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 GETDNS_ON_WINDOWS
39 #include <sys/mman.h>
40 #endif
41 #if defined(GETDNS_ON_WINDOWS) && !defined(MAP_INHERIT_ZERO)
42 #define explicit_bzero(rnd, rnd_size) memset(rnd, 0, rnd_size)
43 #endif
44
45 #define KEYSTREAM_ONLY
46 #include "chacha_private.h"
47
48 #define arc4_min(a, b) ((a) < (b) ? (a) : (b))
49 #ifdef __GNUC__
50 #define inline __inline
51 #else /* !__GNUC__ */
52 #define inline
53 #endif /* !__GNUC__ */
54 #ifndef MAP_ANON
55 #define MAP_ANON MAP_ANONYMOUS
56 #endif
57
58 #define KEYSZ 32
59 #define IVSZ 8
60 #define BLOCKSZ 64
61 #define RSBUFSZ (16*BLOCKSZ)
62
63 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
64 static struct {
65 size_t rs_have; /* valid bytes at end of rs_buf */
66 size_t rs_count; /* bytes till reseed */
67 } *rs;
68
69 /* Preserved in fork children. */
70 static struct {
71 chacha_ctx rs_chacha; /* chacha context for random keystream */
72 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
73 } *rsx;
74
75 static inline void _rs_rekey(u_char *dat, size_t datlen);
76
77 /*
78 * Basic sanity checking; wish we could do better.
79 */
80 static int
fallback_gotdata(char * buf,size_t len)81 fallback_gotdata(char *buf, size_t len)
82 {
83 char any_set = 0;
84 size_t i;
85
86 for (i = 0; i < len; ++i)
87 any_set |= buf[i];
88 if (any_set == 0)
89 return -1;
90 return 0;
91 }
92
93 /* fallback for getentropy in case libc returns failure */
94 static int
fallback_getentropy_urandom(void * buf,size_t len)95 fallback_getentropy_urandom(void *buf, size_t len)
96 {
97 size_t i;
98 int fd, flags;
99 int save_errno = errno;
100
101 start:
102
103 flags = O_RDONLY;
104 #ifdef O_NOFOLLOW
105 flags |= O_NOFOLLOW;
106 #endif
107 #ifdef O_CLOEXEC
108 flags |= O_CLOEXEC;
109 #endif
110 fd = open("/dev/urandom", flags, 0);
111 if (fd == -1) {
112 if (errno == EINTR)
113 goto start;
114 goto nodevrandom;
115 }
116 #ifndef O_CLOEXEC
117 # ifdef HAVE_FCNTL
118 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
119 # endif
120 #endif
121 for (i = 0; i < len; ) {
122 size_t wanted = len - i;
123 ssize_t ret = read(fd, (char*)buf + i, wanted);
124
125 if (ret == -1) {
126 if (errno == EAGAIN || errno == EINTR)
127 continue;
128 close(fd);
129 goto nodevrandom;
130 }
131 i += ret;
132 }
133 close(fd);
134 if (fallback_gotdata(buf, len) == 0) {
135 errno = save_errno;
136 return 0; /* satisfied */
137 }
138 nodevrandom:
139 errno = EIO;
140 return -1;
141 }
142
143 static inline void
_rs_init(u_char * buf,size_t n)144 _rs_init(u_char *buf, size_t n)
145 {
146 if (n < KEYSZ + IVSZ)
147 return;
148
149 if (rs == NULL) {
150 #ifndef GETDNS_ON_WINDOWS
151 if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
152 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
153 abort();
154 #ifdef MAP_INHERIT_ZERO
155 if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1)
156 abort();
157 #endif
158 #else /* WINDOWS */
159 rs = malloc(sizeof(*rs));
160 if(!rs)
161 abort();
162 #endif
163 }
164 if (rsx == NULL) {
165 #ifndef GETDNS_ON_WINDOWS
166 if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE,
167 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
168 abort();
169 #else /* WINDOWS */
170 rsx = malloc(sizeof(*rsx));
171 if(!rsx)
172 abort();
173 #endif
174 /* Pleast older clang scan-build */
