mirror of
https://codeberg.org/libreboot/lbmk.git
synced 2026-07-11 14:02:52 +02:00
Leah Rowe
6c8cf9a9e0
build-time option. do not allow fallback; on a system where getrandom is used, it should be used exclusively. on some systems, getrandom may not be available, even if they have a newer kernel. Signed-off-by: Leah Rowe <leah@libreboot.org>
142 lines
2.9 KiB
C
142 lines
2.9 KiB
C
/* SPDX-License-Identifier: MIT
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* Copyright (c) 2026 Leah Rowe <leah@libreboot.org>
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*
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* Random number generation
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*/
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#ifndef RAND_H
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#define RAND_H
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#ifdef __OpenBSD__
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#include <sys/param.h>
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#endif
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#include <sys/types.h>
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#include <errno.h>
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#if !((defined(__OpenBSD__) && (OpenBSD) >= 201) || \
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defined(__FreeBSD__) || \
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defined(__NetBSD__) || defined(__APPLE__))
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#include <fcntl.h> /* if not arc4random: /dev/urandom */
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#endif
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#include <limits.h>
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#include <stddef.h>
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#include <string.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include "../include/common.h"
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/* Random numbers
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*/
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/* when calling this: save errno
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* first, then set errno to zero.
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* on error, this function will
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* set errno and possibly return
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*
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* rlong also preserves errno
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* and leaves it unchanged on
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* success, so if you do it
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* right, you can detect error.
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* this is because it uses
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* /dev/urandom which can err.
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* ditto getrandom (EINTR),
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* theoretically.
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*/
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/* for the linux version: we use only the
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* syscall, because we cannot trust /dev/urandom
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* to be as robust, and some libc implementations
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* may default to /dev/urandom under fault conditions.
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*
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* for general high reliability, we must abort on
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* failure. in practise, it will likely never fail.
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* the arc4random call on bsd never returns error.
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*/
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size_t
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rlong(void)
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{
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size_t rval;
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int saved_errno = errno;
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#if (defined(__OpenBSD__) || defined(__FreeBSD__) || \
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defined(__NetBSD__) || defined(__APPLE__) || \
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defined(__DragonFly__))
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arc4random_buf(&rval, sizeof(size_t));
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goto out;
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#elif defined(USE_URANDOM) && \
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((USE_URANDOM) > 0)
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/* Use of /dev/urandom is ill advised, due
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to FD exhaustion */
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int fd = -1;
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ssize_t rc = 0;
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errno = 0;
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if ((fd = open("/dev/urandom", O_RDONLY)) < 0)
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goto err;
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retry_rand:
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if ((rc = read(fd, &rval, sizeof(rval))) < 0) {
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if (errno == EINTR || errno == EAGAIN)
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goto retry_rand;
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goto err;
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}
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if ((rval += (size_t)rc) < sizeof(rval))
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goto retry_rand;
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#elif defined(__linux__)
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size_t off = 0;
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size_t len = sizeof(rval);
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ssize_t rc;
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errno = 0;
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retry_rand:
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rc = (ssize_t)syscall(SYS_getrandom,
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(char *)&rval + off, len - off, 0);
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if (rc < 0) {
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if (errno == EINTR || errno == EAGAIN) {
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usleep(100);
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goto retry_rand;
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}
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goto err; /* possibly unsupported by kernel */
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}
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if ((off += (size_t)rc) < len)
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goto retry_rand;
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goto out;
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#else
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#error Unsupported operating system (possibly unsecure randomisation)
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#endif
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out:
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errno = saved_errno;
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return rval;
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err:
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/*
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* getrandom can return with error, but arc4random
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* doesn't. generally, getrandom will be reliable,
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* but we of course have to maintain parity with
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* BSD. So a rand failure is to be interpreted as
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* a major systems failure, and we act accordingly.
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*/
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err_no_cleanup(1, ECANCELED,
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"Randomisation failure, possibly unsupported in your kernel.");
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exit(EXIT_FAILURE);
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return 0;
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}
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#endif
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