1 /* 2 * Copyright (C) 2016 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include "private/bionic_arc4random.h" 30 31 #include <stdlib.h> 32 #include <string.h> 33 #include <sys/auxv.h> 34 #include <unistd.h> 35 36 #include <async_safe/log.h> 37 38 #include "private/KernelArgumentBlock.h" 39 40 void __libc_safe_arc4random_buf(void* buf, size_t n, KernelArgumentBlock& args) { 41 // Only call arc4random_buf once we have `/dev/urandom` because getentropy(3) 42 // will fall back to using `/dev/urandom` if getrandom(2) fails, and abort if 43 // if can't use `/dev/urandom`. 44 static bool have_urandom = access("/dev/urandom", R_OK) == 0; 45 if (have_urandom) { 46 arc4random_buf(buf, n); 47 return; 48 } 49 50 static size_t at_random_bytes_consumed = 0; 51 if (at_random_bytes_consumed + n > 16) { 52 async_safe_fatal("ran out of AT_RANDOM bytes, have %zu, requested %zu", 53 16 - at_random_bytes_consumed, n); 54 } 55 56 memcpy(buf, reinterpret_cast<char*>(args.getauxval(AT_RANDOM)) + at_random_bytes_consumed, n); 57 at_random_bytes_consumed += n; 58 return; 59 } 60
