tor/src/or/ext_orport.c

/* Copyright (c) 2012, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file ext_orport.c
 * \brief Code implementing the Extended ORPort.
*/

#include "or.h"
#include "connection.h"
#include "connection_or.h"
#include "ext_orport.h"
#include "control.h"
#include "config.h"
#include "util.h"
#include "main.h"

/** Allocate and return a structure capable of holding an Extended
 *  ORPort message of body length <b>len</b>. */
ext_or_cmd_t *
ext_or_cmd_new(uint16_t len)
{
  size_t size = STRUCT_OFFSET(ext_or_cmd_t, body) + len;
  ext_or_cmd_t *cmd = tor_malloc(size);
  cmd->len = len;
  return cmd;
}

/** Deallocate the Extended ORPort message in <b>cmd</b>. */
void
ext_or_cmd_free(ext_or_cmd_t *cmd)
{
  tor_free(cmd);
}

/** Get an Extended ORPort message from <b>conn</b>, and place it in
 *  <b>out</b>. Return -1 on fail, 0 if we need more data, and 1 if we
 *  successfully extracted an Extended ORPort command from the
 *  buffer.  */
static int
connection_fetch_ext_or_cmd_from_buf(connection_t *conn, ext_or_cmd_t **out)
{
  IF_HAS_BUFFEREVENT(conn, {
    struct evbuffer *input = bufferevent_get_input(conn->bufev);
    return fetch_ext_or_command_from_evbuffer(input, out);
  }) ELSE_IF_NO_BUFFEREVENT {
    return fetch_ext_or_command_from_buf(conn->inbuf, out);
  }
}

/** Write an Extended ORPort message to <b>conn</b>. Use
 *  <b>command</b> as the command type, <b>bodylen</b> as the body
 *  length, and <b>body</b>, if it's present, as the body of the
 *  message. */
static int
connection_write_ext_or_command(connection_t *conn,
                                uint16_t command,
                                const char *body,
                                size_t bodylen)
{
  char header[4];
  if (bodylen > UINT16_MAX)
    return -1;
  set_uint16(header, htons(command));
  set_uint16(header+2, htons(bodylen));
  connection_write_to_buf(header, 4, conn);
  if (bodylen) {
    tor_assert(body);
    connection_write_to_buf(body, bodylen, conn);
  }
  return 0;
}

/** Transition from an Extended ORPort which accepts Extended ORPort
 *  messages, to an Extended ORport which accepts OR traffic. */
static void
connection_ext_or_transition(or_connection_t *conn)
{
  tor_assert(conn->base_.type == CONN_TYPE_EXT_OR);

  conn->base_.type = CONN_TYPE_OR;
  control_event_or_conn_status(conn, OR_CONN_EVENT_NEW, 0);
  connection_tls_start_handshake(conn, 1);
}

/** Length of authentication cookie. */
#define EXT_OR_PORT_AUTH_COOKIE_LEN 32
/** Length of the header of the cookie file. */
#define EXT_OR_PORT_AUTH_COOKIE_HEADER_LEN 32
/** Total length of the cookie file. */
#define EXT_OR_PORT_AUTH_COOKIE_FILE_LEN \
  EXT_OR_PORT_AUTH_COOKIE_LEN+EXT_OR_PORT_AUTH_COOKIE_HEADER_LEN
/** Static cookie file header. */
#define EXT_OR_PORT_AUTH_COOKIE_HEADER "! Extended ORPort Auth Cookie !\x0a"
/** Length of safe-cookie protocol hashes. */
#define EXT_OR_PORT_AUTH_HASH_LEN DIGEST256_LEN
/** Length of safe-cookie protocol nonces. */
#define EXT_OR_PORT_AUTH_NONCE_LEN 32
/** Safe-cookie protocol constants. */
#define EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST \
  "ExtORPort authentication server-to-client hash"
#define EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST \
  "ExtORPort authentication client-to-server hash"

