1 /* $OpenBSD: arc4random.c,v 1.42 2014/07/12 18:57:41 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 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 #ifdef __OpenBSD__ 38 #include "thread_private.h" 39 #endif /* __OpenBSD__ */ 40 41 #define KEYSTREAM_ONLY 42 #include "chacha_private.h" 43 44 #define min(a, b) ((a) < (b) ? (a) : (b)) 45 #ifdef __GNUC__ 46 #define inline __inline 47 #else /* !__GNUC__ */ 48 #define inline 49 #endif /* !__GNUC__ */ 50 51 #define KEYSZ 32 52 #define IVSZ 8 53 #define BLOCKSZ 64 54 #define RSBUFSZ (16*BLOCKSZ) 55 56 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */ 57 static struct { 58 size_t rs_have; /* valid bytes at end of rs_buf */ 59 size_t rs_count; /* bytes till reseed */ 60 } *rs; 61 62 /* Preserved in fork children. */ 63 static struct { 64 chacha_ctx rs_chacha; /* chacha context for random keystream */ 65 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 66 } *rsx; 67 68 static inline void _rs_rekey(u_char *dat, size_t datlen); 69 70 static inline void 71 _rs_init(u_char *buf, size_t n) 72 { 73 if (n < KEYSZ + IVSZ) 74 return; 75 76 if (rs == NULL) { 77 if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE, 78 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 79 abort(); 80 #ifdef MAP_INHERIT_ZERO 81 if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1) 82 abort(); 83 #endif 84 } 85 if (rsx == NULL) { 86 if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE, 87 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 88 abort(); 89 } 90 91 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0); 92 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 93 } 94 95 static void 96 _rs_stir(void) 97 { 98 u_char rnd[KEYSZ + IVSZ]; 99 100 if (getentropy(rnd, sizeof rnd) == -1) 101 raise(SIGKILL); 102 103 if (!rs) 104 _rs_init(rnd, sizeof(rnd)); 105 else 106 _rs_rekey(rnd, sizeof(rnd)); 107 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 108 109 /* invalidate rs_buf */ 110 rs->rs_have = 0; 111 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 112 113 rs->rs_count = 1600000; 114 } 115 116 static inline void 117 _rs_stir_if_needed(size_t len) 118 { 119 #ifndef MAP_INHERIT_ZERO 120 static pid_t _rs_pid = 0; 121 pid_t pid = getpid(); 122 123 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */ 124 if (_rs_pid == 0 || _rs_pid != pid) { 125 _rs_pid = pid; 126 if (rs) 127 rs->rs_count = 0; 128 } 129 #endif 130 if (!rs || rs->rs_count <= len) 131 _rs_stir(); 132 if (rs->rs_count <= len) 133 rs->rs_count = 0; 134 else 135 rs->rs_count -= len; 136 } 137 138 static inline void 139 _rs_rekey(u_char *dat, size_t datlen) 140 { 141 #ifndef KEYSTREAM_ONLY 142 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 143 #endif 144 /* fill rs_buf with the keystream */ 145 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 146 rsx->rs_buf, sizeof(rsx->rs_buf)); 147 /* mix in optional user provided data */ 148 if (dat) { 149 size_t i, m; 150 151 m = min(datlen, KEYSZ + IVSZ); 152 for (i = 0; i < m; i++) 153 rsx->rs_buf[i] ^= dat[i]; 154 } 155 /* immediately reinit for backtracking resistance */ 156 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 157 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 158 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 159 } 160 161 static inline void 162 _rs_random_buf(void *_buf, size_t n) 163 { 164 u_char *buf = (u_char *)_buf; 165 u_char *keystream; 166 size_t m; 167 168 _rs_stir_if_needed(n); 169 while (n > 0) { 170 if (rs->rs_have > 0) { 171 m = min(n, rs->rs_have); 172 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 173 - rs->rs_have; 174 memcpy(buf, keystream, m); 175 memset(keystream, 0, m); 176 buf += m; 177 n -= m; 178 rs->rs_have -= m; 179 } 180 if (rs->rs_have == 0) 181 _rs_rekey(NULL, 0); 182 } 183 } 184 185 static inline void 186 _rs_random_u32(uint32_t *val) 187 { 188 u_char *keystream; 189 _rs_stir_if_needed(sizeof(*val)); 190 if (rs->rs_have < sizeof(*val)) 191 _rs_rekey(NULL, 0); 192 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 193 memcpy(val, keystream, sizeof(*val)); 194 memset(keystream, 0, sizeof(*val)); 195 rs->rs_have -= sizeof(*val); 196 } 197 198 uint32_t 199 arc4random(void) 200 { 201 uint32_t val; 202 203 _ARC4_LOCK(); 204 _rs_random_u32(&val); 205 _ARC4_UNLOCK(); 206 return val; 207 } 208 209 void 210 arc4random_buf(void *buf, size_t n) 211 { 212 _ARC4_LOCK(); 213 _rs_random_buf(buf, n); 214 _ARC4_UNLOCK(); 215 } 216