/*

 * Copyright (C) 2018 Red Hat, Inc.

 *

 * Author: Daiki Ueno

 *

 * This file is part of GnuTLS.

 *

 * The GnuTLS is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public License

 * as published by the Free Software Foundation; either version 2.1 of

 * the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with this program.  If not, see <https://www.gnu.org/licenses/>

 *

 */

#include "gnutls_int.h"

#include "db.h"

#include "system.h"

#include "tls13/anti_replay.h"

/* The default time window in milliseconds; RFC8446 suggests the order

 * of ten seconds is sufficient for the clients on the Internet. */

#define DEFAULT_WINDOW_MS 10000

struct gnutls_anti_replay_st {

  uint32_t window;

  struct timespec start_time;

  gnutls_db_add_func db_add_func;

  void *db_ptr;

};

/**

 * gnutls_anti_replay_init:

 * @anti_replay: is a pointer to #gnutls_anti_replay_t type

 *

 * This function will allocate and initialize the @anti_replay context

 * to be usable for detect replay attacks. The context can then be

 * attached to a @gnutls_session_t with

 * gnutls_anti_replay_enable().

 *

 * Returns: Zero or a negative error code on error.

 *

 * Since: 3.6.5

 **/

int gnutls_anti_replay_init(gnutls_anti_replay_t *anti_replay)

{

  *anti_replay = gnutls_calloc(1, sizeof(struct gnutls_anti_replay_st));

  if (!*anti_replay)

    return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

  (*anti_replay)->window = DEFAULT_WINDOW_MS;

  gnutls_gettime(&(*anti_replay)->start_time);

  return 0;

}

/**

 * gnutls_anti_replay_set_window:

 * @anti_replay: is a #gnutls_anti_replay_t type.

 * @window: is the time window recording ClientHello, in milliseconds

 *

 * Sets the time window used for ClientHello recording.  In order to

 * protect against replay attacks, the server records ClientHello

 * messages within this time period from the last update, and

 * considers it a replay when a ClientHello outside of the period; if

 * a ClientHello arrives within this period, the server checks the

 * database and detects duplicates.

 *

 * For the details of the algorithm, see RFC 8446, section 8.2.

 *

 * Since: 3.6.5

 */

void gnutls_anti_replay_set_window(gnutls_anti_replay_t anti_replay,

           unsigned int window)

{

  anti_replay->window = window;

}

/**

 * gnutls_anti_replay_deinit:

 * @anti_replay: is a #gnutls_anti_replay type

 *

 * This function will deinitialize all resources occupied by the given

 * anti-replay context.

 *

 * Since: 3.6.5

 **/

void gnutls_anti_replay_deinit(gnutls_anti_replay_t anti_replay)

{

  gnutls_free(anti_replay);

}

/**

 * gnutls_anti_replay_enable:

 * @session: is a #gnutls_session_t type.

 * @anti_replay: is a #gnutls_anti_replay_t type.

 *

 * Request that the server should use anti-replay mechanism.

 *

 * Since: 3.6.5

 **/

void gnutls_anti_replay_enable(gnutls_session_t session,

             gnutls_anti_replay_t anti_replay)

{

  if (unlikely(session->security_parameters.entity != GNUTLS_SERVER)) {

    gnutls_assert();

    return;

  }

  session->internals.anti_replay = anti_replay;

}

int _gnutls_anti_replay_check(gnutls_anti_replay_t anti_replay,

            uint32_t client_ticket_age,

            struct timespec *ticket_creation_time,

            gnutls_datum_t *id)

{

  struct timespec now;

  time_t window;

  uint32_t server_ticket_age, diff;

  gnutls_datum_t key = { NULL, 0 };

  gnutls_datum_t entry = { NULL, 0 };

  unsigned char key_buffer[MAX_HASH_SIZE + 12];

  unsigned char entry_buffer[12]; /* magic + timestamp + expire_time */

  unsigned char *p;

  int ret;

  if (unlikely(id->size > MAX_HASH_SIZE))

    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  gnutls_gettime(&now);

  server_ticket_age = timespec_sub_ms(&now, ticket_creation_time);

  /* It shouldn't be possible that the server's view of ticket

   * age is smaller than the client's view.

   */

  if (unlikely(server_ticket_age < client_ticket_age))

    return gnutls_assert_val(GNUTLS_E_ILLEGAL_PARAMETER);

  /* If ticket is created before recording has started, discard

   * reject early data.

