circuitbuild.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 circuitbuild_c_id[] =
  "$Id$";

/**
 * \file circuitbuild.c
 * \brief The actual details of building circuits.
 **/

#include "or.h"

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

/** A global list of all circuits at this hop. */
extern circuit_t *global_circuitlist;

/** An entry_guard_t represents our information about a chosen long-term
 * first hop, known as a "helper" node in the literature. We can't just
 * use a routerinfo_t, since we want to remember these even when we
 * don't have a directory. */
typedef struct {
  char nickname[MAX_NICKNAME_LEN+1];
  char identity[DIGEST_LEN];
  time_t chosen_on_date; /**< Approximately when was this guard added?
                          * "0" if we don't know. */
  char *chosen_by_version; /**< What tor version added this guard? NULL
                            * if we don't know. */
  unsigned int made_contact : 1; /**< 0 if we have never connected to this
                                  * router, 1 if we have. */
  unsigned int can_retry : 1; /**< Should we retry connecting to this entry,
                               * in spite of having it marked as unreachable?*/
  time_t bad_since; /**< 0 if this guard is currently usable, or the time at
                      * which it was observed to become (according to the
                      * directory or the user configuration) unusable. */
  time_t unreachable_since; /**< 0 if we can connect to this guard, or the
                             * time at which we first noticed we couldn't
                             * connect to it. */
  time_t last_attempted; /**< 0 if we can connect to this guard, or the time
                          * at which we last failed to connect to it. */
} entry_guard_t;

/** A list of our chosen entry guards. */
static smartlist_t *entry_guards = NULL;
/** A value of 1 means that the entry_guards list has changed
 * and those changes need to be flushed to disk. */
static int entry_guards_dirty = 0;

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

static int circuit_deliver_create_cell(circuit_t *circ,
                                       uint8_t cell_type, const char *payload);
static int onion_pick_cpath_exit(origin_circuit_t *circ, extend_info_t *exit);
static crypt_path_t *onion_next_hop_in_cpath(crypt_path_t *cpath);
static int onion_extend_cpath(origin_circuit_t *circ);
static int count_acceptable_routers(smartlist_t *routers);
static int onion_append_hop(crypt_path_t **head_ptr, extend_info_t *choice);

static void entry_guards_changed(void);
static time_t start_of_month(time_t when);

/** Iterate over values of circ_id, starting from conn-\>next_circ_id,
 * and with the high bit specified by conn-\>circ_id_type, until we get
 * a circ_id that is not in use by any other circuit on that conn.
 *
 * Return it, or 0 if can't get a unique circ_id.
 */
static uint16_t
get_unique_circ_id_by_conn(or_connection_t *conn)
{
  uint16_t test_circ_id;
  uint16_t attempts=0;
  uint16_t high_bit;

  tor_assert(conn);
  if (conn->circ_id_type == CIRC_ID_TYPE_NEITHER) {
    log_warn(LD_BUG, "Trying to pick a circuit ID for a connection from "
             "a client with no identity.");
    return 0;
  }
  high_bit = (conn->circ_id_type == CIRC_ID_TYPE_HIGHER) ? 1<<15 : 0;
  do {
    /* Sequentially iterate over test_circ_id=1...1<<15-1 until we find a
     * circID such that (high_bit|test_circ_id) is not already used. */
    test_circ_id = conn->next_circ_id++;
    if (test_circ_id == 0 || test_circ_id >= 1<<15) {
      test_circ_id = 1;
      conn->next_circ_id = 2;
    }
    if (++attempts > 1<<15) {
      /* Make sure we don't loop forever if all circ_id's are used. This
       * matters because it's an external DoS opportunity.
       */
      log_warn(LD_CIRC,"No unused circ IDs. Failing.");
      return 0;
    }
    test_circ_id |= high_bit;
  } while (circuit_get_by_circid_orconn(test_circ_id, conn));
  return test_circ_id;
}

/** If <b>verbose</b> is false, allocate and return a comma-separated list of
 * the currently built elements of circuit_t.  If <b>verbose</b> is true, also
 * list information about link status in a more verbose format using spaces.
 * If <b>verbose_names</b> is false, give nicknames for Named routers and hex
 * digests for others; if <b>verbose_names</b> is true, use $DIGEST=Name style
 * names.
 */
static char *
circuit_list_path_impl(origin_circuit_t *circ, int verbose, int verbose_names)
{
  crypt_path_t *hop;
  smartlist_t *elements;
  const char *states[] = {"closed", "waiting for keys", "open"};
  char buf[128];
  char *s;

  elements = smartlist_create();

