1/*      $OpenBSD: arc4random.c,v 1.41 2014/07/12 13:24:54 deraadt Exp $ */
2
3/*
4 * Copyright (c) 1996, David Mazieres <dm@uun.org>
5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
6 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
7 *
8 * Permission to use, copy, modify, and distribute this software for any
9 * purpose with or without fee is hereby granted, provided that the above
10 * copyright notice and this permission notice appear in all copies.
11 *
12 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
13 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
14 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
15 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
16 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
17 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
18 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
19 */
20#include "config.h"
21
22/*
23 * ChaCha based random number generator for OpenBSD.
24 */
25
26#include <fcntl.h>
27#include <limits.h>
28#include <signal.h>
29#ifdef HAVE_STDINT_H
30#include <stdint.h>
31#endif
32#include <stdlib.h>
33#include <string.h>
34#include <unistd.h>
35#include <sys/types.h>
36#include <sys/param.h>
37#include <sys/time.h>
38#ifndef UB_ON_WINDOWS
39#include <sys/mman.h>
40#endif
41
42#define KEYSTREAM_ONLY
43#include "chacha_private.h"
44
45#define arc4_min(a, b) ((a) < (b) ? (a) : (b))
46#ifdef __GNUC__
47#define inline __inline
48#else				/* !__GNUC__ */
49#define inline
50#endif				/* !__GNUC__ */
51
52#define KEYSZ	32
53#define IVSZ	8
54#define BLOCKSZ	64
55#define RSBUFSZ	(16*BLOCKSZ)
56
57/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
58static struct {
59	size_t		rs_have;	/* valid bytes at end of rs_buf */
60	size_t		rs_count;	/* bytes till reseed */
61} *rs;
62
63/* Preserved in fork children. */
64static struct {
65	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
66	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
67} *rsx;
68
69static inline void _rs_rekey(u_char *dat, size_t datlen);
70
71static inline void
72_rs_init(u_char *buf, size_t n)
73{
74	if (n < KEYSZ + IVSZ)
75		return;
76
77	if (rs == NULL) {
78#ifndef UB_ON_WINDOWS
79		if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
80		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
81			abort();
82#ifdef MAP_INHERIT_ZERO
83		if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1)
84			abort();
85#endif
86#else /* WINDOWS */
87		rs = malloc(sizeof(*rs));
88		if(!rs)
89			abort();
90#endif
91	}
92	if (rsx == NULL) {
93#ifndef UB_ON_WINDOWS
94		if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE,
95		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
96			abort();
97#else /* WINDOWS */
98		rsx = malloc(sizeof(*rsx));
99		if(!rsx)
100			abort();
101#endif
102	}
103
104	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
105	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
106}
107
108static void
109_rs_stir(void)
110{
111	u_char rnd[KEYSZ + IVSZ];
112
113	if (getentropy(rnd, sizeof rnd) == -1) {
114#ifdef SIGKILL
115		raise(SIGKILL);
116#else
117		exit(9); /* windows */
118#endif
119	}
120
121	if (!rs)
122		_rs_init(rnd, sizeof(rnd));
123	else
124		_rs_rekey(rnd, sizeof(rnd));
125	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
126
127	/* invalidate rs_buf */
128	rs->rs_have = 0;
129	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
130
131	rs->rs_count = 1600000;
132}
133
134static inline void
135_rs_stir_if_needed(size_t len)
136{
137#ifndef MAP_INHERIT_ZERO
138	static pid_t _rs_pid = 0;
139	pid_t pid = getpid();
140
141	/* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */
142	if (_rs_pid == 0 || _rs_pid != pid) {
143		_rs_pid = pid;
144		if (rs)
145			rs->rs_count = 0;
146	}
147#endif
148	if (!rs || rs->rs_count <= len)
149		_rs_stir();
150	if (rs->rs_count <= len)
151		rs->rs_count = 0;
152	else
153		rs->rs_count -= len;
154}
155
156static inline void
157_rs_rekey(u_char *dat, size_t datlen)
158{
159#ifndef KEYSTREAM_ONLY
160	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
161#endif
162	/* fill rs_buf with the keystream */
163	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
164	    rsx->rs_buf, sizeof(rsx->rs_buf));
165	/* mix in optional user provided data */
166	if (dat) {
167		size_t i, m;
168
169		m = arc4_min(datlen, KEYSZ + IVSZ);
170		for (i = 0; i < m; i++)
171			rsx->rs_buf[i] ^= dat[i];
172	}
173	/* immediately reinit for backtracking resistance */
174	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
175	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
176	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
177}
178
179static inline void
180_rs_random_buf(void *_buf, size_t n)
181{
182	u_char *buf = (u_char *)_buf;
183	u_char *keystream;
184	size_t m;
185
186	_rs_stir_if_needed(n);
187	while (n > 0) {
188		if (rs->rs_have > 0) {
189			m = arc4_min(n, rs->rs_have);
190			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
191			    - rs->rs_have;
192			memcpy(buf, keystream, m);
193			memset(keystream, 0, m);
194			buf += m;
195			n -= m;
196			rs->rs_have -= m;
197		}
198		if (rs->rs_have == 0)
199			_rs_rekey(NULL, 0);
200	}
201}
202
203static inline void
204_rs_random_u32(uint32_t *val)
205{
206	u_char *keystream;
207	_rs_stir_if_needed(sizeof(*val));
208	if (rs->rs_have < sizeof(*val))
209		_rs_rekey(NULL, 0);
210	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
211	memcpy(val, keystream, sizeof(*val));
212	memset(keystream, 0, sizeof(*val));
213	rs->rs_have -= sizeof(*val);
214}
215
216uint32_t
217arc4random(void)
218{
219	uint32_t val;
220
221	_ARC4_LOCK();
222	_rs_random_u32(&val);
223	_ARC4_UNLOCK();
224	return val;
225}
226
227void
228arc4random_buf(void *buf, size_t n)
229{
230	_ARC4_LOCK();
231	_rs_random_buf(buf, n);
232	_ARC4_UNLOCK();
233}
234