
}

/** Return 1 if circuit <b>a</b> is better than circuit <b>b</b> for
 * <b>purpose</b>, and return 0 otherwise. Used by circuit_get_best.
 */
static int
circuit_is_better(circuit_t *a, circuit_t *b, uint8_t purpose)
{
  switch (purpose) {
    case CIRCUIT_PURPOSE_C_GENERAL:
      /* if it's used but less dirty it's best;
       * else if it's more recently created it's best
       */
      if (b->timestamp_dirty) {
        if (a->timestamp_dirty &&
            a->timestamp_dirty > b->timestamp_dirty)
          return 1;
      } else {
        if (a->timestamp_dirty ||
            a->timestamp_created > b->timestamp_created)
          return 1;
        if (CIRCUIT_IS_ORIGIN(b) &&
            TO_ORIGIN_CIRCUIT(b)->build_state->is_internal)
          return 1;
      }
      break;
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
      /* the closer it is to ack_wait the better it is */
      if (a->purpose > b->purpose)
        return 1;
      break;
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      /* the closer it is to rend_joined the better it is */
      if (a->purpose > b->purpose)
        return 1;
      break;
  }
  return 0;
}

/** Find the best circ that conn can use, preferably one which is
 * dirty. Circ must not be too old.
 *
 * Conn must be defined.
 *
 * If must_be_open, ignore circs not in CIRCUIT_STATE_OPEN.
 *
 * circ_purpose specifies what sort of circuit we must have.
 * It can be C_GENERAL, C_INTRODUCE_ACK_WAIT, or C_REND_JOINED.
 *
 * If it's REND_JOINED and must_be_open==0, then return the closest
 * rendezvous-purposed circuit that you can find.
 *
 * If it's INTRODUCE_ACK_WAIT and must_be_open==0, then return the
 * closest introduce-purposed circuit that you can find.
 */
static origin_circuit_t *
circuit_get_best(edge_connection_t *conn, int must_be_open, uint8_t purpose,
                 int need_uptime, int need_internal)
{
  circuit_t *circ, *best=NULL;
  time_t now = time(NULL);

  tor_assert(conn);

  tor_assert(purpose == CIRCUIT_PURPOSE_C_GENERAL ||
             purpose == CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT ||
             purpose == CIRCUIT_PURPOSE_C_REND_JOINED);

  for (circ=global_circuitlist;circ;circ = circ->next) {
    if (!circuit_is_acceptable(circ,conn,must_be_open,purpose,
                               need_uptime,need_internal,now))
      continue;

    /* now this is an acceptable circ to hand back. but that doesn't
     * mean it's the *best* circ to hand back. try to decide.
     */
    if (!best || circuit_is_better(circ,best,purpose))
      best = circ;
  }

  return best ? TO_ORIGIN_CIRCUIT(best) : NULL;
}

/** Close all circuits that start at us, aren't open, and were born
 * at least CircuitBuildTimeout seconds ago.
 */
void
circuit_expire_building(time_t now)
{
  circuit_t *victim, *circ = global_circuitlist;
  time_t cutoff = now - get_options()->CircuitBuildTimeout;
  time_t begindir_cutoff = now - get_options()->CircuitBuildTimeout/2;
  cpath_build_state_t *build_state;

  while (circ) {
    victim = circ;
    circ = circ->next;
    if (!CIRCUIT_IS_ORIGIN(victim) || /* didn't originate here */
        victim->marked_for_close) /* don't mess with marked circs */
      continue;

    build_state = TO_ORIGIN_CIRCUIT(victim)->build_state;
    if (victim->timestamp_created >
        ((build_state && build_state->onehop_tunnel) ?
         begindir_cutoff : cutoff))
      continue; /* it's still young, leave it alone */

#if 0
    /* some debug logs, to help track bugs */
    if (victim->purpose >= CIRCUIT_PURPOSE_C_INTRODUCING &&
        victim->purpose <= CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED) {
      if (!victim->timestamp_dirty)
        log_fn(LOG_DEBUG,"Considering %sopen purp %d to %s (circid %d)."
               "(clean).",
               victim->state == CIRCUIT_STATE_OPEN ? "" : "non",
               victim->purpose, victim->build_state->chosen_exit_name,
               victim->n_circ_id);
      else
        log_fn(LOG_DEBUG,"Considering %sopen purp %d to %s (circid %d). "
               "%d secs since dirty.",
               victim->state == CIRCUIT_STATE_OPEN ? "" : "non",
               victim->purpose, victim->build_state->chosen_exit_name,
               victim->n_circ_id,
               (int)(now - victim->timestamp_dirty));
    }
#endif

