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/>.
22 #include <sys/types.h>
27 #include <linux/random.h>
29 #include "random-util.h"
30 #include "time-util.h"
34 int dev_urandom(void *p, size_t n) {
35 static int have_syscall = -1;
37 _cleanup_close_ int fd = -1;
40 /* Gathers some randomness from the kernel. This call will
41 * never block, and will always return some data from the
42 * kernel, regardless if the random pool is fully initialized
43 * or not. It thus makes no guarantee for the quality of the
44 * returned entropy, but is good enough for or usual usecases
45 * of seeding the hash functions for hashtable */
47 /* Use the getrandom() syscall unless we know we don't have
48 * it, or when the requested size is too large for it. */
49 if (have_syscall != 0 || (size_t) (int) n != n) {
50 r = getrandom(p, n, GRND_NONBLOCK);
58 /* we lack the syscall, continue with
59 * reading from /dev/urandom */
61 else if (errno == EAGAIN)
62 /* not enough entropy for now. Let's
63 * remember to use the syscall the
64 * next time, again, but also read
65 * from /dev/urandom for now, which
66 * doesn't care about the current
67 * amount of entropy. */
76 fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
78 return errno == ENOENT ? -ENOSYS : -errno;
80 return loop_read_exact(fd, p, n, true);
83 void initialize_srand(void) {
84 static bool srand_called = false;
86 #ifdef HAVE_SYS_AUXV_H
95 #ifdef HAVE_SYS_AUXV_H
96 /* The kernel provides us with a bit of entropy in auxv, so
97 * let's try to make use of that to seed the pseudo-random
98 * generator. It's better than nothing... */
100 auxv = (void*) getauxval(AT_RANDOM);
102 x ^= *(unsigned*) auxv;
105 x ^= (unsigned) now(CLOCK_REALTIME);
106 x ^= (unsigned) gettid();
112 void random_bytes(void *p, size_t n) {
116 r = dev_urandom(p, n);
120 /* If some idiot made /dev/urandom unavailable to us, he'll
121 * get a PRNG instead. */
125 for (q = p; q < (uint8_t*) p + n; q ++)