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util-linux/lib/randutils.c

245 lines
5.3 KiB

/*
* SPDX-License-Identifier: BSD-3-Clause
*
* General purpose random utilities. Based on libuuid code.
*
* This code is free software; you can redistribute it and/or modify it under
* the terms of the Modified BSD License. The complete text of the license is
* available in the Documentation/licenses/COPYING.BSD-3-Clause file.
*/
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#ifdef HAVE_SYS_SYSCALL_H
#include <sys/syscall.h>
#endif
#include "c.h"
#include "randutils.h"
#include "nls.h"
#ifdef HAVE_TLS
#define THREAD_LOCAL static __thread
#else
#define THREAD_LOCAL static
#endif
#ifdef HAVE_GETRANDOM
# include <sys/random.h>
#elif defined (__linux__)
# if !defined(SYS_getrandom) && defined(__NR_getrandom)
/* usable kernel-headers, but old glibc-headers */
# define SYS_getrandom __NR_getrandom
# endif
#endif
#if !defined(HAVE_GETRANDOM) && defined(SYS_getrandom)
/* libc without function, but we have syscall */
#define GRND_NONBLOCK 0x01
#define GRND_RANDOM 0x02
static int getrandom(void *buf, size_t buflen, unsigned int flags)
{
return (syscall(SYS_getrandom, buf, buflen, flags));
}
# define HAVE_GETRANDOM
#endif
#if defined(__linux__) && defined(__NR_gettid) && defined(HAVE_JRAND48)
#define DO_JRAND_MIX
THREAD_LOCAL unsigned short ul_jrand_seed[3];
#endif
int rand_get_number(int low_n, int high_n)
{
return rand() % (high_n - low_n + 1) + low_n;
}
static void crank_random(void)
{
int i;
struct timeval tv;
unsigned int n_pid, n_uid;
gettimeofday(&tv, NULL);
n_pid = getpid();
n_uid = getuid();
srand((n_pid << 16) ^ n_uid ^ tv.tv_sec ^ tv.tv_usec);
#ifdef DO_JRAND_MIX
ul_jrand_seed[0] = getpid() ^ (tv.tv_sec & 0xFFFF);
ul_jrand_seed[1] = getppid() ^ (tv.tv_usec & 0xFFFF);
ul_jrand_seed[2] = (tv.tv_sec ^ tv.tv_usec) >> 16;
#endif
/* Crank the random number generator a few times */
gettimeofday(&tv, NULL);
for (i = (tv.tv_sec ^ tv.tv_usec) & 0x1F; i > 0; i--)
rand();
}
int random_get_fd(void)
{
int i, fd;
fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
if (fd == -1)
fd = open("/dev/random", O_RDONLY | O_NONBLOCK | O_CLOEXEC);
if (fd >= 0) {
i = fcntl(fd, F_GETFD);
if (i >= 0)
fcntl(fd, F_SETFD, i | FD_CLOEXEC);
}
crank_random();
return fd;
}
/*
* Generate a stream of random nbytes into buf.
* Use /dev/urandom if possible, and if not,
* use glibc pseudo-random functions.
*/
#define UL_RAND_READ_ATTEMPTS 8
#define UL_RAND_READ_DELAY 125000 /* microseconds */
/*
* Write @nbytes random bytes into @buf.
*
* Returns 0 for good quality of random bytes or 1 for weak quality.
*/
int ul_random_get_bytes(void *buf, size_t nbytes)
{
unsigned char *cp = (unsigned char *)buf;
size_t i, n = nbytes;
int lose_counter = 0;
#ifdef HAVE_GETRANDOM
while (n > 0) {
int x;
errno = 0;
x = getrandom(cp, n, GRND_NONBLOCK);
if (x > 0) { /* success */
n -= x;
cp += x;
lose_counter = 0;
errno = 0;
} else if (errno == ENOSYS) { /* kernel without getrandom() */
break;
} else if (errno == EAGAIN && lose_counter < UL_RAND_READ_ATTEMPTS) {
xusleep(UL_RAND_READ_DELAY); /* no entropy, wait and try again */
lose_counter++;
} else
break;
}
if (errno == ENOSYS)
#endif
/*
* We've been built against headers that support getrandom, but the
* running kernel does not. Fallback to reading from /dev/{u,}random
* as before
*/
{
int fd = random_get_fd();
lose_counter = 0;
if (fd >= 0) {
while (n > 0) {
ssize_t x = read(fd, cp, n);
if (x <= 0) {
if (lose_counter++ > UL_RAND_READ_ATTEMPTS)
break;
xusleep(UL_RAND_READ_DELAY);
continue;
}
n -= x;
cp += x;
lose_counter = 0;
}
close(fd);
}
}
/*
* We do this all the time, but this is the only source of
* randomness if /dev/random/urandom is out to lunch.
*/
crank_random();
for (cp = buf, i = 0; i < nbytes; i++)
*cp++ ^= (rand() >> 7) & 0xFF;
#ifdef DO_JRAND_MIX
{
unsigned short tmp_seed[3];
memcpy(tmp_seed, ul_jrand_seed, sizeof(tmp_seed));
ul_jrand_seed[2] = ul_jrand_seed[2] ^ syscall(__NR_gettid);
for (cp = buf, i = 0; i < nbytes; i++)
*cp++ ^= (jrand48(tmp_seed) >> 7) & 0xFF;
memcpy(ul_jrand_seed, tmp_seed,
sizeof(ul_jrand_seed)-sizeof(unsigned short));
}
#endif
return n != 0;
}
/*
* Tell source of randomness.
*/
const char *random_tell_source(void)
{
#ifdef HAVE_GETRANDOM
return _("getrandom() function");
#else
size_t i;
static const char *random_sources[] = {
"/dev/urandom",
"/dev/random"
};
for (i = 0; i < ARRAY_SIZE(random_sources); i++) {
if (!access(random_sources[i], R_OK))
return random_sources[i];
}
#endif
return _("libc pseudo-random functions");
}
#ifdef TEST_PROGRAM_RANDUTILS
#include <inttypes.h>
int main(int argc, char *argv[])
{
size_t i, n;
int64_t *vp, v;
char *buf;
size_t bufsz;
n = argc == 1 ? 16 : atoi(argv[1]);
printf("Multiple random calls:\n");
for (i = 0; i < n; i++) {
ul_random_get_bytes(&v, sizeof(v));
printf("#%02zu: %25"PRIu64"\n", i, v);
}
printf("One random call:\n");
bufsz = n * sizeof(*vp);
buf = malloc(bufsz);
if (!buf)
err(EXIT_FAILURE, "failed to allocate buffer");
ul_random_get_bytes(buf, bufsz);
for (i = 0; i < n; i++) {
vp = (int64_t *) (buf + (i * sizeof(*vp)));
printf("#%02zu: %25"PRIu64"\n", i, *vp);
}
return EXIT_SUCCESS;
}
#endif /* TEST_PROGRAM_RANDUTILS */