175 if (!buf)
176 buf = rsx->rs_buf;
177 }
178
179 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
180 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
181 }
182
183 static void
_rs_stir(void)184 _rs_stir(void)
185 {
186 u_char rnd[KEYSZ + IVSZ];
187
188 if (getentropy(rnd, sizeof rnd) == -1) {
189 if(errno != ENOSYS ||
190 fallback_getentropy_urandom(rnd, sizeof rnd) == -1) {
191 #ifdef SIGKILL
192 raise(SIGKILL);
193 #else
194 exit(9); /* windows */
195 #endif
196 }
197 }
198
199 if (!rs)
200 _rs_init(rnd, sizeof(rnd));
201 else
202 _rs_rekey(rnd, sizeof(rnd));
203 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
204
205 /* invalidate rs_buf */
206 rs->rs_have = 0;
207 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
208
209 rs->rs_count = 1600000;
210 }
211
212 static inline void
_rs_stir_if_needed(size_t len)213 _rs_stir_if_needed(size_t len)
214 {
215 #ifndef MAP_INHERIT_ZERO
216 static pid_t _rs_pid = 0;
217 pid_t pid = getpid();
218
219 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */
220 if (_rs_pid == 0 || _rs_pid != pid) {
221 _rs_pid = pid;
222 if (rs)
223 rs->rs_count = 0;
224 }
225 #endif
226 if (!rs || rs->rs_count <= len)
227 _rs_stir();
228 if (rs->rs_count <= len)
229 rs->rs_count = 0;
230 else
231 rs->rs_count -= len;
232 }
233
234 static inline void
_rs_rekey(u_char * dat,size_t datlen)235 _rs_rekey(u_char *dat, size_t datlen)
236 {
237 #ifndef KEYSTREAM_ONLY
238 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
239 #endif
240 /* fill rs_buf with the keystream */
241 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
242 rsx->rs_buf, sizeof(rsx->rs_buf));
243 /* mix in optional user provided data */
244 if (dat) {
245 size_t i, m;
246
247 m = arc4_min(datlen, KEYSZ + IVSZ);
248 for (i = 0; i < m; i++)
249 rsx->rs_buf[i] ^= dat[i];
250 }
251 /* immediately reinit for backtracking resistance */
252 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
253 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
254 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
255 }
256
257 static inline void
_rs_random_buf(void * _buf,size_t n)258 _rs_random_buf(void *_buf, size_t n)
259 {
260 u_char *buf = (u_char *)_buf;
261 u_char *keystream;
262 size_t m;
263
264 _rs_stir_if_needed(n);
265 while (n > 0) {
266 if (rs->rs_have > 0) {
267 m = arc4_min(n, rs->rs_have);
268 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
269 - rs->rs_have;
270 memcpy(buf, keystream, m);
271 memset(keystream, 0, m);
272 buf += m;
273 n -= m;
274 rs->rs_have -= m;
275 }
276 if (rs->rs_have == 0)
277 _rs_rekey(NULL, 0);
278 }
279 }
280
281 static inline void
_rs_random_u32(uint32_t * val)282 _rs_random_u32(uint32_t *val)
283 {
284 u_char *keystream;
285 _rs_stir_if_needed(sizeof(*val));
286 if (rs->rs_have < sizeof(*val))
287 _rs_rekey(NULL, 0);
288 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
289 memcpy(val, keystream, sizeof(*val));
290 memset(keystream, 0, sizeof(*val));
291 rs->rs_have -= sizeof(*val);
292 }
293
294 uint32_t
arc4random(void)295 arc4random(void)
296 {
297 uint32_t val;
298
299 _ARC4_LOCK();
300 _rs_random_u32(&val);
301 _ARC4_UNLOCK();
302 return val;
303 }
304
305 void
arc4random_buf(void * buf,size_t n)306 arc4random_buf(void *buf, size_t n)
307 {
308 _ARC4_LOCK();
309 _rs_random_buf(buf, n);
310 _ARC4_UNLOCK();
311 }
312