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/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
*/
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "dbg.h"
#ifdef __linux__
#include <sys/syscall.h>
#endif
#ifdef __APPLE__
#include <AvailabilityMacros.h>
#ifndef MAC_OS_X_VERSION_10_12
#define MAC_OS_X_VERSION_10_12 101200
#endif
#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_12
#include <sys/random.h>
#endif
#endif
static inline bool __attribute__((__warn_unused_result__))
get_random_bytes(uint8_t *out, size_t len)
{
ssize_t ret = 0;
size_t i;
int fd;
if (len > 256) {
errno = EOVERFLOW;
return false;
}
#if defined(__OpenBSD__) || \
(defined(__APPLE__) && \
MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_12) || \
(defined(__GLIBC__) && \
(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25)))
if (!getentropy(out, len))
return true;
#endif
#if defined(__NR_getrandom) && defined(__linux__)
if (syscall(__NR_getrandom, out, len, 0) == (ssize_t)len)
return true;
#endif
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0)
return false;
for (errno = 0, i = 0; i < len; i += ret, ret = 0) {
ret = read(fd, out + i, len - i);
if (ret <= 0) {
ret = errno ? -errno : -EIO;
break;
}
}
close(fd);
errno = -ret;
return i == len;
}
uint64_t random_bounded(uint64_t bound)
{
uint64_t ret;
if (bound == 0)
return 0;
if (bound == 1) {
if (!get_random_bytes((uint8_t *)&ret, sizeof(ret)))
fatal("get_random_bytes()");
return (ret > 0x7FFFFFFFFFFFFFFF) ? 1 : 0;
}
const uint64_t max_mod_bound = (1 + ~bound) % bound;
do {
if (!get_random_bytes((uint8_t *)&ret, sizeof(ret)))
fatal("get_random_bytes()");
} while (ret < max_mod_bound);
return ret % bound;
}
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