arc4random.c

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

/*
 * SPDX-License-Identifier: ISC
 *
 * Copyright (c) 1996, David Mazieres <[email protected]>
 * Copyright (c) 2008, Damien Miller <[email protected]>
 * Copyright (c) 2013, Markus Friedl <[email protected]>
 * Copyright (c) 2014, Theo de Raadt <[email protected]>
 *
 * 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 */