  if (verbose) {
    const char *nickname = build_state_get_exit_nickname(circ->build_state);
    tor_snprintf(buf, sizeof(buf), "%s%s circ (length %d%s%s):",
                 circ->build_state->is_internal ? "internal" : "exit",
                 circ->build_state->need_uptime ? " (high-uptime)" : "",
                 circ->build_state->desired_path_len,
                 circ->_base.state == CIRCUIT_STATE_OPEN ? "" : ", exit ",
                 circ->_base.state == CIRCUIT_STATE_OPEN ? "" :
                 (nickname?nickname:"*unnamed*"));
    smartlist_add(elements, tor_strdup(buf));
  }

  hop = circ->cpath;
  do {
    routerinfo_t *ri;
    char *elt;
    if (!hop)
      break;
    if (!verbose && hop->state != CPATH_STATE_OPEN)
      break;
    if (!hop->extend_info)
      break;
    if (verbose_names) {
      elt = tor_malloc(MAX_VERBOSE_NICKNAME_LEN+1);
      if ((ri = router_get_by_digest(hop->extend_info->identity_digest))) {
        router_get_verbose_nickname(elt, ri);
      } else if (hop->extend_info->nickname &&
                 is_legal_nickname(hop->extend_info->nickname)) {
        elt[0] = '$';
        base16_encode(elt+1, HEX_DIGEST_LEN+1,
                      hop->extend_info->identity_digest, DIGEST_LEN);
        elt[HEX_DIGEST_LEN+1]= '~';
        strlcpy(elt+HEX_DIGEST_LEN+2,
                hop->extend_info->nickname, MAX_NICKNAME_LEN+1);
      } else {
        elt[0] = '$';
        base16_encode(elt+1, HEX_DIGEST_LEN+1,
                      hop->extend_info->identity_digest, DIGEST_LEN);
      }
    } else { /* ! verbose_names */
      if ((ri = router_get_by_digest(hop->extend_info->identity_digest)) &&
          ri->is_named) {
        elt = tor_strdup(hop->extend_info->nickname);
      } else {
        elt = tor_malloc(HEX_DIGEST_LEN+2);
        elt[0] = '$';
        base16_encode(elt+1, HEX_DIGEST_LEN+1,
                      hop->extend_info->identity_digest, DIGEST_LEN);
      }
    }
    tor_assert(elt);
    if (verbose) {
      size_t len = strlen(elt)+2+strlen(states[hop->state])+1;
      char *v = tor_malloc(len);
      tor_assert(hop->state <= 2);
      tor_snprintf(v,len,"%s(%s)",elt,states[hop->state]);
      smartlist_add(elements, v);
      tor_free(elt);
    } else {
      smartlist_add(elements, elt);
    }
    hop = hop->next;
  } while (hop != circ->cpath);

  s = smartlist_join_strings(elements, verbose?" ":",", 0, NULL);
  SMARTLIST_FOREACH(elements, char*, cp, tor_free(cp));
  smartlist_free(elements);
  return s;
}

/** If <b>verbose</b> is false, allocate and return a comma-separated
 * list of the currently built elements of circuit_t.  If
 * <b>verbose</b> is true, also list information about link status in
 * a more verbose format using spaces.
 */
char *
circuit_list_path(origin_circuit_t *circ, int verbose)
{
  return circuit_list_path_impl(circ, verbose, 0);
}

/** Allocate and return a comma-separated list of the currently built elements
 * of circuit_t, giving each as a verbose nickname.
 */
char *
circuit_list_path_for_controller(origin_circuit_t *circ)
{
  return circuit_list_path_impl(circ, 0, 1);
}

/** Log, at severity <b>severity</b>, the nicknames of each router in
 * circ's cpath. Also log the length of the cpath, and the intended
 * exit point.
 */
void
circuit_log_path(int severity, unsigned int domain, origin_circuit_t *circ)
{
  char *s = circuit_list_path(circ,1);
  log(severity,domain,"%s",s);
  tor_free(s);
}

/** Tell the rep(utation)hist(ory) module about the status of the links
 * in circ.  Hops that have become OPEN are marked as successfully
 * extended; the _first_ hop that isn't open (if any) is marked as
 * unable to extend.
 */
/* XXXX Someday we should learn from OR circuits too. */
void
circuit_rep_hist_note_result(origin_circuit_t *circ)
{
  crypt_path_t *hop;
  char *prev_digest = NULL;
  routerinfo_t *router;
  hop = circ->cpath;
  if (!hop) /* circuit hasn't started building yet. */
    return;
  if (server_mode(get_options())) {
    routerinfo_t *me = router_get_my_routerinfo();
    if (!me)
      return;
    prev_digest = me->cache_info.identity_digest;
  }
  do {
    router = router_get_by_digest(hop->extend_info->identity_digest);
    if (router) {
      if (prev_digest) {
        if (hop->state == CPATH_STATE_OPEN)
          rep_hist_note_extend_succeeded(prev_digest,
                                         router->cache_info.identity_digest);
        else {
          rep_hist_note_extend_failed(prev_digest,
                                      router->cache_info.identity_digest);
          break;
        }
      }
      prev_digest = router->cache_info.identity_digest;
    } else {
      prev_digest = NULL;
    }
    hop=hop->next;
  } while (hop!=circ->cpath);
}

