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}