mirror of
https://codeberg.org/libreboot/lbmk.git
synced 2026-07-11 05:52:36 +02:00
Leah Rowe
154 lines
3.5 KiB
C
154 lines
3.5 KiB
C
/* SPDX-License-Identifier: MIT
|
|
* Copyright (c) 2026 Leah Rowe <leah@libreboot.org>
|
|
*
|
|
* Random number generation
|
|
*/
|
|
|
|
#ifndef RAND_H
|
|
#define RAND_H
|
|
|
|
#ifdef __OpenBSD__
|
|
#include <sys/param.h>
|
|
#endif
|
|
#include <sys/types.h>
|
|
|
|
#ifndef USE_URANDOM
|
|
#define USE_URANDOM 0
|
|
#endif
|
|
|
|
#include <errno.h>
|
|
#if defined(USE_URANDOM) && \
|
|
((USE_URANDOM) > 0)
|
|
#include <fcntl.h> /* if not arc4random: /dev/urandom */
|
|
#endif
|
|
|
|
#include <fcntl.h>
|
|
#include <limits.h>
|
|
#include <stddef.h>
|
|
#include <string.h>
|
|
#include <unistd.h>
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
|
|
#include "../include/common.h"
|
|
|
|
/* Regarding Linux getrandom/urandom:
|
|
*
|
|
* For maximum security guarantee, we *only*
|
|
* use getrandom via syscall, or /dev/urandom;
|
|
* use of urandom is ill advised. This is why
|
|
* we use the syscall, in case the libc version
|
|
* of getrandom() might defer to /dev/urandom
|
|
*
|
|
* We *abort* on error, for both /dev/urandom
|
|
* and getrandom(), because the BSD arc4random
|
|
* never returns with error; therefore, for the
|
|
* most parity in terms of behaviour, we abort,
|
|
* because otherwise the function would have two
|
|
* return modes: always successful (BSD), or only
|
|
* sometimes (Linux). The BSD arc4random could
|
|
* theoretically abort; it is extremely unlikely
|
|
* there, and just so on Linux, hence this design.
|
|
*
|
|
* This is important, because cryptographic code
|
|
* for example must not rely on weak randomness.
|
|
* We must therefore treat broken randomness as
|
|
* though the world is broken, and burn accordingly.
|
|
*
|
|
* Similarly, any invalid input (NULL, zero bytes
|
|
* requested) are treated as fatal errors; again,
|
|
* cryptographic code must be reliable. If your
|
|
* code erroneously requested zero bytes, you might
|
|
* then end up with a non-randomised buffer, where
|
|
* you likely intended otherwise.
|
|
*
|
|
* In other words: call rset() correctly, or your
|
|
* program dies, and rset will behave correctly,
|
|
* or your program dies.
|
|
*/
|
|
|
|
void *
|
|
mkrbuf(size_t n)
|
|
{
|
|
void *buf;
|
|
|
|
if (n == 0)
|
|
err_no_cleanup(0, EPERM, "mkrbuf: zero-byte request");
|
|
|
|
if ((buf = malloc(n)) == NULL)
|
|
err_no_cleanup(0, ENOMEM, "mkrbuf: malloc");
|
|
|
|
rset(buf, n);
|
|
return buf; /* basically malloc() but with rand */
|
|
}
|
|
|
|
void
|
|
rset(void *buf, size_t n)
|
|
{
|
|
int saved_errno = errno;
|
|
|
|
if (if_err(buf == NULL, EFAULT))
|
|
goto err;
|
|
|
|
if (n == 0)
|
|
err_no_cleanup(0, EPERM, "rset: zero-byte request");
|
|
|
|
#if (defined(__OpenBSD__) || defined(__FreeBSD__) || \
|
|
defined(__NetBSD__) || defined(__APPLE__) || \
|
|
defined(__DragonFly__)) && !(defined(USE_URANDOM) && \
|
|
((USE_URANDOM) > 0))
|
|
|
|
arc4random_buf(buf, n);
|
|
goto out;
|
|
#else
|
|
size_t off = 0;
|
|
ssize_t rc = 0;
|
|
|
|
#if defined(USE_URANDOM) && \
|
|
((USE_URANDOM) > 0)
|
|
int fd = -1;
|
|
|
|
if ((fd = open("/dev/urandom", O_RDONLY)) < 0)
|
|
goto err;
|
|
retry_rand:
|
|
if ((rc = read(fd, (unsigned char *)buf + off, n - off)) < 0) {
|
|
#elif defined(__linux__)
|
|
retry_rand:
|
|
if ((rc = (ssize_t)syscall(SYS_getrandom,
|
|
(unsigned char *)buf + off, n - off, 0)) < 0) {
|
|
#else
|
|
#error Unsupported operating system (possibly unsecure randomisation)
|
|
#endif
|
|
if (errno == EINTR ||
|
|
errno == EAGAIN)
|
|
goto retry_rand;
|
|
|
|
goto err; /* possibly unsupported by kernel */
|
|
}
|
|
|
|
if (rc == 0)
|
|
goto err; /* prevent infinite loop on fatal err */
|
|
|
|
if ((off += (size_t)rc) < n)
|
|
goto retry_rand;
|
|
|
|
#if defined(USE_URANDOM) && \
|
|
((USE_URANDOM) > 0)
|
|
close_no_err(&fd);
|
|
#endif
|
|
goto out;
|
|
#endif
|
|
out:
|
|
errno = saved_errno;
|
|
return;
|
|
err:
|
|
#if defined(USE_URANDOM) && \
|
|
((USE_URANDOM) > 0)
|
|
close_no_err(&fd);
|
|
#endif
|
|
err_no_cleanup(0, ECANCELED,
|
|
"Randomisation failure, possibly unsupported in your kernel");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
#endif
|