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92dcaa3e | 1 | /* Implementation of getentropy based on the getrandom system call. |
688903eb | 2 | Copyright (C) 2016-2018 Free Software Foundation, Inc. |
92dcaa3e FW |
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 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <sys/random.h> | |
20 | #include <assert.h> | |
21 | #include <errno.h> | |
22 | #include <unistd.h> | |
23 | ||
24 | #ifdef __NR_getrandom | |
25 | /* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on | |
26 | success and -1 on failure. */ | |
27 | int | |
28 | getentropy (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 | #else | |
67 | int | |
68 | getentropy (void *buffer, size_t length) | |
69 | { | |
70 | __set_errno (ENOSYS); | |
71 | return -1; | |
72 | } | |
73 | #endif |