arc4random.c revision 285206 
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#include <stdint.h>
30#include <stdlib.h>
31#include <string.h>
32#include <unistd.h>
33#include <sys/types.h>
34#include <sys/param.h>
35#include <sys/time.h>
36#ifndef UB_ON_WINDOWS
37#include <sys/mman.h>
38#endif
39
40#define KEYSTREAM_ONLY
41#include "chacha_private.h"
42
43#define arc4_min(a, b) ((a) < (b) ? (a) : (b))
44#ifdef __GNUC__
45#define inline __inline
46#else				/* !__GNUC__ */
47#define inline
48#endif				/* !__GNUC__ */
49
50#define KEYSZ	32
51#define IVSZ	8
52#define BLOCKSZ	64
53#define RSBUFSZ	(16*BLOCKSZ)
54
55/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
56static struct {
57	size_t		rs_have;	/* valid bytes at end of rs_buf */
58	size_t		rs_count;	/* bytes till reseed */
59} *rs;
60
61/* Preserved in fork children. */
62static struct {
63	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
64	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
65} *rsx;
66
67static inline void _rs_rekey(u_char *dat, size_t datlen);
68
69static inline void
70_rs_init(u_char *buf, size_t n)
71{
72	if (n < KEYSZ + IVSZ)
73		return;
74
75	if (rs == NULL) {
76#ifndef UB_ON_WINDOWS
77		if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
78		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
79			abort();
80#ifdef MAP_INHERIT_ZERO
81		if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1)
82			abort();
83#endif
84#else /* WINDOWS */
85		rs = malloc(sizeof(*rs));
86		if(!rs)
87			abort();
88#endif
89	}
90	if (rsx == NULL) {
91#ifndef UB_ON_WINDOWS
92		if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE,
93		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
94			abort();
95#else /* WINDOWS */
96		rsx = malloc(sizeof(*rsx));
97		if(!rsx)
98			abort();
99#endif
100	}
101
102	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
103	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
104}
105
106static void
107_rs_stir(void)
108{
109	u_char rnd[KEYSZ + IVSZ];
110
111	if (getentropy(rnd, sizeof rnd) == -1) {
112#ifdef SIGKILL
113		raise(SIGKILL);
114#else
115		exit(9); /* windows */
116#endif
117	}
118
119	if (!rs)
120		_rs_init(rnd, sizeof(rnd));
121	else
122		_rs_rekey(rnd, sizeof(rnd));
123	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
124
125	/* invalidate rs_buf */
126	rs->rs_have = 0;
127	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
128
129	rs->rs_count = 1600000;
130}
131
132static inline void
133_rs_stir_if_needed(size_t len)
134{
135#ifndef MAP_INHERIT_ZERO
136	static pid_t _rs_pid = 0;
137	pid_t pid = getpid();
138
139	/* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */
140	if (_rs_pid == 0 || _rs_pid != pid) {
141		_rs_pid = pid;
142		if (rs)
143			rs->rs_count = 0;
144	}
145#endif
146	if (!rs || rs->rs_count <= len)
147		_rs_stir();
148	if (rs->rs_count <= len)
149		rs->rs_count = 0;
150	else
151		rs->rs_count -= len;
152}
153
154static inline void
155_rs_rekey(u_char *dat, size_t datlen)
156{
157#ifndef KEYSTREAM_ONLY
158	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
159#endif
160	/* fill rs_buf with the keystream */
161	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
162	    rsx->rs_buf, sizeof(rsx->rs_buf));
163	/* mix in optional user provided data */
164	if (dat) {
165		size_t i, m;
166
167		m = arc4_min(datlen, KEYSZ + IVSZ);
168		for (i = 0; i < m; i++)
169			rsx->rs_buf[i] ^= dat[i];
170	}
171	/* immediately reinit for backtracking resistance */
172	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
173	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
174	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
175}
176
177static inline void
178_rs_random_buf(void *_buf, size_t n)
179{
180	u_char *buf = (u_char *)_buf;
181	u_char *keystream;
182	size_t m;
183
184	_rs_stir_if_needed(n);
185	while (n > 0) {
186		if (rs->rs_have > 0) {
187			m = arc4_min(n, rs->rs_have);
188			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
189			    - rs->rs_have;
190			memcpy(buf, keystream, m);
191			memset(keystream, 0, m);
192			buf += m;
193			n -= m;
194			rs->rs_have -= m;
195		}
196		if (rs->rs_have == 0)
197			_rs_rekey(NULL, 0);
198	}
199}
200
201static inline void
202_rs_random_u32(uint32_t *val)
203{
204	u_char *keystream;
205	_rs_stir_if_needed(sizeof(*val));
206	if (rs->rs_have < sizeof(*val))
207		_rs_rekey(NULL, 0);
208	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
209	memcpy(val, keystream, sizeof(*val));
210	memset(keystream, 0, sizeof(*val));
211	rs->rs_have -= sizeof(*val);
212}
213
214uint32_t
215arc4random(void)
216{
217	uint32_t val;
218
219	_ARC4_LOCK();
220	_rs_random_u32(&val);
221	_ARC4_UNLOCK();
222	return val;
223}
224
225void
226arc4random_buf(void *buf, size_t n)
227{
228	_ARC4_LOCK();
229	_rs_random_buf(buf, n);
230	_ARC4_UNLOCK();
231}
232