1 /* $OpenBSD: arc4random.c,v 1.55 2019/03/24 17:56:54 deraadt Exp $ */
2
3 /*
4 * Copyright (c) 1996, David Mazieres <[email protected]>
5 * Copyright (c) 2008, Damien Miller <[email protected]>
6 * Copyright (c) 2013, Markus Friedl <[email protected]>
7 * Copyright (c) 2014, Theo de Raadt <[email protected]>
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 __FBSDID("$FreeBSD$");
28
29 #include "namespace.h"
30 #if defined(__FreeBSD__)
31 #include <assert.h>
32 #endif
33 #include <fcntl.h>
34 #include <limits.h>
35 #include <pthread.h>
36 #include <signal.h>
37 #include <stdint.h>
38 #include <stdlib.h>
39 #include <string.h>
40 #include <unistd.h>
41 #include <sys/types.h>
42 #include <sys/time.h>
43
44 #include "libc_private.h"
45 #include "un-namespace.h"
46
47 #define CHACHA_EMBED
48 #define KEYSTREAM_ONLY
49 #if defined(__FreeBSD__)
50 #define ARC4RANDOM_FXRNG 1
51 #else
52 #define ARC4RANDOM_FXRNG 0
53 #endif
54 #include "chacha.c"
55
56 #define minimum(a, b) ((a) < (b) ? (a) : (b))
57
58 #if defined(__GNUC__) || defined(_MSC_VER)
59 #define inline __inline
60 #else /* __GNUC__ || _MSC_VER */
61 #define inline
62 #endif /* !__GNUC__ && !_MSC_VER */
63
64 #define KEYSZ 32
65 #define IVSZ 8
66 #define BLOCKSZ 64
67 #define RSBUFSZ (16*BLOCKSZ)
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
110 #if defined(__FreeBSD__)
111 bool need_init;
112
113 /*
114 * De-couple allocation (which locates the vdso_fxrngp pointer in
115 * auxinfo) from initialization. This allows us to read the root seed
116 * version before we fetch system entropy, maintaining the invariant
117 * that the PRF was seeded with entropy from rs_seed_generation or a
118 * later generation. But never seeded from an earlier generation.
119 * This invariant prevents us from missing a root reseed event.
120 */
121 need_init = false;
122 if (rs == NULL) {
123 if (_rs_allocate(&rs, &rsx) == -1)
124 abort();
125 need_init = true;
126 }
127 /*
128 * Transition period: new userspace on old kernel. This should become
129 * a hard error at some point, if the scheme is adopted.
130 */
131 if (vdso_fxrngp != NULL)
132 rsx->rs_seed_generation =
133 fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32);
134 #endif
135
136 if (getentropy(rnd, sizeof rnd) == -1)
137 _getentropy_fail();
138
139 #if !defined(__FreeBSD__)
140 if (!rs)
141 _rs_init(rnd, sizeof(rnd));
142 #else /* __FreeBSD__ */
143 assert(rs != NULL);
144 if (need_init)
145 _rs_init(rnd, sizeof(rnd));
146 #endif
147 else
148 _rs_rekey(rnd, sizeof(rnd));
149 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
150
151 /* invalidate rs_buf */
152 rs->rs_have = 0;
153 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
154
155 rs->rs_count = 1600000;
156 }
157
158 static inline void
_rs_stir_if_needed(size_t len)159 _rs_stir_if_needed(size_t len)
160 {
161 _rs_forkdetect();
162 if (!rs || rs->rs_count <= len)
163 _rs_stir();
164 if (rs->rs_count <= len)
165 rs->rs_count = 0;
166 else
167 rs->rs_count -= len;
168 }
169
170 static inline void
_rs_rekey(u_char * dat,size_t datlen)171 _rs_rekey(u_char *dat, size_t datlen)
172 {
173 #ifndef KEYSTREAM_ONLY
174 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
175 #endif
176 /* fill rs_buf with the keystream */
177 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
178 rsx->rs_buf, sizeof(rsx->rs_buf));
179 /* mix in optional user provided data */
180 if (dat) {
181 size_t i, m;
182
183 m = minimum(datlen, KEYSZ + IVSZ);
184 for (i = 0; i < m; i++)
185 rsx->rs_buf[i] ^= dat[i];
186 }
187 /* immediately reinit for backtracking resistance */
188 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
189 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
190 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
191 }
192
193 static inline void
_rs_random_buf(void * _buf,size_t n)194 _rs_random_buf(void *_buf, size_t n)
195 {
196 u_char *buf = (u_char *)_buf;
197 u_char *keystream;
198 size_t m;
199
200 _rs_stir_if_needed(n);
201 while (n > 0) {
202 if (rs->rs_have > 0) {
203 m = minimum(n, rs->rs_have);
204 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
205 - rs->rs_have;
206 memcpy(buf, keystream, m);
207 memset(keystream, 0, m);
208 buf += m;
209 n -= m;
210 rs->rs_have -= m;
211 }
212 if (rs->rs_have == 0)
213 _rs_rekey(NULL, 0);
214 }
215 }
216
217 static inline void
_rs_random_u32(uint32_t * val)218 _rs_random_u32(uint32_t *val)
219 {
220 u_char *keystream;
221
222 _rs_stir_if_needed(sizeof(*val));
223 if (rs->rs_have < sizeof(*val))
224 _rs_rekey(NULL, 0);
225 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
226 memcpy(val, keystream, sizeof(*val));
227 memset(keystream, 0, sizeof(*val));
228 rs->rs_have -= sizeof(*val);
229 }
230
231 uint32_t
arc4random(void)232 arc4random(void)
233 {
234 uint32_t val;
235
236 _ARC4_LOCK();
237 _rs_random_u32(&val);
238 _ARC4_UNLOCK();
239 return val;
240 }
241
242 void
arc4random_buf(void * buf,size_t n)243 arc4random_buf(void *buf, size_t n)
244 {
245 _ARC4_LOCK();
246 _rs_random_buf(buf, n);
247 _ARC4_UNLOCK();
248 }
249