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. */
58 static 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. */
64 static struct {
65 chacha_ctx rs_chacha; /* chacha context for random keystream */
66 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
67 } *rsx;
68
69 static inline void _rs_rekey(u_char *dat, size_t datlen);
70
71 static inline void
_rs_init(u_char * buf,size_t n)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
108 static void
_rs_stir(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
134 static inline void
_rs_stir_if_needed(size_t len)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
156 static inline void
_rs_rekey(u_char * dat,size_t datlen)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
179 static inline void
_rs_random_buf(void * _buf,size_t n)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
203 static inline void
_rs_random_u32(uint32_t * val)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
216 uint32_t
arc4random(void)217 arc4random(void)
218 {
219 uint32_t val;
220
221 _ARC4_LOCK();
222 _rs_random_u32(&val);
223 _ARC4_UNLOCK();
224 return val;
225 }
226
227 void
arc4random_buf(void * buf,size_t n)228 arc4random_buf(void *buf, size_t n)
229 {
230 _ARC4_LOCK();
231 _rs_random_buf(buf, n);
232 _ARC4_UNLOCK();
233 }
234