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 UB_ON_WINDOWS
39 #include <sys/mman.h>
40 #endif
41
42 #define KEYSTREAM_ONLY
43 #include "chacha_private.h"
44
45 #define arc4_min(a, b) ((a) < (b) ? (a) : (b))
46 #ifdef __GNUC__
47 #define inline __inline
48 #else /* !__GNUC__ */
49 #define inline
50 #endif /* !__GNUC__ */
51 #ifndef MAP_ANON
52 #define MAP_ANON MAP_ANONYMOUS
53 #endif
54
55 #define KEYSZ 32
56 #define IVSZ 8
57 #define BLOCKSZ 64
58 #define RSBUFSZ (16*BLOCKSZ)
59
60 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */
61
62 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
63 static struct {
64 size_t rs_have; /* valid bytes at end of rs_buf */
65 size_t rs_count; /* bytes till reseed */
66 } *rs;
67
68 /* Preserved in fork children. */
69 static struct {
70 chacha_ctx rs_chacha; /* chacha context for random keystream */
71 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
72 } *rsx;
73
74 static inline void _rs_rekey(u_char *dat, size_t datlen);
75
76 /*
77 * Basic sanity checking; wish we could do better.
78 */
79 static int
fallback_gotdata(char * buf,size_t len)80 fallback_gotdata(char *buf, size_t len)
81 {
82 char any_set = 0;
83 size_t i;
84
85 for (i = 0; i < len; ++i)
86 any_set |= buf[i];
87 if (any_set == 0)
88 return -1;
89 return 0;
90 }
91
92 /* fallback for getentropy in case libc returns failure */
93 static int
fallback_getentropy_urandom(void * buf,size_t len)94 fallback_getentropy_urandom(void *buf, size_t len)
95 {
96 size_t i;
97 int fd, flags;
98 int save_errno = errno;
99
100 start:
101
102 flags = O_RDONLY;
103 #ifdef O_NOFOLLOW
104 flags |= O_NOFOLLOW;
105 #endif
106 #ifdef O_CLOEXEC
107 flags |= O_CLOEXEC;
108 #endif
109 fd = open("/dev/urandom", flags, 0);
110 if (fd == -1) {
111 if (errno == EINTR)
112 goto start;
113 goto nodevrandom;
114 }
115 #ifndef O_CLOEXEC
116 # ifdef HAVE_FCNTL
117 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
118 # endif
119 #endif
120 for (i = 0; i < len; ) {
121 size_t wanted = len - i;
122 ssize_t ret = read(fd, (char*)buf + i, wanted);
123
124 if (ret == -1) {
125 if (errno == EAGAIN || errno == EINTR)
126 continue;
127 close(fd);
128 goto nodevrandom;
129 }
130 i += ret;
131 }
132 close(fd);
133 if (fallback_gotdata(buf, len) == 0) {
134 errno = save_errno;
135 return 0; /* satisfied */
136 }
137 nodevrandom:
138 errno = EIO;
139 return -1;
140 }
141
142 static inline void
_rs_init(u_char * buf,size_t n)143 _rs_init(u_char *buf, size_t n)
144 {
145 assert(buf);
146 if (n < KEYSZ + IVSZ)
147 return;
148
149 if (rs == NULL) {
150 #ifndef UB_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 UB_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 }
175
176 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
177 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
178 }
179
180 static void
_rs_stir(void)181 _rs_stir(void)
182 {
183 u_char rnd[KEYSZ + IVSZ];
184 uint32_t rekey_fuzz = 0;
185
186 if (getentropy(rnd, sizeof rnd) == -1) {
187 if(errno != ENOSYS ||
188 fallback_getentropy_urandom(rnd, sizeof rnd) == -1) {
189 #ifdef SIGKILL
190 raise(SIGKILL);
191 #else
192 exit(9); /* windows */
193 #endif
194 }
195 }
196
197 if (!rs)
198 _rs_init(rnd, sizeof(rnd));
199 else
200 _rs_rekey(rnd, sizeof(rnd));
201 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
202
203 /* invalidate rs_buf */
204 rs->rs_have = 0;
205 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
206
207 /* rekey interval should not be predictable */
208 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
209 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
210 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
211 }
212
213 static inline void
_rs_stir_if_needed(size_t len)214 _rs_stir_if_needed(size_t len)
215 {
216 #ifndef MAP_INHERIT_ZERO
217 static pid_t _rs_pid = 0;
218 pid_t pid = getpid();
219
220 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */
221 if (_rs_pid == 0 || _rs_pid != pid) {
222 _rs_pid = pid;
223 if (rs)
224 rs->rs_count = 0;
225 }
226 #endif
227 if (!rs || rs->rs_count <= len)
228 _rs_stir();
229 if (rs->rs_count <= len)
230 rs->rs_count = 0;
231 else
232 rs->rs_count -= len;
233 }
234
235 static inline void
_rs_rekey(u_char * dat,size_t datlen)236 _rs_rekey(u_char *dat, size_t datlen)
237 {
238 #ifndef KEYSTREAM_ONLY
239 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
240 #endif
241 /* fill rs_buf with the keystream */
242 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
243 rsx->rs_buf, sizeof(rsx->rs_buf));
244 /* mix in optional user provided data */
245 if (dat) {
246 size_t i, m;
247
248 m = arc4_min(datlen, KEYSZ + IVSZ);
249 for (i = 0; i < m; i++)
250 rsx->rs_buf[i] ^= dat[i];
251 }
252 /* immediately reinit for backtracking resistance */
253 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
254 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
255 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
256 }
257
258 static inline void
_rs_random_buf(void * _buf,size_t n)259 _rs_random_buf(void *_buf, size_t n)
260 {
261 u_char *buf = (u_char *)_buf;
262 u_char *keystream;
263 size_t m;
264
265 _rs_stir_if_needed(n);
266 while (n > 0) {
267 if (rs->rs_have > 0) {
268 m = arc4_min(n, rs->rs_have);
269 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
270 - rs->rs_have;
271 memcpy(buf, keystream, m);
272 memset(keystream, 0, m);
273 buf += m;
274 n -= m;
275 rs->rs_have -= m;
276 }
277 if (rs->rs_have == 0)
278 _rs_rekey(NULL, 0);
279 }
280 }
281
282 static inline void
_rs_random_u32(uint32_t * val)283 _rs_random_u32(uint32_t *val)
284 {
285 u_char *keystream;
286 _rs_stir_if_needed(sizeof(*val));
287 if (rs->rs_have < sizeof(*val))
288 _rs_rekey(NULL, 0);
289 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
290 memcpy(val, keystream, sizeof(*val));
291 memset(keystream, 0, sizeof(*val));
292 rs->rs_have -= sizeof(*val);
293 }
294
295 uint32_t
arc4random(void)296 arc4random(void)
297 {
298 uint32_t val;
299
300 _ARC4_LOCK();
301 _rs_random_u32(&val);
302 _ARC4_UNLOCK();
303 return val;
304 }
305
306 void
arc4random_buf(void * buf,size_t n)307 arc4random_buf(void *buf, size_t n)
308 {
309 _ARC4_LOCK();
310 _rs_random_buf(buf, n);
311 _ARC4_UNLOCK();
312 }
313