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/*
* Copyright (C) 2016 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 "private/bionic_arc4random.h"
#include <stdlib.h>
#include <string.h>
#include <sys/auxv.h>
#include <unistd.h>
#include <async_safe/log.h>
void __libc_safe_arc4random_buf(void* buf, size_t n) {
// Only call arc4random_buf once we have `/dev/urandom` because getentropy(3)
// will fall back to using `/dev/urandom` if getrandom(2) fails, and abort if
// if can't use `/dev/urandom`.
static bool have_urandom = access("/dev/urandom", R_OK) == 0;
if (have_urandom) {
arc4random_buf(buf, n);
return;
}
static size_t at_random_bytes_consumed = 0;
if (at_random_bytes_consumed + n > 16) {
async_safe_fatal("ran out of AT_RANDOM bytes, have %zu, requested %zu",
16 - at_random_bytes_consumed, n);
}
memcpy(buf, reinterpret_cast<char*>(getauxval(AT_RANDOM)) + at_random_bytes_consumed, n);
at_random_bytes_consumed += n;
return;
}
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