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git.ipfire.org Git - thirdparty/systemd.git/blob - src/basic/random-util.c
2 This file is part of systemd.
4 Copyright 2010 Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
26 #include <linux/random.h>
29 #ifdef HAVE_SYS_AUXV_H
36 #include "random-util.h"
37 #include "time-util.h"
39 int dev_urandom(void *p
, size_t n
) {
40 static int have_syscall
= -1;
42 _cleanup_close_
int fd
= -1;
45 /* Gathers some randomness from the kernel. This call will
46 * never block, and will always return some data from the
47 * kernel, regardless if the random pool is fully initialized
48 * or not. It thus makes no guarantee for the quality of the
49 * returned entropy, but is good enough for our usual usecases
50 * of seeding the hash functions for hashtable */
52 /* Use the getrandom() syscall unless we know we don't have
53 * it, or when the requested size is too large for it. */
54 if (have_syscall
!= 0 || (size_t) (int) n
!= n
) {
55 r
= getrandom(p
, n
, GRND_NONBLOCK
);
63 /* we lack the syscall, continue with
64 * reading from /dev/urandom */
66 else if (errno
== EAGAIN
)
67 /* not enough entropy for now. Let's
68 * remember to use the syscall the
69 * next time, again, but also read
70 * from /dev/urandom for now, which
71 * doesn't care about the current
72 * amount of entropy. */
81 fd
= open("/dev/urandom", O_RDONLY
|O_CLOEXEC
|O_NOCTTY
);
83 return errno
== ENOENT
? -ENOSYS
: -errno
;
85 return loop_read_exact(fd
, p
, n
, true);
88 void initialize_srand(void) {
89 static bool srand_called
= false;
91 #ifdef HAVE_SYS_AUXV_H
98 #ifdef HAVE_SYS_AUXV_H
99 /* The kernel provides us with 16 bytes of entropy in auxv, so let's try to make use of that to seed the
100 * pseudo-random generator. It's better than nothing... */
102 auxv
= (void*) getauxval(AT_RANDOM
);
104 assert_cc(sizeof(x
) < 16);
105 memcpy(&x
, auxv
, sizeof(x
));
111 x
^= (unsigned) now(CLOCK_REALTIME
);
112 x
^= (unsigned) gettid();
118 void random_bytes(void *p
, size_t n
) {
122 r
= dev_urandom(p
, n
);
126 /* If some idiot made /dev/urandom unavailable to us, he'll
127 * get a PRNG instead. */
131 for (q
= p
; q
< (uint8_t*) p
+ n
; q
++)