mirror of
https://codeberg.org/libreboot/lbmk.git
synced 2026-07-11 14:02:52 +02:00
Leah Rowe
136 lines
3.2 KiB
C
136 lines
3.2 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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#ifndef USE_URANDOM
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#define USE_URANDOM 0
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#endif
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#include <errno.h>
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#if defined(USE_URANDOM) && \
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((USE_URANDOM) > 0)
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#include <fcntl.h> /* if not arc4random: /dev/urandom */
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#endif
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#include <fcntl.h>
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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 <string.h>
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#include "../include/common.h"
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/* Regarding Linux getrandom/urandom:
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*
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* For maximum security guarantee, we *only*
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* use getrandom via syscall, or /dev/urandom;
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* use of urandom is ill advised. This is why
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* we use the syscall, in case the libc version
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* of getrandom() might defer to /dev/urandom
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*
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* We *abort* on error, for both /dev/urandom
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* and getrandom(), because the BSD arc4random
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* never returns with error; therefore, for the
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* most parity in terms of behaviour, we abort,
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* because otherwise the function would have two
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* return modes: always successful (BSD), or only
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* sometimes (Linux). The BSD arc4random could
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* theoretically abort; it is extremely unlikely
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* there, and just so on Linux, hence this design.
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*
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* This is important, because cryptographic code
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* for example must not rely on weak randomness.
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* We must therefore treat broken randomness as
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* though the world is broken, and burn accordingly.
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*
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* Similarly, any invalid input (NULL, zero bytes
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* requested) are treated as fatal errors; again,
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* cryptographic code must be reliable. If your
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* code erroneously requested zero bytes, you might
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* then end up with a non-randomised buffer, where
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* you likely intended otherwise.
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*
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* In other words: call rset() correctly, or your
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* program dies, and rset will behave correctly,
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* or your program dies.
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*/
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void
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rset(void *buf, size_t n)
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{
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int saved_errno = errno;
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if (if_err(buf == NULL, EFAULT))
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goto err;
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if (n == 0)
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err_no_cleanup(0, EPERM,
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"rset: zero-byte length request");
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#if (defined(__OpenBSD__) || defined(__FreeBSD__) || \
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defined(__NetBSD__) || defined(__APPLE__) || \
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defined(__DragonFly__)) && !(defined(USE_URANDOM) && \
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((USE_URANDOM) > 0))
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arc4random_buf(buf, n);
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goto out;
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#else
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size_t off = 0;
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ssize_t rc = 0;
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#if defined(USE_URANDOM) && \
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((USE_URANDOM) > 0)
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int fd = -1;
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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, (unsigned char *)buf + off, n - off)) < 0) {
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#elif defined(__linux__)
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retry_rand:
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if ((rc = (ssize_t)syscall(SYS_getrandom,
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(unsigned char *)buf + off, n - off, 0)) < 0) {
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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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if (errno == EINTR ||
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errno == EAGAIN)
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goto retry_rand;
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goto err; /* possibly unsupported by kernel */
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}
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if (rc == 0)
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goto err; /* prevent infinite loop on fatal err */
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if ((off += (size_t)rc) < n)
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goto retry_rand;
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#if defined(USE_URANDOM) && \
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((USE_URANDOM) > 0)
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close_no_err(&fd);
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#endif
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goto out;
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#endif
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out:
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errno = saved_errno;
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return;
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err:
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err_no_cleanup(0, ECANCELED,
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"Randomisation failure, possibly unsupported in your kernel");
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exit(EXIT_FAILURE);
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}
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#endif
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