1 /*
2 * Copyright (C) 2018 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 <errno.h>
30 #include <fcntl.h>
31 #include <sys/random.h>
32 #include <unistd.h>
33
34 #include "private/ScopedFd.h"
35
getentropy_urandom(void * buffer,size_t buffer_size,int saved_errno)36 static int getentropy_urandom(void* buffer, size_t buffer_size, int saved_errno) {
37 ScopedFd fd(TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY | O_NOFOLLOW | O_CLOEXEC, 0)));
38 if (fd.get() == -1) return -1;
39
40 size_t collected = 0;
41 while (collected < buffer_size) {
42 ssize_t count = TEMP_FAILURE_RETRY(read(fd.get(), static_cast<char*>(buffer) + collected,
43 buffer_size - collected));
44 if (count == -1) return -1;
45 collected += count;
46 }
47
48 errno = saved_errno;
49 return 0;
50 }
51
getentropy(void * buffer,size_t buffer_size)52 int getentropy(void* buffer, size_t buffer_size) {
53 if (buffer_size > 256) {
54 errno = EIO;
55 return -1;
56 }
57
58 int saved_errno = errno;
59
60 size_t collected = 0;
61 while (collected < buffer_size) {
62 long count = TEMP_FAILURE_RETRY(getrandom(static_cast<char*>(buffer) + collected,
63 buffer_size - collected, GRND_NONBLOCK));
64 if (count == -1) {
65 // EAGAIN: there isn't enough entropy right now.
66 // ENOSYS/EINVAL: getrandom(2) or GRND_NONBLOCK isn't supported.
67 // EFAULT: `buffer` is invalid.
68 // Try /dev/urandom regardless because it can't hurt,
69 // and we don't need to optimize the EFAULT case.
70 // See http://b/33059407 and http://b/67015565.
71 return getentropy_urandom(buffer, buffer_size, saved_errno);
72 }
73 collected += count;
74 }
75
76 errno = saved_errno;
77 return 0;
78 }
79