arc4random.c revision 307729 
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#ifndef MAP_ANON
52#define MAP_ANON MAP_ANONYMOUS
53#endif
54
55#define KEYSZ	32
56#define IVSZ	8
57#define BLOCKSZ	64
58#define RSBUFSZ	(16*BLOCKSZ)
59
60/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
61static struct {
62	size_t		rs_have;	/* valid bytes at end of rs_buf */
63	size_t		rs_count;	/* bytes till reseed */
64} *rs;
65
66/* Preserved in fork children. */
67static struct {
68	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
69	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
70} *rsx;
71
72static inline void _rs_rekey(u_char *dat, size_t datlen);
73
74static inline void
75_rs_init(u_char *buf, size_t n)
76{
77	if (n < KEYSZ + IVSZ)
78		return;
79
80	if (rs == NULL) {
81#ifndef UB_ON_WINDOWS
82		if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
83		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
84			abort();
85#ifdef MAP_INHERIT_ZERO
86		if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1)
87			abort();
88#endif
89#else /* WINDOWS */
90		rs = malloc(sizeof(*rs));
91		if(!rs)
92			abort();
93#endif
94	}
95	if (rsx == NULL) {
96#ifndef UB_ON_WINDOWS
97		if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE,
98		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
99			abort();
100#else /* WINDOWS */
101		rsx = malloc(sizeof(*rsx));
102		if(!rsx)
103			abort();
104#endif
105	}
106
107	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
108	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
109}
110
111static void
112_rs_stir(void)
113{
114	u_char rnd[KEYSZ + IVSZ];
115
116	if (getentropy(rnd, sizeof rnd) == -1) {
117#ifdef SIGKILL
118		raise(SIGKILL);
119#else
120		exit(9); /* windows */
121#endif
122	}
123
124	if (!rs)
125		_rs_init(rnd, sizeof(rnd));
126	else
127		_rs_rekey(rnd, sizeof(rnd));
128	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
129
130	/* invalidate rs_buf */
131	rs->rs_have = 0;
132	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
133
134	rs->rs_count = 1600000;
135}
136
137static inline void
138_rs_stir_if_needed(size_t len)
139{
140#ifndef MAP_INHERIT_ZERO
141	static pid_t _rs_pid = 0;
142	pid_t pid = getpid();
143
144	/* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */
145	if (_rs_pid == 0 || _rs_pid != pid) {
146		_rs_pid = pid;
147		if (rs)
148			rs->rs_count = 0;
149	}
150#endif
151	if (!rs || rs->rs_count <= len)
152		_rs_stir();
153	if (rs->rs_count <= len)
154		rs->rs_count = 0;
155	else
156		rs->rs_count -= len;
157}
158
159static inline void
160_rs_rekey(u_char *dat, size_t datlen)
161{
162#ifndef KEYSTREAM_ONLY
163	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
164#endif
165	/* fill rs_buf with the keystream */
166	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
167	    rsx->rs_buf, sizeof(rsx->rs_buf));
168	/* mix in optional user provided data */
169	if (dat) {
170		size_t i, m;
171
172		m = arc4_min(datlen, KEYSZ + IVSZ);
173		for (i = 0; i < m; i++)
174			rsx->rs_buf[i] ^= dat[i];
175	}
176	/* immediately reinit for backtracking resistance */
177	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
178	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
179	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
180}
181
182static inline void
183_rs_random_buf(void *_buf, size_t n)
184{
185	u_char *buf = (u_char *)_buf;
186	u_char *keystream;
187	size_t m;
188
189	_rs_stir_if_needed(n);
190	while (n > 0) {
191		if (rs->rs_have > 0) {
192			m = arc4_min(n, rs->rs_have);
193			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
194			    - rs->rs_have;
195			memcpy(buf, keystream, m);
196			memset(keystream, 0, m);
197			buf += m;
198			n -= m;
199			rs->rs_have -= m;
200		}
201		if (rs->rs_have == 0)
202			_rs_rekey(NULL, 0);
203	}
204}
205
206static inline void
207_rs_random_u32(uint32_t *val)
208{
209	u_char *keystream;
210	_rs_stir_if_needed(sizeof(*val));
211	if (rs->rs_have < sizeof(*val))
212		_rs_rekey(NULL, 0);
213	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
214	memcpy(val, keystream, sizeof(*val));
215	memset(keystream, 0, sizeof(*val));
216	rs->rs_have -= sizeof(*val);
217}
218
219uint32_t
220arc4random(void)
221{
222	uint32_t val;
223
224	_ARC4_LOCK();
225	_rs_random_u32(&val);
226	_ARC4_UNLOCK();
227	return val;
228}
229
230void
231arc4random_buf(void *buf, size_t n)
232{
233	_ARC4_LOCK();
234	_rs_random_buf(buf, n);
235	_ARC4_UNLOCK();
236}
237