arc4random.c revision 285206
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#include <stdint.h> 30#include <stdlib.h> 31#include <string.h> 32#include <unistd.h> 33#include <sys/types.h> 34#include <sys/param.h> 35#include <sys/time.h> 36#ifndef UB_ON_WINDOWS 37#include <sys/mman.h> 38#endif 39 40#define KEYSTREAM_ONLY 41#include "chacha_private.h" 42 43#define arc4_min(a, b) ((a) < (b) ? (a) : (b)) 44#ifdef __GNUC__ 45#define inline __inline 46#else /* !__GNUC__ */ 47#define inline 48#endif /* !__GNUC__ */ 49 50#define KEYSZ 32 51#define IVSZ 8 52#define BLOCKSZ 64 53#define RSBUFSZ (16*BLOCKSZ) 54 55/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */ 56static struct { 57 size_t rs_have; /* valid bytes at end of rs_buf */ 58 size_t rs_count; /* bytes till reseed */ 59} *rs; 60 61/* Preserved in fork children. */ 62static struct { 63 chacha_ctx rs_chacha; /* chacha context for random keystream */ 64 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 65} *rsx; 66 67static inline void _rs_rekey(u_char *dat, size_t datlen); 68 69static inline void 70_rs_init(u_char *buf, size_t n) 71{ 72 if (n < KEYSZ + IVSZ) 73 return; 74 75 if (rs == NULL) { 76#ifndef UB_ON_WINDOWS 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#else /* WINDOWS */ 85 rs = malloc(sizeof(*rs)); 86 if(!rs) 87 abort(); 88#endif 89 } 90 if (rsx == NULL) { 91#ifndef UB_ON_WINDOWS 92 if ((rsx = mmap(NULL, sizeof(*rsx), PROT_READ|PROT_WRITE, 93 MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED) 94 abort(); 95#else /* WINDOWS */ 96 rsx = malloc(sizeof(*rsx)); 97 if(!rsx) 98 abort(); 99#endif 100 } 101 102 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0); 103 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 104} 105 106static void 107_rs_stir(void) 108{ 109 u_char rnd[KEYSZ + IVSZ]; 110 111 if (getentropy(rnd, sizeof rnd) == -1) { 112#ifdef SIGKILL 113 raise(SIGKILL); 114#else 115 exit(9); /* windows */ 116#endif 117 } 118 119 if (!rs) 120 _rs_init(rnd, sizeof(rnd)); 121 else 122 _rs_rekey(rnd, sizeof(rnd)); 123 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 124 125 /* invalidate rs_buf */ 126 rs->rs_have = 0; 127 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 128 129 rs->rs_count = 1600000; 130} 131 132static inline void 133_rs_stir_if_needed(size_t len) 134{ 135#ifndef MAP_INHERIT_ZERO 136 static pid_t _rs_pid = 0; 137 pid_t pid = getpid(); 138 139 /* If a system lacks MAP_INHERIT_ZERO, resort to getpid() */ 140 if (_rs_pid == 0 || _rs_pid != pid) { 141 _rs_pid = pid; 142 if (rs) 143 rs->rs_count = 0; 144 } 145#endif 146 if (!rs || rs->rs_count <= len) 147 _rs_stir(); 148 if (rs->rs_count <= len) 149 rs->rs_count = 0; 150 else 151 rs->rs_count -= len; 152} 153 154static inline void 155_rs_rekey(u_char *dat, size_t datlen) 156{ 157#ifndef KEYSTREAM_ONLY 158 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 159#endif 160 /* fill rs_buf with the keystream */ 161 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 162 rsx->rs_buf, sizeof(rsx->rs_buf)); 163 /* mix in optional user provided data */ 164 if (dat) { 165 size_t i, m; 166 167 m = arc4_min(datlen, KEYSZ + IVSZ); 168 for (i = 0; i < m; i++) 169 rsx->rs_buf[i] ^= dat[i]; 170 } 171 /* immediately reinit for backtracking resistance */ 172 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 173 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 174 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 175} 176 177static inline void 178_rs_random_buf(void *_buf, size_t n) 179{ 180 u_char *buf = (u_char *)_buf; 181 u_char *keystream; 182 size_t m; 183 184 _rs_stir_if_needed(n); 185 while (n > 0) { 186 if (rs->rs_have > 0) { 187 m = arc4_min(n, rs->rs_have); 188 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 189 - rs->rs_have; 190 memcpy(buf, keystream, m); 191 memset(keystream, 0, m); 192 buf += m; 193 n -= m; 194 rs->rs_have -= m; 195 } 196 if (rs->rs_have == 0) 197 _rs_rekey(NULL, 0); 198 } 199} 200 201static inline void 202_rs_random_u32(uint32_t *val) 203{ 204 u_char *keystream; 205 _rs_stir_if_needed(sizeof(*val)); 206 if (rs->rs_have < sizeof(*val)) 207 _rs_rekey(NULL, 0); 208 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 209 memcpy(val, keystream, sizeof(*val)); 210 memset(keystream, 0, sizeof(*val)); 211 rs->rs_have -= sizeof(*val); 212} 213 214uint32_t 215arc4random(void) 216{ 217 uint32_t val; 218 219 _ARC4_LOCK(); 220 _rs_random_u32(&val); 221 _ARC4_UNLOCK(); 222 return val; 223} 224 225void 226arc4random_buf(void *buf, size_t n) 227{ 228 _ARC4_LOCK(); 229 _rs_random_buf(buf, n); 230 _ARC4_UNLOCK(); 231} 232