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 #include <sys/cdefs.h>
27 #include "namespace.h"
28 #if defined(__FreeBSD__)
29 #include <assert.h>
30 #endif
31 #include <fcntl.h>
32 #include <limits.h>
33 #include <pthread.h>
34 #include <signal.h>
35 #include <stdint.h>
36 #include <stdlib.h>
37 #include <string.h>
38 #include <unistd.h>
39 #include <sys/types.h>
40 #include <sys/time.h>
41
42 #include "libc_private.h"
43 #include "un-namespace.h"
44
45 #define CHACHA_EMBED
46 #define KEYSTREAM_ONLY
47 #if defined(__FreeBSD__)
48 #define ARC4RANDOM_FXRNG 1
49 #else
50 #define ARC4RANDOM_FXRNG 0
51 #endif
52 #include "chacha.c"
53
54 #define minimum(a, b) ((a) < (b) ? (a) : (b))
55
56 #if defined(__GNUC__) || defined(_MSC_VER)
57 #define inline __inline
58 #else /* __GNUC__ || _MSC_VER */
59 #define inline
60 #endif /* !__GNUC__ && !_MSC_VER */
61
62 #define KEYSZ 32
63 #define IVSZ 8
64 #define BLOCKSZ 64
65 #define RSBUFSZ (16*BLOCKSZ)
66
67 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */
68
69 /* Marked INHERIT_ZERO, so zero'd out in fork children. */
70 static struct _rs {
71 size_t rs_have; /* valid bytes at end of rs_buf */
72 size_t rs_count; /* bytes till reseed */
73 } *rs;
74
75 /* Maybe be preserved in fork children, if _rs_allocate() decides. */
76 static struct _rsx {
77 chacha_ctx rs_chacha; /* chacha context for random keystream */
78 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
79 #ifdef __FreeBSD__
80 uint32_t rs_seed_generation; /* 32-bit userspace RNG version */
81 #endif
82 } *rsx;
83
84 static inline int _rs_allocate(struct _rs **, struct _rsx **);
85 static inline void _rs_forkdetect(void);
86 #include "arc4random.h"
87
88 static inline void _rs_rekey(u_char *dat, size_t datlen);
89
90 static inline void
_rs_init(u_char * buf,size_t n)91 _rs_init(u_char *buf, size_t n)
92 {
93 if (n < KEYSZ + IVSZ)
94 return;
95
96 if (rs == NULL) {
97 if (_rs_allocate(&rs, &rsx) == -1)
98 _exit(1);
99 }
100
101 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
102 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ, NULL);
103 }
104
105 static void
_rs_stir(void)106 _rs_stir(void)
107 {
108 u_char rnd[KEYSZ + IVSZ];
109 uint32_t rekey_fuzz = 0;
110
111 #if defined(__FreeBSD__)
112 bool need_init;
113
114 /*
115 * De-couple allocation (which locates the vdso_fxrngp pointer in
116 * auxinfo) from initialization. This allows us to read the root seed
117 * version before we fetch system entropy, maintaining the invariant
118 * that the PRF was seeded with entropy from rs_seed_generation or a
119 * later generation. But never seeded from an earlier generation.
120 * This invariant prevents us from missing a root reseed event.
121 */
122 need_init = false;
123 if (rs == NULL) {
124 if (_rs_allocate(&rs, &rsx) == -1)
125 abort();
126 need_init = true;
127 }
128 /*
129 * Transition period: new userspace on old kernel. This should become
130 * a hard error at some point, if the scheme is adopted.
131 */
132 if (vdso_fxrngp != NULL)
133 rsx->rs_seed_generation =
134 fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32);
135 #endif
136
137 if (getentropy(rnd, sizeof rnd) == -1)
138 _getentropy_fail();
139
140 #if !defined(__FreeBSD__)
141 if (!rs)
142 _rs_init(rnd, sizeof(rnd));
143 #else /* __FreeBSD__ */
144 assert(rs != NULL);
145 if (need_init)
146 _rs_init(rnd, sizeof(rnd));
147 #endif
148 else
149 _rs_rekey(rnd, sizeof(rnd));
150 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
151
152 /* invalidate rs_buf */
153 rs->rs_have = 0;
154 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
155
156 /* rekey interval should not be predictable */
157 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
158 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
159 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
160 }
161
162 static inline void
_rs_stir_if_needed(size_t len)163 _rs_stir_if_needed(size_t len)
164 {
165 _rs_forkdetect();
166 if (!rs || rs->rs_count <= len)
167 _rs_stir();
168 if (rs->rs_count <= len)
169 rs->rs_count = 0;
170 else
171 rs->rs_count -= len;
172 }
173
174 static inline void
_rs_rekey(u_char * dat,size_t datlen)175 _rs_rekey(u_char *dat, size_t datlen)
176 {
177 #ifndef KEYSTREAM_ONLY
178 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
179 #endif
180 /* fill rs_buf with the keystream */
181 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
182 rsx->rs_buf, sizeof(rsx->rs_buf));
183 /* mix in optional user provided data */
184 if (dat) {
185 size_t i, m;
186
187 m = minimum(datlen, KEYSZ + IVSZ);
188 for (i = 0; i < m; i++)
189 rsx->rs_buf[i] ^= dat[i];
190 }
191 /* immediately reinit for backtracking resistance */
192 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
193 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
194 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
195 }
196
197 static inline void
_rs_random_buf(void * _buf,size_t n)198 _rs_random_buf(void *_buf, size_t n)
199 {
200 u_char *buf = (u_char *)_buf;
201 u_char *keystream;
202 size_t m;
203
204 _rs_stir_if_needed(n);
205 while (n > 0) {
206 if (rs->rs_have > 0) {
207 m = minimum(n, rs->rs_have);
208 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
209 - rs->rs_have;
210 memcpy(buf, keystream, m);
211 memset(keystream, 0, m);
212 buf += m;
213 n -= m;
214 rs->rs_have -= m;
215 }
216 if (rs->rs_have == 0)
217 _rs_rekey(NULL, 0);
218 }
219 }
220
221 static inline void
_rs_random_u32(uint32_t * val)222 _rs_random_u32(uint32_t *val)
223 {
224 u_char *keystream;
225
226 _rs_stir_if_needed(sizeof(*val));
227 if (rs->rs_have < sizeof(*val))
228 _rs_rekey(NULL, 0);
229 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
230 memcpy(val, keystream, sizeof(*val));
231 memset(keystream, 0, sizeof(*val));
232 rs->rs_have -= sizeof(*val);
233 }
234
235 uint32_t
arc4random(void)236 arc4random(void)
237 {
238 uint32_t val;
239
240 _ARC4_LOCK();
241 _rs_random_u32(&val);
242 _ARC4_UNLOCK();
243 return val;
244 }
245
246 void
arc4random_buf(void * buf,size_t n)247 arc4random_buf(void *buf, size_t n)
248 {
249 _ARC4_LOCK();
250 _rs_random_buf(buf, n);
251 _ARC4_UNLOCK();
252 }
253