/** If true, we've set ext_or_auth_cookie to a secret code and stored
 * it to disk. */
static int ext_or_auth_cookie_is_set = 0;
/** If ext_or_auth_cookie_is_set, a secret cookie that we've stored to disk
 * and which we're using to authenticate controllers.  (If the controller can
 * read it off disk, it has permission to connect.) */
static char ext_or_auth_cookie[EXT_OR_PORT_AUTH_COOKIE_LEN] = {0};

/** Helper: Return a newly allocated string containing a path to the
 * file where we store our authentication cookie. */
char *
get_ext_or_auth_cookie_file_name(void)
{
  const or_options_t *options = get_options();
  if (options->ExtORPortCookieAuthFile &&
      strlen(options->ExtORPortCookieAuthFile)) {
    return tor_strdup(options->ExtORPortCookieAuthFile);
  } else {
    return get_datadir_fname("extended_orport_auth_cookie");
  }
}

/** Choose a random authentication cookie and write it to disk.
 * Anybody who can read the cookie from disk will be considered
 * authorized to use the control connection. Return -1 if we can't
 * write the file, or 0 on success. */
int
init_ext_or_cookie_authentication(int is_enabled)
{
  char *fname;
  char cookie_file_string[EXT_OR_PORT_AUTH_COOKIE_FILE_LEN];

  if (!is_enabled) {
    ext_or_auth_cookie_is_set = 0;
    return 0;
  }

  /* We don't want to generate a new cookie every time we call
   * options_act(). One should be enough. */
  if (ext_or_auth_cookie_is_set)
    return 0; /* all set */

  if (crypto_rand(ext_or_auth_cookie, EXT_OR_PORT_AUTH_COOKIE_LEN) < 0)
    return -1;
  ext_or_auth_cookie_is_set = 1;

  memcpy(cookie_file_string, EXT_OR_PORT_AUTH_COOKIE_HEADER,
         EXT_OR_PORT_AUTH_COOKIE_HEADER_LEN);
  memcpy(cookie_file_string+EXT_OR_PORT_AUTH_COOKIE_HEADER_LEN,
         ext_or_auth_cookie, EXT_OR_PORT_AUTH_COOKIE_LEN);

  fname = get_ext_or_auth_cookie_file_name();
  if (write_bytes_to_file(fname, cookie_file_string,
                          EXT_OR_PORT_AUTH_COOKIE_FILE_LEN, 1)) {
    log_warn(LD_FS,"Error writing authentication cookie to %s.",
             escaped(fname));
    tor_free(fname);
    return -1;
  }

  log_info(LD_GENERAL, "Generated Extended ORPort cookie file in '%s'.",
           fname);

  memwipe(cookie_file_string, 0, sizeof(cookie_file_string));
  tor_free(fname);
  return 0;
}

/** Read data from <b>conn</b> and see if the client sent us the
 *  authentication type that she prefers to use in this session.
 *
 *  Return -1 if we received corrupted data or if we don't support the
 *  authentication type. Return 0 if we need more data in
 *  <b>conn</b>. Return 1 if the authentication type negotiation was
 *  successful. */
static int
connection_ext_or_auth_neg_auth_type(connection_t *conn)
{
  char authtype[1] = {0};

  if (connection_get_inbuf_len(conn) < 1)
    return 0;

  if (connection_fetch_from_buf(authtype, 1, conn) < 0)
    return -1;

  log_debug(LD_GENERAL, "Client wants us to use %d auth type", authtype[0]);
  if (authtype[0] != 1) /* '1' is the only auth type supported atm */
    return -1;

  conn->state = EXT_OR_CONN_STATE_AUTH_WAIT_CLIENT_NONCE;
  return 1;
}

/** Read the client's nonce out of <b>conn</b>, setup the safe-cookie
 *  crypto, and then send our own hash and nonce to the client
 *
 *  Return -1 if there was an error; return 0 if we need more data in
 *  <b>conn</b>, and return 1 if we successfully retrieved the
 *  client's nonce and sent our own. */
static int
connection_ext_or_auth_handle_client_nonce(connection_t *conn)
{
  char server_hash[EXT_OR_PORT_AUTH_HASH_LEN] = {0};
  char client_nonce[EXT_OR_PORT_AUTH_NONCE_LEN] = {0};
  char server_nonce[EXT_OR_PORT_AUTH_NONCE_LEN] = {0};
  char reply[EXT_OR_PORT_AUTH_COOKIE_LEN+EXT_OR_PORT_AUTH_NONCE_LEN] = {0};

