/*  $OpenBSD: arc4random.c,v 1.54 2015/09/13 08:31:47 guenther Exp $  */

/*

 * SPDX-License-Identifier: ISC

 *

 * Copyright (c) 1996, David Mazieres <dm@uun.org>

 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>

 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>

 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>

 *

 * Permission to use, copy, modify, and distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR

 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN

 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF

 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 */

/*

 * ChaCha based random number generator for OpenBSD.

 */

#include <config.h>

#ifndef HAVE_ARC4RANDOM

#ifdef HAVE_SYS_RANDOM_H

# include <sys/random.h>

#endif

#include <fcntl.h>

#include <limits.h>

#include <signal.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#if defined(HAVE_STDINT_H)

# include <stdint.h>

#elif defined(HAVE_INTTYPES_H)

# include <inttypes.h>

#endif

#include <sudo_compat.h>

#include <sudo_fatal.h>

#include <sudo_rand.h>

#define KEYSTREAM_ONLY

#include "chacha_private.h"

#define minimum(a, b) ((a) < (b) ? (a) : (b))

#ifdef __GNUC__

# define inline __inline

#else       /* !__GNUC__ */

# define inline

#endif        /* !__GNUC__ */

/* Sudo isn't multithreaded */

#define _ARC4_LOCK()

#define _ARC4_UNLOCK()

#define KEYSZ 32

#define IVSZ  8

#define BLOCKSZ 64

#define RSBUFSZ (16*BLOCKSZ)

static int rs_initialized;

static pid_t rs_stir_pid;

static chacha_ctx rs;   /* chacha context for random keystream */

static u_char rs_buf[RSBUFSZ];  /* keystream blocks */

static size_t rs_have;    /* valid bytes at end of rs_buf */

static size_t rs_count;   /* bytes till reseed */

static inline void _rs_rekey(unsigned char *dat, size_t datlen);

static inline void

_rs_init(unsigned char *buf, size_t n)

{

  if (n < KEYSZ + IVSZ)

    return;

  chacha_keysetup(&rs, buf, KEYSZ * 8, 0);

  chacha_ivsetup(&rs, buf + KEYSZ);

}

static void

_rs_stir(void)

{

  unsigned char rnd[KEYSZ + IVSZ];

  if (getentropy(rnd, sizeof rnd) == -1)

    sudo_fatal_nodebug("getentropy");

  if (!rs_initialized) {

    rs_initialized = 1;

    _rs_init(rnd, sizeof(rnd));

  } else

    _rs_rekey(rnd, sizeof(rnd));

  explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */

  /* invalidate rs_buf */

  rs_have = 0;

  memset(rs_buf, 0, sizeof(rs_buf));

  rs_count = 1600000;

}

static inline void

_rs_stir_if_needed(size_t len)

{

  pid_t pid = getpid();

  if (rs_count <= len || !rs_initialized || rs_stir_pid != pid) {

    rs_stir_pid = pid;

    _rs_stir();

  } else

    rs_count -= len;

}

static inline void

_rs_rekey(unsigned char *dat, size_t datlen)

{

#ifndef KEYSTREAM_ONLY

  memset(rs_buf, 0, sizeof(rs_buf));

#endif

  /* fill rs_buf with the keystream */

  chacha_encrypt_bytes(&rs, rs_buf, rs_buf, sizeof(rs_buf));

  /* mix in optional user provided data */

  if (dat) {

    size_t i, m;

    m = minimum(datlen, KEYSZ + IVSZ);

    for (i = 0; i < m; i++)

      rs_buf[i] ^= dat[i];

  }

  /* immediately reinit for backtracking resistance */

  _rs_init(rs_buf, KEYSZ + IVSZ);

  memset(rs_buf, 0, KEYSZ + IVSZ); // -V::512, 1086

  rs_have = sizeof(rs_buf) - KEYSZ - IVSZ;

}

static inline void

_rs_random_buf(void *_buf, size_t n)

{

  unsigned char *buf = _buf;

  unsigned char *keystream;

  size_t m;

  _rs_stir_if_needed(n);

  while (n > 0) {

    if (rs_have > 0) {

      m = minimum(n, rs_have);

      keystream = rs_buf + sizeof(rs_buf) - rs_have;

      memcpy(buf, keystream, m);

      memset(keystream, 0, m);

      buf += m;

      n -= m;

      rs_have -= m;

    }

    if (rs_have == 0)

      _rs_rekey(NULL, 0);

  }

}

static inline void

_rs_random_u32(uint32_t *val)

{

  unsigned char *keystream;

  _rs_stir_if_needed(sizeof(*val));

  if (rs_have < sizeof(*val))

    _rs_rekey(NULL, 0);

  keystream = rs_buf + sizeof(rs_buf) - rs_have;

  memcpy(val, keystream, sizeof(*val));

  memset(keystream, 0, sizeof(*val));

  rs_have -= sizeof(*val);

}

uint32_t

sudo_arc4random(void)

{

  uint32_t val;

  _ARC4_LOCK();

  _rs_random_u32(&val);

  _ARC4_UNLOCK();

  return val;

}

void

sudo_arc4random_buf(void *buf, size_t n)

{

  _ARC4_LOCK();

  _rs_random_buf(buf, n);

  _ARC4_UNLOCK();

}

#endif /* HAVE_ARC4RANDOM */