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