  if (!ext_or_auth_cookie_is_set) { /* this should not happen */
    log_warn(LD_BUG, "Extended ORPort authentication cookie was not set. "
             "That's weird since we should have done that on startup. "
             "This might be a Tor bug, please file a bug report. ");
    return -1;
  }

  if (connection_get_inbuf_len(conn) < EXT_OR_PORT_AUTH_NONCE_LEN)
    return 0;

  if (connection_fetch_from_buf(client_nonce,
                                EXT_OR_PORT_AUTH_NONCE_LEN, conn) < 0)
    return -1;

  /* DOCDOC comment this function more, with comments about what the
   * protocol is. */

  /* Get our nonce */
  if (crypto_rand(server_nonce, EXT_OR_PORT_AUTH_NONCE_LEN) < 0)
    return -1;

  { /* set up macs */
    size_t hmac_s_msg_len = strlen(EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST) +
      2*EXT_OR_PORT_AUTH_NONCE_LEN;
    size_t hmac_c_msg_len = strlen(EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST) +
      2*EXT_OR_PORT_AUTH_NONCE_LEN;

    char *hmac_s_msg = tor_malloc_zero(hmac_s_msg_len);
    char *hmac_c_msg = tor_malloc_zero(hmac_c_msg_len);
    char *correct_client_hash = tor_malloc_zero(EXT_OR_PORT_AUTH_HASH_LEN);

    memcpy(hmac_s_msg,
           EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST,
           strlen(EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST));
    memcpy(hmac_s_msg + strlen(EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST),
           client_nonce, EXT_OR_PORT_AUTH_NONCE_LEN);
    memcpy(hmac_s_msg + strlen(EXT_OR_PORT_AUTH_SERVER_TO_CLIENT_CONST) +
           EXT_OR_PORT_AUTH_NONCE_LEN,
           server_nonce, EXT_OR_PORT_AUTH_NONCE_LEN);

    memcpy(hmac_c_msg,
           EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST,
           strlen(EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST));
    memcpy(hmac_c_msg + strlen(EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST),
           client_nonce, EXT_OR_PORT_AUTH_NONCE_LEN);
    memcpy(hmac_c_msg + strlen(EXT_OR_PORT_AUTH_CLIENT_TO_SERVER_CONST) +
           EXT_OR_PORT_AUTH_NONCE_LEN,
           server_nonce, EXT_OR_PORT_AUTH_NONCE_LEN);

    crypto_hmac_sha256(server_hash,
                       ext_or_auth_cookie,
                       EXT_OR_PORT_AUTH_COOKIE_LEN,
                       hmac_s_msg,
                       hmac_s_msg_len);

    crypto_hmac_sha256(correct_client_hash,
                       ext_or_auth_cookie,
                       EXT_OR_PORT_AUTH_COOKIE_LEN,
                       hmac_c_msg,
                       hmac_c_msg_len);

    /* Store the client hash we generated. We will need to compare it
       with the hash sent by the client. */
    TO_OR_CONN(conn)->ext_or_auth_correct_client_hash = correct_client_hash;

    memwipe(hmac_s_msg, 0, hmac_s_msg_len);
    memwipe(hmac_c_msg, 0, hmac_c_msg_len);

    tor_free(hmac_s_msg);
    tor_free(hmac_c_msg);
  }

  { /* debug logging */ /* XXX disable this codepath if not logging on debug?*/
    char server_hash_encoded[(2*EXT_OR_PORT_AUTH_HASH_LEN) + 1];
    char server_nonce_encoded[(2*EXT_OR_PORT_AUTH_NONCE_LEN) + 1];
    char client_nonce_encoded[(2*EXT_OR_PORT_AUTH_NONCE_LEN) + 1];