   */

  if (_gnutls_timespec_cmp(ticket_creation_time,

         &anti_replay->start_time) < 0) {

    _gnutls_handshake_log(

      "anti_replay: ticket is created before recording has started\n");

    return gnutls_assert_val(GNUTLS_E_EARLY_DATA_REJECTED);

  }

  /* If certain amount of time (window) has elapsed, rollover

   * the recording.

   */

  diff = timespec_sub_ms(&now, &anti_replay->start_time);

  if (diff > anti_replay->window)

    gnutls_gettime(&anti_replay->start_time);

  /* If expected_arrival_time is out of window, reject early

   * data.

   */

  if (server_ticket_age - client_ticket_age > anti_replay->window) {

    _gnutls_handshake_log(

      "anti_replay: server ticket age: %u, client ticket age: %u\n",

      server_ticket_age, client_ticket_age);

    return gnutls_assert_val(GNUTLS_E_EARLY_DATA_REJECTED);

  }

  /* Check if the ClientHello is stored in the database.

   */

  if (!anti_replay->db_add_func)

    return gnutls_assert_val(GNUTLS_E_EARLY_DATA_REJECTED);

  /* Create a key for database lookup, prefixing window start

   * time to ID.  Note that this shouldn't clash with session ID

   * used in TLS 1.2, because such IDs are 32 octets, while here

   * the key becomes 44+ octets.

   */

  p = key_buffer;

  _gnutls_write_uint32((uint64_t)anti_replay->start_time.tv_sec >> 32, p);

  p += 4;

  _gnutls_write_uint32(anti_replay->start_time.tv_sec & 0xFFFFFFFF, p);

  p += 4;

  _gnutls_write_uint32(anti_replay->start_time.tv_nsec, p);

  p += 4;

  memcpy(p, id->data, id->size);

  p += id->size;

  key.data = key_buffer;

  key.size = p - key_buffer;

  /* Create an entry to be stored on database if the lookup

   * failed.  This is formatted so that

   * gnutls_db_check_entry_expire_time() work.

   */

  p = entry_buffer;

  _gnutls_write_uint32(PACKED_SESSION_MAGIC, p);

  p += 4;

  _gnutls_write_uint32(now.tv_sec, p);

  p += 4;

  window = anti_replay->window / 1000;

  _gnutls_write_uint32(window, p);

  p += 4;

  entry.data = entry_buffer;

  entry.size = p - entry_buffer;

  ret = anti_replay->db_add_func(anti_replay->db_ptr,

               (uint64_t)now.tv_sec + (uint64_t)window,

               &key, &entry);

  if (ret < 0) {

    _gnutls_handshake_log(

      "anti_replay: duplicate ClientHello found\n");

    return gnutls_assert_val(GNUTLS_E_EARLY_DATA_REJECTED);

  }

  return 0;

}

/**

 * gnutls_anti_replay_set_ptr:

 * @anti_replay: is a #gnutls_anti_replay_t type.

 * @ptr: is the pointer

 *

 * Sets the pointer that will be provided to db add function

 * as the first argument.

 **/

void gnutls_anti_replay_set_ptr(gnutls_anti_replay_t anti_replay, void *ptr)

{

  anti_replay->db_ptr = ptr;

}

/**

 * gnutls_anti_replay_set_add_function:

 * @anti_replay: is a #gnutls_anti_replay_t type.

 * @add_func: is the function.

 *

 * Sets the function that will be used to store an entry if it is not

 * already present in the resumed sessions database.  This function returns 0

 * if the entry is successfully stored, and a negative error code

 * otherwise.  In particular, if the entry is found in the database,

 * it returns %GNUTLS_E_DB_ENTRY_EXISTS.

 *

 * The arguments to the @add_func are:

 *  - %ptr: the pointer set with gnutls_anti_replay_set_ptr()

 *  - %exp_time: the expiration time of the entry

 *  - %key: a pointer to the key

 *  - %data: a pointer to data to store

 *

 * The data set by this function can be examined using

 * gnutls_db_check_entry_expire_time() and gnutls_db_check_entry_time().

 *

 * Since: 3.6.5

 **/

void gnutls_anti_replay_set_add_function(gnutls_anti_replay_t anti_replay,

           gnutls_db_add_func add_func)

{

  anti_replay->db_add_func = add_func;

}