/** Pick all the entries in our cpath. Stop and return 0 when we're
 * happy, or return -1 if an error occurs. */
static int
onion_populate_cpath(origin_circuit_t *circ)
{
  int r;
again:
  r = onion_extend_cpath(circ);
  if (r < 0) {
    log_info(LD_CIRC,"Generating cpath hop failed.");
    return -1;
  }
  if (r == 0)
    goto again;
  return 0; /* if r == 1 */
}

/** Create and return a new origin circuit. Initialize its purpose and
 * build-state based on our arguments.  The <b>flags</b> argument is a
 * bitfield of CIRCLAUNCH_* flags. */
origin_circuit_t *
origin_circuit_init(uint8_t purpose, int flags)
{
  /* sets circ->p_circ_id and circ->p_conn */
  origin_circuit_t *circ = origin_circuit_new();
  circuit_set_state(TO_CIRCUIT(circ), CIRCUIT_STATE_OR_WAIT);
  circ->build_state = tor_malloc_zero(sizeof(cpath_build_state_t));
  circ->build_state->onehop_tunnel =
    ((flags & CIRCLAUNCH_ONEHOP_TUNNEL) ? 1 : 0);
  circ->build_state->need_uptime =
    ((flags & CIRCLAUNCH_NEED_UPTIME) ? 1 : 0);
  circ->build_state->need_capacity =
    ((flags & CIRCLAUNCH_NEED_CAPACITY) ? 1 : 0);
  circ->build_state->is_internal =
    ((flags & CIRCLAUNCH_IS_INTERNAL) ? 1 : 0);
  circ->_base.purpose = purpose;
  return circ;
}

/** Build a new circuit for <b>purpose</b>. If <b>exit</b>
 * is defined, then use that as your exit router, else choose a suitable
 * exit node.
 *
 * Also launch a connection to the first OR in the chosen path, if
 * it's not open already.
 */
origin_circuit_t *
circuit_establish_circuit(uint8_t purpose, extend_info_t *exit, int flags)
{
  origin_circuit_t *circ;
  int err_reason = 0;

  circ = origin_circuit_init(purpose, flags);

  if (onion_pick_cpath_exit(circ, exit) < 0 ||
      onion_populate_cpath(circ) < 0) {
    circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_NOPATH);
    return NULL;
  }

  control_event_circuit_status(circ, CIRC_EVENT_LAUNCHED, 0);

  if ((err_reason = circuit_handle_first_hop(circ)) < 0) {
    circuit_mark_for_close(TO_CIRCUIT(circ), -err_reason);
    return NULL;
  }
  return circ;
}

/** Start establishing the first hop of our circuit. Figure out what
 * OR we should connect to, and if necessary start the connection to
 * it. If we're already connected, then send the 'create' cell.
 * Return 0 for ok, -reason if circ should be marked-for-close. */
int
circuit_handle_first_hop(origin_circuit_t *circ)
{
  crypt_path_t *firsthop;
  or_connection_t *n_conn;
  char tmpbuf[INET_NTOA_BUF_LEN];
  struct in_addr in;
  int err_reason = 0;

  firsthop = onion_next_hop_in_cpath(circ->cpath);
  tor_assert(firsthop);
  tor_assert(firsthop->extend_info);

  /* now see if we're already connected to the first OR in 'route' */
  in.s_addr = htonl(firsthop->extend_info->addr);
  tor_inet_ntoa(&in, tmpbuf, sizeof(tmpbuf));
  log_debug(LD_CIRC,"Looking for firsthop '%s:%u'",tmpbuf,
            firsthop->extend_info->port);
  /* imprint the circuit with its future n_conn->id */
  memcpy(circ->_base.n_conn_id_digest, firsthop->extend_info->identity_digest,
         DIGEST_LEN);
  n_conn = connection_or_get_by_identity_digest(
         firsthop->extend_info->identity_digest);
  /* If we don't have an open conn, or the conn we have is obsolete
   * (i.e. old or broken) and the other side will let us make a second
   * connection without dropping it immediately... */
  if (!n_conn || n_conn->_base.state != OR_CONN_STATE_OPEN ||