2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
32 #include <sys/param.h>
33 #include <sys/random.h>
34 #include <sys/sysctl.h>
41 #include "libc_private.h"
43 /* First __FreeBSD_version bump after introduction of getrandom(2) (r331279) */
44 #define GETRANDOM_FIRST 1200061
46 extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t);
49 _getentropy_fail(void)
55 arnd_sysctl(u_char *buf, size_t size)
66 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
77 * If a newer libc is accidentally installed on an older kernel, provide high
78 * quality random data anyway. The sysctl interface is not as fast and does
79 * not block by itself, but is provided by even very old kernels.
82 getentropy_fallback(void *buf, size_t buflen)
85 * oldp (buf) == NULL has a special meaning for sysctl that results in
86 * no EFAULT. For compatibility with the kernel getrandom(2), detect
87 * this case and return the appropriate error.
89 if (buf == NULL && buflen > 0) {
93 if (arnd_sysctl(buf, buflen) != buflen) {
97 * This cannot happen. arnd_sysctl() spins until the random
98 * device is seeded and then repeatedly reads until the full
99 * request is satisfied. The only way for this to return a zero
100 * byte or short read is if sysctl(2) on the kern.arandom MIB
101 * fails. In this case, excepting the user-provided-a-bogus-
102 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir).
110 getentropy(void *buf, size_t buflen)
120 have_getrandom = (__getosreldate() >= GETRANDOM_FIRST);
123 if (have_getrandom) {
124 rd = getrandom(buf, buflen, 0);
129 * Kernel >= r331280 and < r337999
130 * will return ECAPMODE when the
131 * caller is already in capability
132 * mode, fallback to traditional
133 * method in this case.
135 have_getrandom = false;
146 return (getentropy_fallback(buf, buflen));
149 /* This cannot happen. */
153 buf = (char *)buf + rd;