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On older kernels, when userspace program disables SIGSYS, catch ENOSYS and emulate getrandom(2) syscall with the kern.arandom sysctl (via existing arc4_sysctl wrapper). Special care is taken to faithfully emulate EFAULT on NULL pointers, because sysctl(3) as used by kern.arandom ignores NULL oldp. (This was caught by getentropy(3) ATF tests.) Reported by: kib Reviewed by: kib Discussed with: delphij Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D14785
301 lines
6.1 KiB
C
301 lines
6.1 KiB
C
/* $OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $ */
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/*
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* Copyright (c) 1996, David Mazieres <dm@uun.org>
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* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* Arc4 random number generator for OpenBSD.
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*
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* This code is derived from section 17.1 of Applied Cryptography,
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* second edition, which describes a stream cipher allegedly
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* compatible with RSA Labs "RC4" cipher (the actual description of
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* which is a trade secret). The same algorithm is used as a stream
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* cipher called "arcfour" in Tatu Ylonen's ssh package.
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*
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* RC4 is a registered trademark of RSA Laboratories.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "namespace.h"
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#include <fcntl.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include <sys/sysctl.h>
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#include <sys/time.h>
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#include <pthread.h>
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#include "libc_private.h"
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#include "un-namespace.h"
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#ifdef __GNUC__
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#define inline __inline
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#else /* !__GNUC__ */
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#define inline
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#endif /* !__GNUC__ */
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struct arc4_stream {
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u_int8_t i;
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u_int8_t j;
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u_int8_t s[256];
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};
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static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
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#define KEYSIZE 128
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#define _ARC4_LOCK() \
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do { \
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if (__isthreaded) \
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_pthread_mutex_lock(&arc4random_mtx); \
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} while (0)
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#define _ARC4_UNLOCK() \
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do { \
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if (__isthreaded) \
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_pthread_mutex_unlock(&arc4random_mtx); \
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} while (0)
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static int rs_initialized;
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static struct arc4_stream rs;
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static pid_t arc4_stir_pid;
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static int arc4_count;
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extern int __sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp,
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void *newp, size_t newlen);
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static inline u_int8_t arc4_getbyte(void);
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static void arc4_stir(void);
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static inline void
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arc4_init(void)
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{
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int n;
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for (n = 0; n < 256; n++)
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rs.s[n] = n;
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rs.i = 0;
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rs.j = 0;
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}
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static inline void
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arc4_addrandom(u_char *dat, int datlen)
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{
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int n;
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u_int8_t si;
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rs.i--;
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for (n = 0; n < 256; n++) {
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rs.i = (rs.i + 1);
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si = rs.s[rs.i];
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rs.j = (rs.j + si + dat[n % datlen]);
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rs.s[rs.i] = rs.s[rs.j];
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rs.s[rs.j] = si;
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}
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rs.j = rs.i;
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}
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size_t
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__arc4_sysctl(u_char *buf, size_t size)
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{
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int mib[2];
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size_t len, done;
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mib[0] = CTL_KERN;
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mib[1] = KERN_ARND;
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done = 0;
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do {
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len = size;
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if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
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return (done);
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done += len;
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buf += len;
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size -= len;
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} while (size > 0);
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return (done);
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}
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static void
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arc4_stir(void)
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{
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u_char rdat[KEYSIZE];
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int i;
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if (!rs_initialized) {
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arc4_init();
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rs_initialized = 1;
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}
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if (__arc4_sysctl(rdat, KEYSIZE) != KEYSIZE) {
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/*
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* The sysctl cannot fail. If it does fail on some FreeBSD
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* derivative or after some future change, just abort so that
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* the problem will be found and fixed. abort is not normally
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* suitable for a library but makes sense here.
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*/
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abort();
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}
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arc4_addrandom(rdat, KEYSIZE);
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/*
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* Discard early keystream, as per recommendations in:
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* "(Not So) Random Shuffles of RC4" by Ilya Mironov.
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*/
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for (i = 0; i < 3072; i++)
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(void)arc4_getbyte();
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arc4_count = 1600000;
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}
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static void
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arc4_stir_if_needed(void)
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{
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pid_t pid = getpid();
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if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) {
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arc4_stir_pid = pid;
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arc4_stir();
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}
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}
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static inline u_int8_t
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arc4_getbyte(void)
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{
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u_int8_t si, sj;
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rs.i = (rs.i + 1);
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si = rs.s[rs.i];
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rs.j = (rs.j + si);
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sj = rs.s[rs.j];
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rs.s[rs.i] = sj;
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rs.s[rs.j] = si;
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return (rs.s[(si + sj) & 0xff]);
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}
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static inline u_int32_t
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arc4_getword(void)
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{
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u_int32_t val;
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val = arc4_getbyte() << 24;
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val |= arc4_getbyte() << 16;
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val |= arc4_getbyte() << 8;
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val |= arc4_getbyte();
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return val;
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}
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void
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arc4random_stir(void)
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{
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_ARC4_LOCK();
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arc4_stir();
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_ARC4_UNLOCK();
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}
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void
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arc4random_addrandom(u_char *dat, int datlen)
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{
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_ARC4_LOCK();
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if (!rs_initialized)
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arc4_stir();
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arc4_addrandom(dat, datlen);
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_ARC4_UNLOCK();
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}
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u_int32_t
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arc4random(void)
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{
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u_int32_t val;
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_ARC4_LOCK();
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arc4_count -= 4;
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arc4_stir_if_needed();
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val = arc4_getword();
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_ARC4_UNLOCK();
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return val;
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}
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void
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arc4random_buf(void *_buf, size_t n)
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{
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u_char *buf = (u_char *)_buf;
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_ARC4_LOCK();
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arc4_stir_if_needed();
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while (n--) {
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if (--arc4_count <= 0)
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arc4_stir();
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buf[n] = arc4_getbyte();
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}
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_ARC4_UNLOCK();
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}
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/*
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* Calculate a uniformly distributed random number less than upper_bound
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* avoiding "modulo bias".
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*
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* Uniformity is achieved by generating new random numbers until the one
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* returned is outside the range [0, 2**32 % upper_bound). This
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* guarantees the selected random number will be inside
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* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
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* after reduction modulo upper_bound.
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*/
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u_int32_t
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arc4random_uniform(u_int32_t upper_bound)
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{
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u_int32_t r, min;
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if (upper_bound < 2)
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return 0;
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/* 2**32 % x == (2**32 - x) % x */
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min = -upper_bound % upper_bound;
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/*
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* This could theoretically loop forever but each retry has
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* p > 0.5 (worst case, usually far better) of selecting a
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* number inside the range we need, so it should rarely need
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* to re-roll.
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*/
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for (;;) {
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r = arc4random();
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if (r >= min)
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break;
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}
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return r % upper_bound;
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}
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#if 0
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/*-------- Test code for i386 --------*/
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#include <stdio.h>
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#include <machine/pctr.h>
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int
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main(int argc, char **argv)
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{
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const int iter = 1000000;
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int i;
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pctrval v;
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v = rdtsc();
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for (i = 0; i < iter; i++)
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arc4random();
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v = rdtsc() - v;
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v /= iter;
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printf("%qd cycles\n", v);
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}
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#endif
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