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 #include <sys/sysctl.h> 35 36 #include <errno.h> 37 #include <stdbool.h> 38 #include <stdlib.h> 39 40 #include "libc_private.h" 41 42 /* First __FreeBSD_version bump after introduction of getrandom(2) (r331279) */ 43 #define GETRANDOM_FIRST 1200061 44 45 extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t); 46 47 static size_t 48 arnd_sysctl(u_char *buf, size_t size) 49 { 50 int mib[2]; 51 size_t len, done; 52 53 mib[0] = CTL_KERN; 54 mib[1] = KERN_ARND; 55 done = 0; 56 57 do { 58 len = size; 59 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1) 60 return (done); 61 done += len; 62 buf += len; 63 size -= len; 64 } while (size > 0); 65 66 return (done); 67 } 68 69 /* 70 * If a newer libc is accidentally installed on an older kernel, provide high 71 * quality random data anyway. The sysctl interface is not as fast and does 72 * not block by itself, but is provided by even very old kernels. 73 */ 74 static int 75 getentropy_fallback(void *buf, size_t buflen) 76 { 77 /* 78 * oldp (buf) == NULL has a special meaning for sysctl that results in 79 * no EFAULT. For compatibility with the kernel getrandom(2), detect 80 * this case and return the appropriate error. 81 */ 82 if (buf == NULL && buflen > 0) { 83 errno = EFAULT; 84 return (-1); 85 } 86 if (arnd_sysctl(buf, buflen) != buflen) { 87 if (errno == EFAULT) 88 return (-1); 89 /* 90 * This cannot happen. _arc4_sysctl() spins until the random 91 * device is seeded and then repeatedly reads until the full 92 * request is satisfied. The only way for this to return a zero 93 * byte or short read is if sysctl(2) on the kern.arandom MIB 94 * fails. In this case, exceping the user-provided-a-bogus- 95 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir). 96 */ 97 abort(); 98 } 99 return (0); 100 } 101 102 int 103 getentropy(void *buf, size_t buflen) 104 { 105 ssize_t rd; 106 bool have_getrandom; 107 108 if (buflen > 256) { 109 errno = EIO; 110 return (-1); 111 } 112 113 have_getrandom = (__getosreldate() >= GETRANDOM_FIRST); 114 115 while (buflen > 0) { 116 if (have_getrandom) { 117 rd = getrandom(buf, buflen, 0); 118 if (rd == -1) { 119 switch (errno) { 120 case ECAPMODE: 121 /* 122 * Kernel >= r331280 and < r337999 123 * will return ECAPMODE when the 124 * caller is already in capability 125 * mode, fallback to traditional 126 * method in this case. 127 */ 128 have_getrandom = false; 129 continue; 130 case EINTR: 131 continue; 132 default: 133 return (-1); 134 } 135 } 136 } else { 137 return (getentropy_fallback(buf, buflen)); 138 } 139 140 /* This cannot happen. */ 141 if (rd == 0) 142 abort(); 143 144 buf = (char *)buf + rd; 145 buflen -= rd; 146 } 147 148 return (0); 149 } 150