/*

 * Copyright the NTPsec project contributors

 * SPDX-License-Identifier: BSD-2-Clause

 */

#include <stdint.h>

#include <string.h>

#include <openssl/opensslv.h>

#include <openssl/rand.h>

#include "config.h"

#include "ntp.h"

#include "ntp_stdlib.h"

#include "ntp_syslog.h"

#ifndef PRAND_BUF_LEN

#define PRAND_BUF_LEN 4096l

#endif

static uint8_t prand_buffer[PRAND_BUF_LEN];

static size_t prand_burned = PRAND_BUF_LEN;

/* NB: RAND_bytes comes from OpenSSL

 * Starting in version 1.1.1, it reseeds itself occasionally.

 * That may need access to /dev/urandom which may be blocked by chroot jails.

 * getrandom(2) is used when available.  It was added to Linux kernel 3.17

 * so this won't be a problem on newer Linux systems.

 */

/* Use psuedorandom pool to get entropy from */

static void ntp_pool_rand_fill(uint8_t *buf, int num) {

  if (0 > num) {

    return;

  }

  if (1 != RAND_bytes(buf, num)) {

    msyslog(LOG_ERR, "ERR: RAND_bytes failed");

    exit(1);

  }

}

void ntp_RAND_bytes(unsigned char *buf, int num) {

  if (0 >= num) {

    return;

  }

  if (PRAND_BUF_LEN <= num) {  // This should never happen

    return ntp_pool_rand_fill(buf, num);

  }

  if (PRAND_BUF_LEN < num + prand_burned) {

    ntp_pool_rand_fill(prand_buffer, prand_burned);

    prand_burned = 0;

  }

  memcpy(buf, prand_buffer + prand_burned, num);

  prand_burned += num;

}

void ntp_RAND_priv_bytes(unsigned char *buf, int num) {

  int err;

#if (OPENSSL_VERSION_NUMBER > 0x1010100fL) && !defined(LIBRESSL_VERSION_NUMBER)

  err = RAND_priv_bytes(buf, num);

#else

  err = RAND_bytes(buf, num);

#endif

  if (1 != err) {

    msyslog(LOG_ERR, "ERR: RAND_priv_bytes failed");

    exit(1);

  }

}

/* Return four byes of entropy. This differs from the ~31bits from random() */

uint32_t ntp_random(void) {

  uint32_t ret;

  ntp_RAND_bytes((uint8_t*)&ret, sizeof(ret));

  return ret;

}