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 "../config.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
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
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
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
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
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
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
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 
219 /*
220  * If we are providing arc4random, then we can provide a more efficient
221  * arc4random_buf().
222  */
223 # ifndef HAVE_ARC4RANDOM_BUF
224 void
225 arc4random_buf(void *buf, size_t n)
226 {
227 	_ARC4_LOCK();
228 	_rs_random_buf(buf, n);
229 	_ARC4_UNLOCK();
230 }
231 # endif /* !HAVE_ARC4RANDOM_BUF */
232 #endif /* !HAVE_ARC4RANDOM */
233 
234 /* arc4random_buf() that uses platform arc4random() */
235 #if !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM)
236 void
237 arc4random_buf(void *_buf, size_t n)
238 {
239 	size_t i;
240 	u_int32_t r = 0;
241 	char *buf = (char *)_buf;
242 
243 	for (i = 0; i < n; i++) {
244 		if (i % 4 == 0)
245 			r = arc4random();
246 		buf[i] = r & 0xff;
247 		r >>= 8;
248 	}
249 	explicit_bzero(&r, sizeof(r));
250 }
251 #endif /* !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM) */
252