    base16_encode(server_hash_encoded, sizeof(server_hash_encoded),
                  server_hash, sizeof(server_hash));
    base16_encode(server_nonce_encoded, sizeof(server_nonce_encoded),
                  server_nonce, sizeof(server_nonce));
    base16_encode(client_nonce_encoded, sizeof(client_nonce_encoded),
                  client_nonce, sizeof(client_nonce));

    log_debug(LD_GENERAL,
              "server_hash: '%s'\nserver_nonce: '%s'\nclient_nonce: '%s'",
              server_hash_encoded, server_nonce_encoded, client_nonce_encoded);

    memwipe(server_hash_encoded, 0, sizeof(server_hash_encoded));
    memwipe(server_nonce_encoded, 0, sizeof(server_nonce_encoded));
    memwipe(client_nonce_encoded, 0, sizeof(client_nonce_encoded));
  }

  { /* write reply: (server_hash, server_nonce) */
    memcpy(reply, server_hash, EXT_OR_PORT_AUTH_HASH_LEN);
    memcpy(reply + EXT_OR_PORT_AUTH_HASH_LEN, server_nonce,
           EXT_OR_PORT_AUTH_NONCE_LEN);
    connection_write_to_buf(reply, sizeof(reply), conn);
    memwipe(reply, 0, sizeof(reply));
  }

  log_debug(LD_GENERAL, "Got client nonce, and sent our own nonce and hash.");

  conn->state = EXT_OR_CONN_STATE_AUTH_WAIT_CLIENT_HASH;
  return 1;
}

#define connection_ext_or_auth_send_result_success(c)  \
  connection_ext_or_auth_send_result(c, 1)
#define connection_ext_or_auth_send_result_fail(c)  \
  connection_ext_or_auth_send_result(c, 0)

/** Send authentication results to <b>conn</b>. Successful results if
 *  <b>success</b> is set; failure results otherwise. */
static void
connection_ext_or_auth_send_result(connection_t *conn, int success)
{
  if (success)
    connection_write_to_buf("\x01", 1, conn);
  else
    connection_write_to_buf("\x00", 1, conn);
}

/** Receive the client's hash from <b>conn</b>, validate that it's
 *  correct, and then send the authentication results to the client.
 *
 *  Return -1 if there was an error during validation; return 0 if we
 *  need more data in <b>conn</b>, and return 1 if we successfully
 *  validated the client's hash and sent a happy authentication
 *  result. */
static int
connection_ext_or_auth_handle_client_hash(connection_t *conn)
{
  char provided_client_hash[EXT_OR_PORT_AUTH_HASH_LEN] = {0};

  if (connection_get_inbuf_len(conn) < EXT_OR_PORT_AUTH_HASH_LEN)
    return 0;

  if (connection_fetch_from_buf(provided_client_hash,
                                EXT_OR_PORT_AUTH_HASH_LEN, conn) < 0)
    return -1;

  if (tor_memneq(TO_OR_CONN(conn)->ext_or_auth_correct_client_hash,
                 provided_client_hash, EXT_OR_PORT_AUTH_HASH_LEN)) {
    log_warn(LD_GENERAL, "Incorrect client hash. Authentication failed.");
    connection_ext_or_auth_send_result_fail(conn);
    return -1;
  }

  log_debug(LD_GENERAL, "Got client's hash and it was legit.");

  /* send positive auth result */
  connection_ext_or_auth_send_result_success(conn);
  conn->state = EXT_OR_CONN_STATE_OPEN;
  return 1;
}

/** Handle data from <b>or_conn</b> received on Extended ORPort.
 *  Return -1 on error. 0 on unsufficient data. 1 on correct. */
static int
connection_ext_or_auth_process_inbuf(or_connection_t *or_conn)
{
  connection_t *conn = TO_CONN(or_conn);

