1 /* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb 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 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
8 *
9 * Permission to use, copy, modify, and distribute this software for any
10 * purpose with or without fee is hereby granted, provided that the above
11 * copyright notice and this permission notice appear in all copies.
12 *
13 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
14 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
15 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
16 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
17 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
18 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
19 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
20 */
21
22 /*
23 * ChaCha based random number generator for OpenBSD.
24 */
25
26 /* OPENBSD ORIGINAL: lib/libc/crypt/arc4random.c */
27
28 #include "includes.h"
29
30 #include <sys/types.h>
31
32 #include <fcntl.h>
33 #include <limits.h>
34 #include <signal.h>
35 #ifdef HAVE_STDINT_H
36 #include <stdint.h>
37 #endif
38 #include <stdlib.h>
39 #include <string.h>
40 #include <unistd.h>
41 #include <sys/types.h>
42 #include <sys/time.h>
43
44 #ifndef HAVE_ARC4RANDOM
45
46 /*
47 * Always use the getentropy implementation from bsd-getentropy.c, which
48 * will call a native getentropy if available then fall back as required.
49 * We use a different name so that OpenSSL cannot call the wrong getentropy.
50 */
51 int _ssh_compat_getentropy(void *, size_t);
52 #ifdef getentropy
53 # undef getentropy
54 #endif
55 #define getentropy(x, y) (_ssh_compat_getentropy((x), (y)))
56
57 #include "log.h"
58
59 #define KEYSTREAM_ONLY
60 #include "chacha_private.h"
61
62 #define minimum(a, b) ((a) < (b) ? (a) : (b))
63
64 #if defined(__GNUC__) || defined(_MSC_VER)
65 #define inline __inline
66 #else /* __GNUC__ || _MSC_VER */
67 #define inline
68 #endif /* !__GNUC__ && !_MSC_VER */
69
70 #define KEYSZ 32
71 #define IVSZ 8
72 #define BLOCKSZ 64
73 #define RSBUFSZ (16*BLOCKSZ)
74
75 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */
76
77 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
78 static struct _rs {
79 size_t rs_have; /* valid bytes at end of rs_buf */
80 size_t rs_count; /* bytes till reseed */
81 } *rs;
82
83 /* Maybe be preserved in fork children, if _rs_allocate() decides. */
84 static struct _rsx {
85 chacha_ctx rs_chacha; /* chacha context for random keystream */
86 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
87 } *rsx;
88
89 static inline int _rs_allocate(struct _rs **, struct _rsx **);
90 static inline void _rs_forkdetect(void);
91 #include "arc4random.h"
92
93 static inline void _rs_rekey(u_char *dat, size_t datlen);
94
95 static inline void
_rs_init(u_char * buf,size_t n)96 _rs_init(u_char *buf, size_t n)
97 {
98 if (n < KEYSZ + IVSZ)
99 return;
100
101 if (rs == NULL) {
102 if (_rs_allocate(&rs, &rsx) == -1)
103 _exit(1);
104 }
105
106 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
107 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
108 }
109
110 static void
_rs_stir(void)111 _rs_stir(void)
112 {
113 u_char rnd[KEYSZ + IVSZ];
114 uint32_t rekey_fuzz = 0;
115
116 if (getentropy(rnd, sizeof rnd) == -1)
117 _getentropy_fail();
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 /* rekey interval should not be predictable */
130 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
131 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
132 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
133 }
134
135 static inline void
_rs_stir_if_needed(size_t len)136 _rs_stir_if_needed(size_t len)
137 {
138 _rs_forkdetect();
139 if (!rs || rs->rs_count <= len)
140 _rs_stir();
141 if (rs->rs_count <= len)
142 rs->rs_count = 0;
143 else
144 rs->rs_count -= len;
145 }
146
147 static inline void
_rs_rekey(u_char * dat,size_t datlen)148 _rs_rekey(u_char *dat, size_t datlen)
149 {
150 #ifndef KEYSTREAM_ONLY
151 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
152 #endif
153 /* fill rs_buf with the keystream */
154 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
155 rsx->rs_buf, sizeof(rsx->rs_buf));
156 /* mix in optional user provided data */
157 if (dat) {
158 size_t i, m;
159
160 m = minimum(datlen, KEYSZ + IVSZ);
161 for (i = 0; i < m; i++)
162 rsx->rs_buf[i] ^= dat[i];
163 }
164 /* immediately reinit for backtracking resistance */
165 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
166 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
167 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
168 }
169
170 static inline void
_rs_random_buf(void * _buf,size_t n)171 _rs_random_buf(void *_buf, size_t n)
172 {
173 u_char *buf = (u_char *)_buf;
174 u_char *keystream;
175 size_t m;
176
177 _rs_stir_if_needed(n);
178 while (n > 0) {
179 if (rs->rs_have > 0) {
180 m = minimum(n, rs->rs_have);
181 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
182 - rs->rs_have;
183 memcpy(buf, keystream, m);
184 memset(keystream, 0, m);
185 buf += m;
186 n -= m;
187 rs->rs_have -= m;
188 }
189 if (rs->rs_have == 0)
190 _rs_rekey(NULL, 0);
191 }
192 }
193
194 static inline void
_rs_random_u32(uint32_t * val)195 _rs_random_u32(uint32_t *val)
196 {
197 u_char *keystream;
198
199 _rs_stir_if_needed(sizeof(*val));
200 if (rs->rs_have < sizeof(*val))
201 _rs_rekey(NULL, 0);
202 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
203 memcpy(val, keystream, sizeof(*val));
204 memset(keystream, 0, sizeof(*val));
205 rs->rs_have -= sizeof(*val);
206 }
207
208 uint32_t
arc4random(void)209 arc4random(void)
210 {
211 uint32_t val;
212
213 _ARC4_LOCK();
214 _rs_random_u32(&val);
215 _ARC4_UNLOCK();
216 return val;
217 }
218 DEF_WEAK(arc4random);
219
220 /*
221 * If we are providing arc4random, then we can provide a more efficient
222 * arc4random_buf().
223 */
224 # ifndef HAVE_ARC4RANDOM_BUF
225 void
arc4random_buf(void * buf,size_t n)226 arc4random_buf(void *buf, size_t n)
227 {
228 _ARC4_LOCK();
229 _rs_random_buf(buf, n);
230 _ARC4_UNLOCK();
231 }
232 DEF_WEAK(arc4random_buf);
233 # endif /* !HAVE_ARC4RANDOM_BUF */
234 #endif /* !HAVE_ARC4RANDOM */
235
236 /* arc4random_buf() that uses platform arc4random() */
237 #if !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM)
238 void
arc4random_buf(void * _buf,size_t n)239 arc4random_buf(void *_buf, size_t n)
240 {
241 size_t i;
242 u_int32_t r = 0;
243 char *buf = (char *)_buf;
244
245 for (i = 0; i < n; i++) {
246 if (i % 4 == 0)
247 r = arc4random();
248 buf[i] = r & 0xff;
249 r >>= 8;
250 }
251 explicit_bzero(&r, sizeof(r));
252 }
253 #endif /* !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM) */
254
255