1 /* $OpenBSD: arc4random.c,v 1.43 2014/07/13 09:32:42 beck 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_init(u_char *buf, size_t n) 70 { 71 if (n < KEYSZ + IVSZ) 72 return; 73 74 if (rs == NULL) { 75 if ((rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE, 76 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 77 abort(); 78 #ifdef MAP_INHERIT_ZERO 79 if (minherit(rs, sizeof(*rs), MAP_INHERIT_ZERO) == -1) 80 abort(); 81 #endif 82 } 83 if (rsx == NULL) { 84 if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE, 85 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 86 abort(); 87 } 88 89 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0); 90 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 91 } 92 93 static void 94 _rs_stir(void) 95 { 96 u_char rnd[KEYSZ + IVSZ]; 97 98 if (getentropy(rnd, sizeof rnd) == -1) 99 raise(SIGKILL); 100 101 if (!rs) 102 _rs_init(rnd, sizeof(rnd)); 103 else 104 _rs_rekey(rnd, sizeof(rnd)); 105 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 106 107 /* invalidate rs_buf */ 108 rs->rs_have = 0; 109 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 110 111 rs->rs_count = 1600000; 112 } 113 114 static inline void 115 _rs_stir_if_needed(size_t len) 116 { 117 #ifndef MAP_INHERIT_ZERO 118 static pid_t _rs_pid = 0; 119 pid_t pid = getpid(); 120 121 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */ 122 if (_rs_pid == 0 || _rs_pid != pid) { 123 _rs_pid = pid; 124 if (rs) 125 rs->rs_count = 0; 126 } 127 #endif 128 if (!rs || rs->rs_count <= len) 129 _rs_stir(); 130 if (rs->rs_count <= len) 131 rs->rs_count = 0; 132 else 133 rs->rs_count -= len; 134 } 135 136 static inline void 137 _rs_rekey(u_char *dat, size_t datlen) 138 { 139 #ifndef KEYSTREAM_ONLY 140 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 141 #endif 142 /* fill rs_buf with the keystream */ 143 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 144 rsx->rs_buf, sizeof(rsx->rs_buf)); 145 /* mix in optional user provided data */ 146 if (dat) { 147 size_t i, m; 148 149 m = min(datlen, KEYSZ + IVSZ); 150 for (i = 0; i < m; i++) 151 rsx->rs_buf[i] ^= dat[i]; 152 } 153 /* immediately reinit for backtracking resistance */ 154 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 155 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 156 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 157 } 158 159 static inline void 160 _rs_random_buf(void *_buf, size_t n) 161 { 162 u_char *buf = (u_char *)_buf; 163 u_char *keystream; 164 size_t m; 165 166 _rs_stir_if_needed(n); 167 while (n > 0) { 168 if (rs->rs_have > 0) { 169 m = min(n, rs->rs_have); 170 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 171 - rs->rs_have; 172 memcpy(buf, keystream, m); 173 memset(keystream, 0, m); 174 buf += m; 175 n -= m; 176 rs->rs_have -= m; 177 } 178 if (rs->rs_have == 0) 179 _rs_rekey(NULL, 0); 180 } 181 } 182 183 static inline void 184 _rs_random_u32(uint32_t *val) 185 { 186 u_char *keystream; 187 _rs_stir_if_needed(sizeof(*val)); 188 if (rs->rs_have < sizeof(*val)) 189 _rs_rekey(NULL, 0); 190 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 191 memcpy(val, keystream, sizeof(*val)); 192 memset(keystream, 0, sizeof(*val)); 193 rs->rs_have -= sizeof(*val); 194 } 195 196 uint32_t 197 arc4random(void) 198 { 199 uint32_t val; 200 201 _ARC4_LOCK(); 202 _rs_random_u32(&val); 203 _ARC4_UNLOCK(); 204 return val; 205 } 206 207 void 208 arc4random_buf(void *buf, size_t n) 209 { 210 _ARC4_LOCK(); 211 _rs_random_buf(buf, n); 212 _ARC4_UNLOCK(); 213 } 214