  /* DOCDOC Document the state machine here! */

  switch (conn->state) { /* Functionify */
  case EXT_OR_CONN_STATE_AUTH_WAIT_AUTH_TYPE:
    return connection_ext_or_auth_neg_auth_type(conn);

  case EXT_OR_CONN_STATE_AUTH_WAIT_CLIENT_NONCE:
    return connection_ext_or_auth_handle_client_nonce(conn);

  case EXT_OR_CONN_STATE_AUTH_WAIT_CLIENT_HASH:
    return connection_ext_or_auth_handle_client_hash(conn);

  default:
    log_warn(LD_BUG, "Encountered unexpected connection state %d while trying "
             "to process Extended ORPort authentication data.", conn->state);
    return -1;
  }
}

/** Extended ORPort commands (Transport-to-Bridge) */
#define EXT_OR_CMD_TB_DONE 0x0000
#define EXT_OR_CMD_TB_USERADDR 0x0001
#define EXT_OR_CMD_TB_TRANSPORT 0x0002

/** Extended ORPort commands (Bridge-to-Transport) */
#define EXT_OR_CMD_BT_OKAY 0x1000
#define EXT_OR_CMD_BT_DENY 0x1001
#define EXT_OR_CMD_BT_CONTROL 0x1002

/** Process a USERADDR command from the Extended
 *  ORPort. <b>payload</b> is a payload of size <b>len</b>.
 *
 *  If the USERADDR command was well formed, change the address of
 *  <b>conn</b> to the address on the USERADDR command.
 *
 *  Return 0 on success and -1 on error. */
static int
connection_ext_or_handle_cmd_useraddr(connection_t *conn,
                                      const char *payload, uint16_t len)
{
  /* Copy address string. */
  tor_addr_t addr;
  uint16_t port;
  char *addr_str;
  char *address_part=NULL;
  int res;
  if (memchr(payload, '\0', len)) {
    log_fn(LOG_PROTOCOL_WARN, LD_NET, "Unexpected NUL in ExtORPort UserAddr");
    return -1;
  }

  addr_str = tor_memdup_nulterm(payload, len);

  res = tor_addr_port_split(LOG_INFO, addr_str, &address_part, &port);
  tor_free(addr_str);
  if (res<0)
    return -1;

  res = tor_addr_parse(&addr, address_part);
  tor_free(address_part);
  if (res<0)
    return -1;

  { /* do some logging */
    char *old_address = tor_dup_addr(&conn->addr);
    char *new_address = tor_dup_addr(&addr);

    log_debug(LD_NET, "Received USERADDR."
             "We rewrite our address from '%s:%u' to '%s:%u'.",
             safe_str(old_address), conn->port, safe_str(new_address), port);

    tor_free(old_address);
    tor_free(new_address);
  }

  /* record the address */
  tor_addr_copy(&conn->addr, &addr);
  conn->port = port;

  return 0;
}

/** Process a TRANSPORT command from the Extended
 *  ORPort. <b>payload</b> is a payload of size <b>len</b>.
 *
 *  If the TRANSPORT command was well formed, register the name of the
 *  transport on <b>conn</b>.
 *
 *  Return 0 on success and -1 on error. */
static int
connection_ext_or_handle_cmd_transport(or_connection_t *conn,
                                       const char *payload, uint16_t len)
{
  char *transport_str = tor_malloc(len + 1); /* NUL-terminate the string */
  memcpy(transport_str, payload, len);
  transport_str[len] = 0;

  /* Transport names MUST be C-identifiers. */
  if (!string_is_C_identifier(transport_str)) {
    tor_free(transport_str);
    return -1;
  }

  /* If ext_or_transport is already occupied (because the PT sent two
   *  TRANSPORT commands), deallocate the old name and keep the new
   *  one */
  if (conn->ext_or_transport)
    tor_free(conn->ext_or_transport);

  conn->ext_or_transport = transport_str;
  return 0;
}

#define EXT_OR_CONN_STATE_IS_AUTHENTICATING(st) \
  ((st) <= EXT_OR_CONN_STATE_AUTH_MAX)

