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/***
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <sys/time.h>
#include <linux/random.h>
#include <stdint.h>
#ifdef HAVE_SYS_AUXV_H
#include <sys/auxv.h>
#endif
#include "fd-util.h"
#include "io-util.h"
#include "missing.h"
#include "random-util.h"
#include "time-util.h"
int dev_urandom(void *p, size_t n) {
static int have_syscall = -1;
_cleanup_close_ int fd = -1;
int r;
/* Gathers some randomness from the kernel. This call will
* never block, and will always return some data from the
* kernel, regardless if the random pool is fully initialized
* or not. It thus makes no guarantee for the quality of the
* returned entropy, but is good enough for or usual usecases
* of seeding the hash functions for hashtable */
/* Use the getrandom() syscall unless we know we don't have
* it, or when the requested size is too large for it. */
if (have_syscall != 0 || (size_t) (int) n != n) {
r = getrandom(p, n, GRND_NONBLOCK);
if (r == (int) n) {
have_syscall = true;
return 0;
}
if (r < 0) {
if (errno == ENOSYS)
/* we lack the syscall, continue with
* reading from /dev/urandom */
have_syscall = false;
else if (errno == EAGAIN)
/* not enough entropy for now. Let's
* remember to use the syscall the
* next time, again, but also read
* from /dev/urandom for now, which
* doesn't care about the current
* amount of entropy. */
have_syscall = true;
else
return -errno;
} else
/* too short read? */
return -ENODATA;
}
fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (fd < 0)
return errno == ENOENT ? -ENOSYS : -errno;
return loop_read_exact(fd, p, n, true);
}
void initialize_srand(void) {
static bool srand_called = false;
unsigned x;
#ifdef HAVE_SYS_AUXV_H
void *auxv;
#endif
if (srand_called)
return;
#ifdef HAVE_SYS_AUXV_H
/* The kernel provides us with 16 bytes of entropy in auxv, so let's try to make use of that to seed the
* pseudo-random generator. It's better than nothing... */
auxv = (void*) getauxval(AT_RANDOM);
if (auxv) {
assert_cc(sizeof(x) < 16);
memcpy(&x, auxv, sizeof(x));
} else
#endif
x = 0;
x ^= (unsigned) now(CLOCK_REALTIME);
x ^= (unsigned) gettid();
srand(x);
srand_called = true;
}
void random_bytes(void *p, size_t n) {
uint8_t *q;
int r;
r = dev_urandom(p, n);
if (r >= 0)
return;
/* If some idiot made /dev/urandom unavailable to us, he'll
* get a PRNG instead. */
initialize_srand();
for (q = p; q < (uint8_t*) p + n; q ++)
*q = rand();
}
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