1/* Implementation of getentropy based on the getrandom system call.
2 Copyright (C) 2016-2023 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#include <sysdep.h>
24
25/* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on
26 success and -1 on failure. */
27int
28getentropy (void *buffer, size_t length)
29{
30 /* The interface is documented to return EIO for buffer lengths
31 longer than 256 bytes. */
32 if (length > 256)
33 {
34 __set_errno (EIO);
35 return -1;
36 }
37
38 /* Try to fill the buffer completely. Even with the 256 byte limit
39 above, we might still receive an EINTR error (when blocking
40 during boot). */
41 void *end = buffer + length;
42 while (buffer < end)
43 {
44 /* NB: No cancellation point. */
45 ssize_t bytes = INLINE_SYSCALL_CALL (getrandom, buffer, end - buffer, 0);
46 if (bytes < 0)
47 {
48 if (errno == EINTR)
49 /* Try again if interrupted by a signal. */
50 continue;
51 else
52 return -1;
53 }
54 if (bytes == 0)
55 {
56 /* No more bytes available. This should not happen under
57 normal circumstances. */
58 __set_errno (EIO);
59 return -1;
60 }
61 /* Try again in case of a short read. */
62 buffer += bytes;
63 }
64 return 0;
65}
66