    /* if circ is !open, or if it's open but purpose is a non-finished
     * intro or rend, then mark it for close */
    if (victim->state == CIRCUIT_STATE_OPEN) {
      switch (victim->purpose) {
        default: /* most open circuits can be left alone. */
          continue; /* yes, continue inside a switch refers to the nearest
                     * enclosing loop. C is smart. */
        case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
        case CIRCUIT_PURPOSE_C_INTRODUCING:
        case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
          break; /* too old, need to die */
        case CIRCUIT_PURPOSE_C_REND_READY:
          /* it's a rend_ready circ -- has it already picked a query? */
          /* c_rend_ready circs measure age since timestamp_dirty,
           * because that's set when they switch purposes
           */
          if (TO_ORIGIN_CIRCUIT(victim)->rend_query[0] ||
              victim->timestamp_dirty > cutoff)
            continue;
          break;
        case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
        case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
          /* rend and intro circs become dirty each time they
           * make an introduction attempt. so timestamp_dirty
           * will reflect the time since the last attempt.
           */
          if (victim->timestamp_dirty > cutoff)
            continue;
          break;
      }
    }

    if (victim->n_conn)
      log_info(LD_CIRC,"Abandoning circ %s:%d:%d (state %d:%s, purpose %d)",
               victim->n_conn->_base.address, victim->n_port,
               victim->n_circ_id,
               victim->state, circuit_state_to_string(victim->state),
               victim->purpose);
    else
      log_info(LD_CIRC,"Abandoning circ %d (state %d:%s, purpose %d)",
               victim->n_circ_id, victim->state,
               circuit_state_to_string(victim->state), victim->purpose);

    circuit_log_path(LOG_INFO,LD_CIRC,TO_ORIGIN_CIRCUIT(victim));
    circuit_mark_for_close(victim, END_CIRC_REASON_TIMEOUT);
  }
}

/** Remove any elements in <b>needed_ports</b> that are handled by an
 * open or in-progress circuit.
 */
void
circuit_remove_handled_ports(smartlist_t *needed_ports)
{
  int i;
  uint16_t *port;

  for (i = 0; i < smartlist_len(needed_ports); ++i) {
    port = smartlist_get(needed_ports, i);
    tor_assert(*port);
    if (circuit_stream_is_being_handled(NULL, *port,
                                        MIN_CIRCUITS_HANDLING_STREAM)) {
//      log_debug(LD_CIRC,"Port %d is already being handled; removing.", port);
      smartlist_del(needed_ports, i--);
      tor_free(port);
    } else {
      log_debug(LD_CIRC,"Port %d is not handled.", *port);
    }
  }
}

/** Return 1 if at least <b>min</b> general-purpose non-internal circuits
 * will have an acceptable exit node for exit stream <b>conn</b> if it
 * is defined, else for "*:port".
 * Else return 0.
 */
int
circuit_stream_is_being_handled(edge_connection_t *conn,
                                uint16_t port, int min)
{
  circuit_t *circ;
  routerinfo_t *exitrouter;
  int num=0;
  time_t now = time(NULL);
  int need_uptime = smartlist_string_num_isin(get_options()->LongLivedPorts,
                                   conn ? conn->socks_request->port : port);

  for (circ=global_circuitlist;circ;circ = circ->next) {
    if (CIRCUIT_IS_ORIGIN(circ) &&
        !circ->marked_for_close &&
        circ->purpose == CIRCUIT_PURPOSE_C_GENERAL &&
        (!circ->timestamp_dirty ||
         circ->timestamp_dirty + get_options()->MaxCircuitDirtiness > now)) {
      cpath_build_state_t *build_state = TO_ORIGIN_CIRCUIT(circ)->build_state;
      if (build_state->is_internal || build_state->onehop_tunnel)
        continue;

      exitrouter = build_state_get_exit_router(build_state);
      if (exitrouter && (!need_uptime || build_state->need_uptime)) {
        int ok;
        if (conn) {
          ok = connection_ap_can_use_exit(conn, exitrouter);
        } else {
          addr_policy_result_t r = compare_addr_to_addr_policy(
              0, port, exitrouter->exit_policy);
          ok = r != ADDR_POLICY_REJECTED && r != ADDR_POLICY_PROBABLY_REJECTED;
        }
        if (ok) {
          if (++num >= min)
            return 1;
        }