5d13a15b1d
Double newlines (i.e. one empty lines) are great to structure code. But let's avoid triple newlines (i.e. two empty lines), quadruple newlines, quintuple newlines, …, that's just spurious whitespace. It's an easy way to drop 121 lines of code, and keeps the coding style of our sources a bit tigther.
160 lines
4.8 KiB
C
160 lines
4.8 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
|
|
/***
|
|
This file is part of systemd.
|
|
|
|
Copyright 2010 Lennart Poettering
|
|
***/
|
|
|
|
#include <elf.h>
|
|
#include <errno.h>
|
|
#include <fcntl.h>
|
|
#include <linux/random.h>
|
|
#include <stdbool.h>
|
|
#include <stdint.h>
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
#include <sys/time.h>
|
|
|
|
#if HAVE_SYS_AUXV_H
|
|
# include <sys/auxv.h>
|
|
#endif
|
|
|
|
#if USE_SYS_RANDOM_H
|
|
# include <sys/random.h>
|
|
#else
|
|
# include <linux/random.h>
|
|
#endif
|
|
|
|
#include "fd-util.h"
|
|
#include "io-util.h"
|
|
#include "missing.h"
|
|
#include "random-util.h"
|
|
#include "time-util.h"
|
|
|
|
int acquire_random_bytes(void *p, size_t n, bool high_quality_required) {
|
|
static int have_syscall = -1;
|
|
|
|
_cleanup_close_ int fd = -1;
|
|
unsigned already_done = 0;
|
|
int r;
|
|
|
|
/* Gathers some randomness from the kernel. This call will never block. If
|
|
* high_quality_required, it will always return some data from the kernel,
|
|
* regardless of whether the random pool is fully initialized or not.
|
|
* Otherwise, it will return success if at least some random bytes were
|
|
* successfully acquired, and an error if the kernel has no entropy whatsover
|
|
* for us. */
|
|
|
|
/* Use the getrandom() syscall unless we know we don't have it. */
|
|
if (have_syscall != 0) {
|
|
r = getrandom(p, n, GRND_NONBLOCK);
|
|
if (r > 0) {
|
|
have_syscall = true;
|
|
if ((size_t) r == n)
|
|
return 0;
|
|
if (!high_quality_required) {
|
|
/* Fill in the remaining bytes using pseudorandom values */
|
|
pseudorandom_bytes((uint8_t*) p + r, n - r);
|
|
return 0;
|
|
}
|
|
|
|
already_done = r;
|
|
} else if (errno == ENOSYS)
|
|
/* We lack the syscall, continue with reading from /dev/urandom. */
|
|
have_syscall = false;
|
|
else if (errno == EAGAIN) {
|
|
/* The kernel has no entropy whatsoever. Let's remember to
|
|
* use the syscall the next time again though.
|
|
*
|
|
* If high_quality_required is false, return an error so that
|
|
* random_bytes() can produce some pseudorandom
|
|
* bytes. Otherwise, fall back to /dev/urandom, which we know
|
|
* is empty, but the kernel will produce some bytes for us on
|
|
* a best-effort basis. */
|
|
have_syscall = true;
|
|
|
|
if (!high_quality_required)
|
|
return -ENODATA;
|
|
} else
|
|
return -errno;
|
|
}
|
|
|
|
fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
|
|
if (fd < 0)
|
|
return errno == ENOENT ? -ENOSYS : -errno;
|
|
|
|
return loop_read_exact(fd, (uint8_t*) p + already_done, n - already_done, true);
|
|
}
|
|
|
|
void initialize_srand(void) {
|
|
static bool srand_called = false;
|
|
unsigned x;
|
|
#if HAVE_SYS_AUXV_H
|
|
void *auxv;
|
|
#endif
|
|
|
|
if (srand_called)
|
|
return;
|
|
|
|
#if 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;
|
|
}
|
|
|
|
/* INT_MAX gives us only 31 bits, so use 24 out of that. */
|
|
#if RAND_MAX >= INT_MAX
|
|
# define RAND_STEP 3
|
|
#else
|
|
/* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */
|
|
# define RAND_STEP 1
|
|
#endif
|
|
|
|
void pseudorandom_bytes(void *p, size_t n) {
|
|
uint8_t *q;
|
|
|
|
initialize_srand();
|
|
|
|
for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) {
|
|
unsigned rr;
|
|
|
|
rr = (unsigned) rand();
|
|
|
|
#if RAND_STEP >= 3
|
|
if ((size_t) (q - (uint8_t*) p + 2) < n)
|
|
q[2] = rr >> 16;
|
|
#endif
|
|
#if RAND_STEP >= 2
|
|
if ((size_t) (q - (uint8_t*) p + 1) < n)
|
|
q[1] = rr >> 8;
|
|
#endif
|
|
q[0] = rr;
|
|
}
|
|
}
|
|
|
|
void random_bytes(void *p, size_t n) {
|
|
int r;
|
|
|
|
r = acquire_random_bytes(p, n, false);
|
|
if (r >= 0)
|
|
return;
|
|
|
|
/* If some idiot made /dev/urandom unavailable to us, or the
|
|
* kernel has no entropy, use a PRNG instead. */
|
|
return pseudorandom_bytes(p, n);
|
|
}
|