1/* Implementation of getentropy based on the getrandom system call.
2 Copyright (C) 2016-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sys/random.h>
20#include <assert.h>
21#include <errno.h>
22#include <unistd.h>
23
24/* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on
25 success and -1 on failure. */
26int
27getentropy (void *buffer, size_t length)
28{
29 /* The interface is documented to return EIO for buffer lengths
30 longer than 256 bytes. */
31 if (length > 256)
32 {
33 __set_errno (EIO);
34 return -1;
35 }
36
37 /* Try to fill the buffer completely. Even with the 256 byte limit
38 above, we might still receive an EINTR error (when blocking
39 during boot). */
40 void *end = buffer + length;
41 while (buffer < end)
42 {
43 /* NB: No cancellation point. */
44 ssize_t bytes = INLINE_SYSCALL_CALL (getrandom, buffer, end - buffer, 0);
45 if (bytes < 0)
46 {
47 if (errno == EINTR)
48 /* Try again if interrupted by a signal. */
49 continue;
50 else
51 return -1;
52 }
53 if (bytes == 0)
54 {
55 /* No more bytes available. This should not happen under
56 normal circumstances. */
57 __set_errno (EIO);
58 return -1;
59 }
60 /* Try again in case of a short read. */
61 buffer += bytes;
62 }
63 return 0;
64}
65