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 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 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 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 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 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 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 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 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 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 307 arc4random_buf(void *buf, size_t n) 308 { 309 _ARC4_LOCK(); 310 _rs_random_buf(buf, n); 311 _ARC4_UNLOCK(); 312 } 313