1 /* $OpenBSD: arc4random.c,v 1.54 2015/09/13 08:31:47 guenther 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 <fcntl.h> 27 #include <limits.h> 28 #include <signal.h> 29 #include <stdint.h> 30 #include <stdlib.h> 31 #include <string.h> 32 #include <unistd.h> 33 #include <sys/types.h> 34 #include <sys/time.h> 35 36 #define KEYSTREAM_ONLY 37 #include "chacha_private.h" 38 39 #define minimum(a, b) ((a) < (b) ? (a) : (b)) 40 41 #if defined(__GNUC__) || defined(_MSC_VER) 42 #define inline __inline 43 #else /* __GNUC__ || _MSC_VER */ 44 #define inline 45 #endif /* !__GNUC__ && !_MSC_VER */ 46 47 #define KEYSZ 32 48 #define IVSZ 8 49 #define BLOCKSZ 64 50 #define RSBUFSZ (16*BLOCKSZ) 51 52 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */ 53 static struct _rs { 54 size_t rs_have; /* valid bytes at end of rs_buf */ 55 size_t rs_count; /* bytes till reseed */ 56 } *rs; 57 58 /* Maybe be preserved in fork children, if _rs_allocate() decides. */ 59 static struct _rsx { 60 chacha_ctx rs_chacha; /* chacha context for random keystream */ 61 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 62 } *rsx; 63 64 65 /* 66 * Stub functions for portability. 67 */ 68 69 #include <sys/mman.h> 70 71 #include <pthread.h> 72 #include <signal.h> 73 74 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER; 75 #define _ARC4_LOCK() pthread_mutex_lock(&arc4random_mtx) 76 #define _ARC4_UNLOCK() pthread_mutex_unlock(&arc4random_mtx) 77 78 #ifdef __GLIBC__ 79 extern void *__dso_handle; 80 extern int __register_atfork(void (*)(void), void(*)(void), void (*)(void), void *); 81 #define _ARC4_ATFORK(f) __register_atfork(NULL, NULL, (f), __dso_handle) 82 #else 83 /* 84 * Unfortunately, pthread_atfork() is broken on FreeBSD (at least 9 and 10) if 85 * a program does not link to -lthr. Callbacks registered with pthread_atfork() 86 * appear to fail silently. So, it is not always possible to detect a PID 87 * wraparound. 88 */ 89 #define _ARC4_ATFORK(f) pthread_atfork(NULL, NULL, (f)) 90 #endif 91 92 static inline void 93 _getentropy_fail(void) 94 { 95 raise(SIGKILL); 96 } 97 98 static volatile sig_atomic_t _rs_forked; 99 100 static inline void 101 _rs_forkhandler(void) 102 { 103 _rs_forked = 1; 104 } 105 106 static inline void 107 _rs_forkdetect(void) 108 { 109 static pid_t _rs_pid = 0; 110 pid_t pid = getpid(); 111 112 if (_rs_pid == 0 || _rs_pid != pid || _rs_forked) { 113 _rs_pid = pid; 114 _rs_forked = 0; 115 if (rs) 116 memset(rs, 0, sizeof(*rs)); 117 } 118 } 119 120 static inline int 121 _rs_allocate(struct _rs **rsp, struct _rsx **rsxp) 122 { 123 if ((*rsp = mmap(NULL, sizeof(**rsp), PROT_READ|PROT_WRITE, 124 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 125 return (-1); 126 127 if ((*rsxp = mmap(NULL, sizeof(**rsxp), PROT_READ|PROT_WRITE, 128 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) { 129 munmap(*rsp, sizeof(**rsp)); 130 return (-1); 131 } 132 133 _ARC4_ATFORK(_rs_forkhandler); 134 return (0); 135 } 136 137 static inline void _rs_rekey(u_char *dat, size_t datlen); 138 139 static inline void 140 _rs_init(u_char *buf, size_t n) 141 { 142 if (n < KEYSZ + IVSZ) 143 return; 144 145 if (rs == NULL) { 146 if (_rs_allocate(&rs, &rsx) == -1) 147 abort(); 148 } 149 150 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0); 151 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 152 } 153 154 static void 155 _rs_stir(void) 156 { 157 u_char rnd[KEYSZ + IVSZ]; 158 159 if (getentropy(rnd, sizeof rnd) == -1) 160 _getentropy_fail(); 161 162 if (!rs) 163 _rs_init(rnd, sizeof(rnd)); 164 else 165 _rs_rekey(rnd, sizeof(rnd)); 166 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 167 168 /* invalidate rs_buf */ 169 rs->rs_have = 0; 170 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 171 172 rs->rs_count = 1600000; 173 } 174 175 static inline void 176 _rs_stir_if_needed(size_t len) 177 { 178 _rs_forkdetect(); 179 if (!rs || rs->rs_count <= len) 180 _rs_stir(); 181 if (rs->rs_count <= len) 182 rs->rs_count = 0; 183 else 184 rs->rs_count -= len; 185 } 186 187 static inline void 188 _rs_rekey(u_char *dat, size_t datlen) 189 { 190 #ifndef KEYSTREAM_ONLY 191 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 192 #endif 193 /* fill rs_buf with the keystream */ 194 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 195 rsx->rs_buf, sizeof(rsx->rs_buf)); 196 /* mix in optional user provided data */ 197 if (dat) { 198 size_t i, m; 199 200 m = minimum(datlen, KEYSZ + IVSZ); 201 for (i = 0; i < m; i++) 202 rsx->rs_buf[i] ^= dat[i]; 203 } 204 /* immediately reinit for backtracking resistance */ 205 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 206 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 207 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 208 } 209 210 static inline void 211 _rs_random_buf(void *_buf, size_t n) 212 { 213 u_char *buf = (u_char *)_buf; 214 u_char *keystream; 215 size_t m; 216 217 _rs_stir_if_needed(n); 218 while (n > 0) { 219 if (rs->rs_have > 0) { 220 m = minimum(n, rs->rs_have); 221 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 222 - rs->rs_have; 223 memcpy(buf, keystream, m); 224 memset(keystream, 0, m); 225 buf += m; 226 n -= m; 227 rs->rs_have -= m; 228 } 229 if (rs->rs_have == 0) 230 _rs_rekey(NULL, 0); 231 } 232 } 233 234 static inline void 235 _rs_random_u32(uint32_t *val) 236 { 237 u_char *keystream; 238 239 _rs_stir_if_needed(sizeof(*val)); 240 if (rs->rs_have < sizeof(*val)) 241 _rs_rekey(NULL, 0); 242 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 243 memcpy(val, keystream, sizeof(*val)); 244 memset(keystream, 0, sizeof(*val)); 245 rs->rs_have -= sizeof(*val); 246 } 247 248 uint32_t 249 arc4random(void) 250 { 251 uint32_t val; 252 253 _ARC4_LOCK(); 254 _rs_random_u32(&val); 255 _ARC4_UNLOCK(); 256 return val; 257 } 258 259 void 260 arc4random_buf(void *buf, size_t n) 261 { 262 _ARC4_LOCK(); 263 _rs_random_buf(buf, n); 264 _ARC4_UNLOCK(); 265 } 266