/** Process Extended ORPort messages from <b>or_conn</b>. */
int
connection_ext_or_process_inbuf(or_connection_t *or_conn)
{
  connection_t *conn = TO_CONN(or_conn);
  ext_or_cmd_t *command;
  int r;

  /* DOCDOC Document the state machine and transitions in this function */

  /* If we are still in the authentication stage, process traffic as
     authentication data: */
  while (EXT_OR_CONN_STATE_IS_AUTHENTICATING(conn->state)) {
    log_debug(LD_GENERAL, "Got Extended ORPort authentication data (%u).",
              (unsigned int) connection_get_inbuf_len(conn));
    r = connection_ext_or_auth_process_inbuf(or_conn);
    if (r < 0) {
      connection_mark_for_close(conn);
      return -1;
    } else if (r == 0) {
      return 0;
    }
    /* if r > 0, loop and process more data (if any). */
  }

  while (1) {
    log_debug(LD_GENERAL, "Got Extended ORPort data.");
    command = NULL;
    r = connection_fetch_ext_or_cmd_from_buf(conn, &command);
    if (r < 0)
      goto err;
    else if (r == 0)
      return 0; /* need to wait for more data */

    /* Got a command! */
    tor_assert(command);

    if (command->cmd == EXT_OR_CMD_TB_DONE) {
      if (connection_get_inbuf_len(conn)) {
        /* The inbuf isn't empty; the client is misbehaving. */
        goto err;
      }

      log_debug(LD_NET, "Received DONE.");

      /* If the transport proxy did not use the TRANSPORT command to
       * specify the transport name, mark this as unknown transport. */
      if (!or_conn->ext_or_transport) {
        /* We write this string this way to avoid ??>, which is a C
         * trigraph. */
        or_conn->ext_or_transport = tor_strdup("<?" "?>");
      }

      connection_write_ext_or_command(conn, EXT_OR_CMD_BT_OKAY, NULL, 0);

      /* can't transition immediately; need to flush first. */
      conn->state = EXT_OR_CONN_STATE_FLUSHING;
      connection_stop_reading(conn);
    } else if (command->cmd == EXT_OR_CMD_TB_USERADDR) {
      if (connection_ext_or_handle_cmd_useraddr(conn,
                                            command->body, command->len) < 0)
        goto err;
    } else if (command->cmd == EXT_OR_CMD_TB_TRANSPORT) {
      if (connection_ext_or_handle_cmd_transport(or_conn,
                                             command->body, command->len) < 0)
        goto err;
    } else {
      log_notice(LD_NET,"Got Extended ORPort command we don't regognize (%u).",
                 command->cmd);
    }

    ext_or_cmd_free(command);
  }

  return 0;

 err:
  ext_or_cmd_free(command);
  connection_mark_for_close(conn);
  return -1;
}

/** <b>conn</b> finished flushing Extended ORPort messages to the
 *  network, and is now ready to accept OR traffic. This function
 *  does the transition. */
int
connection_ext_or_finished_flushing(or_connection_t *conn)
{
  if (conn->base_.state == EXT_OR_CONN_STATE_FLUSHING) {
    connection_start_reading(TO_CONN(conn));
    connection_ext_or_transition(conn);
  }
  return 0;
}

/** Initiate Extended ORPort authentication, by sending the list of
 *  supported authentication types to the client. */
int
connection_ext_or_start_auth(or_connection_t *or_conn)
{
  connection_t *conn = TO_CONN(or_conn);
  char authtypes[2] = "\x01\x00"; /* We only support authtype '1' for now. */

  log_debug(LD_GENERAL,
           "ExtORPort authentication: Sending supported authentication types");

  connection_write_to_buf(authtypes, sizeof(authtypes), conn);
  conn->state = EXT_OR_CONN_STATE_AUTH_WAIT_AUTH_TYPE;

  return 0;
}