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 <errno.h> 32 #include <stdatomic.h> 33 #include <stdlib.h> 34 #include <sys/auxv.h> 35 #include <syscall.h> 36 #include <unistd.h> 37 38 #include "private/KernelArgumentBlock.h" 39 #include "private/libc_logging.h" 40 41 bool __libc_arc4random_has_unlimited_entropy() { 42 static bool have_urandom = access("/dev/urandom", R_OK) == 0; 43 return have_urandom; 44 } 45 46 void __libc_safe_arc4random_buf(void* buf, size_t n, KernelArgumentBlock& args) { 47 // Only call arc4random_buf once we `have_urandom', since in getentropy_getrandom we may fallback 48 // to use /dev/urandom, if the kernel entropy pool hasn't been initialized or not enough bytes 49 if (__libc_arc4random_has_unlimited_entropy()) { 50 arc4random_buf(buf, n); 51 return; 52 } 53 54 static size_t at_random_bytes_consumed = 0; 55 if (at_random_bytes_consumed + n > 16) { 56 __libc_fatal("ran out of AT_RANDOM bytes, have %zu, requested %zu", 57 16 - at_random_bytes_consumed, n); 58 } 59 60 memcpy(buf, reinterpret_cast<char*>(args.getauxval(AT_RANDOM)) + at_random_bytes_consumed, n); 61 at_random_bytes_consumed += n; 62 return; 63 } 64
