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
__libc_arc4random_has_unlimited_entropy()41 bool __libc_arc4random_has_unlimited_entropy() {
42 static bool have_urandom = access("/dev/urandom", R_OK) == 0;
43 return have_urandom;
44 }
45
__libc_safe_arc4random_buf(void * buf,size_t n,KernelArgumentBlock & args)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