crypt_path.c

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/*
 * Copyright (c) 2019-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */
 
/**
 * \file crypt_path.c
 *
 * \brief Functions dealing with layered circuit encryption. This file aims to
 *   provide an API around the crypt_path_t structure which holds crypto
 *   information about a specific hop of a circuit.
 *
 * TODO: We should eventually move all functions dealing and manipulating
 *   crypt_path_t to this file, so that eventually we encapsulate more and more
 *   of crypt_path_t. Here are some more functions that can be moved here with
 *   some more effort:
 *
 *   - circuit_list_path_impl()
 **/
 
#define CRYPT_PATH_PRIVATE
 
#include "core/or/or.h"
#include "core/or/crypt_path.h"
 
#include "core/crypto/relay_crypto.h"
#include "core/crypto/onion_crypto.h"
#include "core/or/circuitbuild.h"
#include "core/or/circuitlist.h"
#include "core/or/extendinfo.h"
#include "core/or/congestion_control_common.h"
 
#include "lib/crypt_ops/crypto_dh.h"
#include "lib/crypt_ops/crypto_util.h"
 
#include "core/or/crypt_path_st.h"
#include "core/or/cell_st.h"
 
/** Add <b>new_hop</b> to the end of the doubly-linked-list <b>head_ptr</b>.
 * This function is used to extend cpath by another hop.
 */
void
cpath_extend_linked_list(crypt_path_t **head_ptr, crypt_path_t *new_hop)
{
  if (*head_ptr) {
    new_hop->next = (*head_ptr);
    new_hop->prev = (*head_ptr)->prev;
    (*head_ptr)->prev->next = new_hop;
    (*head_ptr)->prev = new_hop;
  } else {
    *head_ptr = new_hop;
    new_hop->prev = new_hop->next = new_hop;
  }
}
 
/** Create a new hop, annotate it with information about its
 * corresponding router <b>choice</b>, and append it to the
 * end of the cpath <b>head_ptr</b>. */
int
cpath_append_hop(crypt_path_t **head_ptr, extend_info_t *choice)
{
  crypt_path_t *hop = tor_malloc_zero(sizeof(crypt_path_t));
 
  /* link hop into the cpath, at the end. */
  cpath_extend_linked_list(head_ptr, hop);
 
  hop->magic = CRYPT_PATH_MAGIC;
  hop->state = CPATH_STATE_CLOSED;
 
  hop->extend_info = extend_info_dup(choice);
 
  hop->package_window = circuit_initial_package_window();
  hop->deliver_window = CIRCWINDOW_START;
 
  // This can get changed later on by circuit negotiation.
  hop->relay_cell_format = RELAY_CELL_FORMAT_V0;
 
  return 0;
}
 
/** Verify that cpath <b>cp</b> has all of its invariants
 * correct. Trigger an assert if anything is invalid.
 */
void
cpath_assert_ok(const crypt_path_t *cp)
{
  const crypt_path_t *start = cp;
 
  do {
    cpath_assert_layer_ok(cp);
    /* layers must be in sequence of: "open* awaiting? closed*" */
    if (cp != start) {
      if (cp->state == CPATH_STATE_AWAITING_KEYS) {
        tor_assert(cp->prev->state == CPATH_STATE_OPEN);
      } else if (cp->state == CPATH_STATE_OPEN) {
        tor_assert(cp->prev->state == CPATH_STATE_OPEN);
      }
    }
    cp = cp->next;
    tor_assert(cp);
  } while (cp != start);
}
 
/** Verify that cpath layer <b>cp</b> has all of its invariants
 * correct. Trigger an assert if anything is invalid.
 */
void
cpath_assert_layer_ok(const crypt_path_t *cp)
{
//  tor_assert(cp->addr); /* these are zero for rendezvous extra-hops */
//  tor_assert(cp->port);
  tor_assert(cp);
  tor_assert(cp->magic == CRYPT_PATH_MAGIC);
  switch (cp->state)
    {
    case CPATH_STATE_OPEN:
      relay_crypto_assert_ok(&cp->pvt_crypto);
      FALLTHROUGH;
    case CPATH_STATE_CLOSED:
      break;
    case CPATH_STATE_AWAITING_KEYS:
      break;
    default:
      log_fn(LOG_ERR, LD_BUG, "Unexpected state %d", cp->state);
      tor_assert(0);
    }
  tor_assert(cp->package_window >= 0);
  tor_assert(cp->deliver_window >= 0);
}
 
/** Initialize cpath->{f|b}_{crypto|digest} from the key material in key_data.
 *
 * If <b>is_hs_v3</b> is set, this cpath will be used for next gen hidden
 * service circuits and <b>key_data</b> must be at least
 * HS_NTOR_KEY_EXPANSION_KDF_OUT_LEN bytes in length.
 *
 * If <b>is_hs_v3</b> is not set, key_data must contain CPATH_KEY_MATERIAL_LEN
 * bytes, which are used as follows:
 *   - 20 to initialize f_digest
 *   - 20 to initialize b_digest
 *   - 16 to key f_crypto
 *   - 16 to key b_crypto
 *
 * (If 'reverse' is true, then f_XX and b_XX are swapped.)
 *
 * Return 0 if init was successful, else -1 if it failed.
 */
int
cpath_init_circuit_crypto(relay_crypto_alg_t alg,
                          crypt_path_t *cpath,
                          const char *key_data, size_t key_data_len)
{
 
  tor_assert(cpath);
  return relay_crypto_init(alg, &cpath->pvt_crypto, key_data, key_data_len);
}
 
/** Deallocate space associated with the cpath node <b>victim</b>. */
void
cpath_free(crypt_path_t *victim)
{
  if (!victim)
    return;
 
  relay_crypto_clear(&victim->pvt_crypto);
  onion_handshake_state_release(&victim->handshake_state);
  extend_info_free(victim->extend_info);
  congestion_control_free(victim->ccontrol);
 
  memwipe(victim, 0xBB, sizeof(crypt_path_t)); /* poison memory */
  tor_free(victim);
}
 
/************ cpath sendme API ***************************/
 
/** Return the sendme tag of this <b>cpath</b>,
 * along with its length. */
const uint8_t *
cpath_get_sendme_tag(crypt_path_t *cpath, size_t *len_out)
{
  return relay_crypto_get_sendme_tag(&cpath->pvt_crypto, len_out);
}
 
/************ other cpath functions ***************************/
 
/** Return the first non-open hop in cpath, or return NULL if all
 * hops are open. */
crypt_path_t *
cpath_get_next_non_open_hop(crypt_path_t *cpath)
{
  crypt_path_t *hop = cpath;
  do {
    if (hop->state != CPATH_STATE_OPEN)
      return hop;
    hop = hop->next;
  } while (hop != cpath);
  return NULL;
}
 
#ifdef TOR_UNIT_TESTS
 
/** Unittest helper function: Count number of hops in cpath linked list. */
unsigned int
cpath_get_n_hops(crypt_path_t **head_ptr)
{
  unsigned int n_hops = 0;
  crypt_path_t *tmp;
 
  if (!*head_ptr) {
    return 0;
  }
 
  tmp = *head_ptr;
  do {
    n_hops++;
    tmp = tmp->next;
  } while (tmp != *head_ptr);
 
  return n_hops;
}
 
#endif /* defined(TOR_UNIT_TESTS) */