1 /* $OpenBSD: arc4random.c,v 1.44 2014/07/16 00:15:35 bcook 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 21 /* 22 * ChaCha based random number generator for OpenBSD. 23 */ 24 25 #include <fcntl.h> 26 #include <limits.h> 27 #include <signal.h> 28 #include <stdint.h> 29 #include <stdlib.h> 30 #include <string.h> 31 #include <unistd.h> 32 #include <sys/types.h> 33 #include <sys/param.h> 34 #include <sys/time.h> 35 #include <sys/mman.h> 36 37 #include "thread_private.h" 38 39 #define KEYSTREAM_ONLY 40 #include "chacha_private.h" 41 42 #define min(a, b) ((a) < (b) ? (a) : (b)) 43 #ifdef __GNUC__ 44 #define inline __inline 45 #else /* !__GNUC__ */ 46 #define inline 47 #endif /* !__GNUC__ */ 48 49 #define KEYSZ 32 50 #define IVSZ 8 51 #define BLOCKSZ 64 52 #define RSBUFSZ (16*BLOCKSZ) 53 54 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */ 55 static struct { 56 size_t rs_have; /* valid bytes at end of rs_buf */ 57 size_t rs_count; /* bytes till reseed */ 58 } *rs; 59 60 /* Preserved in fork children. */ 61 static struct { 62 chacha_ctx rs_chacha; /* chacha context for random keystream */ 63 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 64 } *rsx; 65 66 static inline void _rs_rekey(u_char *dat, size_t datlen); 67 68 static inline void 69 _rs_forkhandler(void) 70 { 71 if (rs) 72 rs->rs_count = 0; 73 } 74 75 static inline void 76 _rs_init(u_char *buf, size_t n) 77 { 78 if (n < KEYSZ + IVSZ) 79 return; 80 81 if (rs == NULL) { 82 if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE, 83 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 84 abort(); 85 #ifdef MAP_INHERIT_ZERO 86 if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1) 87 abort(); 88 #else 89 _ARC4_ATFORK(_rs_forkhandler); 90 #endif 91 } 92 if (rsx == NULL) { 93 if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE, 94 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 95 abort(); 96 } 97 98 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0); 99 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 100 } 101 102 static void 103 _rs_stir(void) 104 { 105 u_char rnd[KEYSZ + IVSZ]; 106 107 if (getentropy(rnd, sizeof rnd) == -1) 108 raise(SIGKILL); 109 110 if (!rs) 111 _rs_init(rnd, sizeof(rnd)); 112 else 113 _rs_rekey(rnd, sizeof(rnd)); 114 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 115 116 /* invalidate rs_buf */ 117 rs->rs_have = 0; 118 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 119 120 rs->rs_count = 1600000; 121 } 122 123 static inline void 124 _rs_stir_if_needed(size_t len) 125 { 126 #ifndef MAP_INHERIT_ZERO 127 static pid_t _rs_pid = 0; 128 pid_t pid = getpid(); 129 130 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */ 131 if (_rs_pid == 0 || _rs_pid != pid) { 132 _rs_pid = pid; 133 if (rs) 134 rs->rs_count = 0; 135 } 136 #endif 137 if (!rs || rs->rs_count <= len) 138 _rs_stir(); 139 if (rs->rs_count <= len) 140 rs->rs_count = 0; 141 else 142 rs->rs_count -= len; 143 } 144 145 static inline void 146 _rs_rekey(u_char *dat, size_t datlen) 147 { 148 #ifndef KEYSTREAM_ONLY 149 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 150 #endif 151 /* fill rs_buf with the keystream */ 152 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 153 rsx->rs_buf, sizeof(rsx->rs_buf)); 154 /* mix in optional user provided data */ 155 if (dat) { 156 size_t i, m; 157 158 m = min(datlen, KEYSZ + IVSZ); 159 for (i = 0; i < m; i++) 160 rsx->rs_buf[i] ^= dat[i]; 161 } 162 /* immediately reinit for backtracking resistance */ 163 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 164 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 165 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 166 } 167 168 static inline void 169 _rs_random_buf(void *_buf, size_t n) 170 { 171 u_char *buf = (u_char *)_buf; 172 u_char *keystream; 173 size_t m; 174 175 _rs_stir_if_needed(n); 176 while (n > 0) { 177 if (rs->rs_have > 0) { 178 m = min(n, rs->rs_have); 179 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 180 - rs->rs_have; 181 memcpy(buf, keystream, m); 182 memset(keystream, 0, m); 183 buf += m; 184 n -= m; 185 rs->rs_have -= m; 186 } 187 if (rs->rs_have == 0) 188 _rs_rekey(NULL, 0); 189 } 190 } 191 192 static inline void 193 _rs_random_u32(uint32_t *val) 194 { 195 u_char *keystream; 196 _rs_stir_if_needed(sizeof(*val)); 197 if (rs->rs_have < sizeof(*val)) 198 _rs_rekey(NULL, 0); 199 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 200 memcpy(val, keystream, sizeof(*val)); 201 memset(keystream, 0, sizeof(*val)); 202 rs->rs_have -= sizeof(*val); 203 } 204 205 uint32_t 206 arc4random(void) 207 { 208 uint32_t val; 209 210 _ARC4_LOCK(); 211 _rs_random_u32(&val); 212 _ARC4_UNLOCK(); 213 return val; 214 } 215 216 void 217 arc4random_buf(void *buf, size_t n) 218 { 219 _ARC4_LOCK(); 220 _rs_random_buf(buf, n); 221 _ARC4_UNLOCK(); 222 } 223