1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 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. 15 * 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 26 * SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/random.h> 34 35 #include <errno.h> 36 #include <stdlib.h> 37 38 #include "libc_private.h" 39 40 /* 41 * If a newer libc is accidentally installed on an older kernel, provide high 42 * quality random data anyway. The sysctl interface is not as fast and does 43 * not block by itself, but is provided by even very old kernels. 44 */ 45 static int 46 getentropy_fallback(void *buf, size_t buflen) 47 { 48 /* 49 * oldp (buf) == NULL has a special meaning for sysctl that results in 50 * no EFAULT. For compatibility with the kernel getrandom(2), detect 51 * this case and return the appropriate error. 52 */ 53 if (buf == NULL && buflen > 0) { 54 errno = EFAULT; 55 return (-1); 56 } 57 if (__arc4_sysctl(buf, buflen) != buflen) { 58 if (errno == EFAULT) 59 return (-1); 60 /* 61 * This cannot happen. _arc4_sysctl() spins until the random 62 * device is seeded and then repeatedly reads until the full 63 * request is satisfied. The only way for this to return a zero 64 * byte or short read is if sysctl(2) on the kern.arandom MIB 65 * fails. In this case, exceping the user-provided-a-bogus- 66 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir). 67 */ 68 abort(); 69 } 70 return (0); 71 } 72 73 int 74 getentropy(void *buf, size_t buflen) 75 { 76 ssize_t rd; 77 78 if (buflen > 256) { 79 errno = EIO; 80 return (-1); 81 } 82 83 while (buflen > 0) { 84 rd = getrandom(buf, buflen, 0); 85 if (rd == -1) { 86 if (errno == EINTR) 87 continue; 88 else if (errno == ENOSYS) 89 return (getentropy_fallback(buf, buflen)); 90 else 91 return (-1); 92 } 93 94 /* This cannot happen. */ 95 if (rd == 0) 96 abort(); 97 98 buf = (char *)buf + rd; 99 buflen -= rd; 100 } 101 102 return (0); 103 } 104