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/*
* Copyright (C) 2018 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <errno.h>
#include <fcntl.h>
#include <sys/random.h>
#include <unistd.h>
static int getentropy_urandom(void* buffer, size_t buffer_size, int saved_errno) {
int fd = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY | O_NOFOLLOW | O_CLOEXEC, 0));
if (fd == -1) return -1;
size_t collected = 0;
while (collected < buffer_size) {
ssize_t count = TEMP_FAILURE_RETRY(read(fd, static_cast<char*>(buffer) + collected,
buffer_size - collected));
if (count == -1) {
close(fd);
return -1;
}
collected += count;
}
close(fd);
errno = saved_errno;
return 0;
}
int getentropy(void* buffer, size_t buffer_size) {
if (buffer_size > 256) {
errno = EIO;
return -1;
}
int saved_errno = errno;
size_t collected = 0;
while (collected < buffer_size) {
long count = TEMP_FAILURE_RETRY(getrandom(static_cast<char*>(buffer) + collected,
buffer_size - collected, GRND_NONBLOCK));
if (count == -1) {
// EAGAIN: there isn't enough entropy right now.
// ENOSYS/EINVAL: getrandom(2) or GRND_NONBLOCK isn't supported.
// EFAULT: `buffer` is invalid.
// Try /dev/urandom regardless because it can't hurt,
// and we don't need to optimize the EFAULT case.
// See http://b/33059407 and http://b/67015565.
return getentropy_urandom(buffer, buffer_size, saved_errno);
}
collected += count;
}
errno = saved_errno;
return 0;
}
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