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 <signal.h> 38 #include <stdbool.h> 39 #include <stdlib.h> 40 #include <unistd.h> 41 42 #include "libc_private.h" 43 44 /* First __FreeBSD_version bump after introduction of getrandom(2) (r331279) */ 45 #define GETRANDOM_FIRST 1200061 46 47 extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t); 48 49 static inline void 50 _getentropy_fail(void) 51 { 52 raise(SIGKILL); 53 } 54 55 static size_t 56 arnd_sysctl(u_char *buf, size_t size) 57 { 58 int mib[2]; 59 size_t len, done; 60 61 mib[0] = CTL_KERN; 62 mib[1] = KERN_ARND; 63 done = 0; 64 65 do { 66 len = size; 67 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1) 68 return (done); 69 done += len; 70 buf += len; 71 size -= len; 72 } while (size > 0); 73 74 return (done); 75 } 76 77 /* 78 * If a newer libc is accidentally installed on an older kernel, provide high 79 * quality random data anyway. The sysctl interface is not as fast and does 80 * not block by itself, but is provided by even very old kernels. 81 */ 82 static int 83 getentropy_fallback(void *buf, size_t buflen) 84 { 85 /* 86 * oldp (buf) == NULL has a special meaning for sysctl that results in 87 * no EFAULT. For compatibility with the kernel getrandom(2), detect 88 * this case and return the appropriate error. 89 */ 90 if (buf == NULL && buflen > 0) { 91 errno = EFAULT; 92 return (-1); 93 } 94 if (arnd_sysctl(buf, buflen) != buflen) { 95 if (errno == EFAULT) 96 return (-1); 97 /* 98 * This cannot happen. arnd_sysctl() spins until the random 99 * device is seeded and then repeatedly reads until the full 100 * request is satisfied. The only way for this to return a zero 101 * byte or short read is if sysctl(2) on the kern.arandom MIB 102 * fails. In this case, excepting the user-provided-a-bogus- 103 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir). 104 */ 105 _getentropy_fail(); 106 } 107 return (0); 108 } 109 110 int 111 getentropy(void *buf, size_t buflen) 112 { 113 ssize_t rd; 114 bool have_getrandom; 115 116 if (buflen > 256) { 117 errno = EIO; 118 return (-1); 119 } 120 121 have_getrandom = (__getosreldate() >= GETRANDOM_FIRST); 122 123 while (buflen > 0) { 124 if (have_getrandom) { 125 rd = getrandom(buf, buflen, 0); 126 if (rd == -1) { 127 switch (errno) { 128 case ECAPMODE: 129 /* 130 * Kernel >= r331280 and < r337999 131 * will return ECAPMODE when the 132 * caller is already in capability 133 * mode, fallback to traditional 134 * method in this case. 135 */ 136 have_getrandom = false; 137 continue; 138 case EINTR: 139 continue; 140 case EFAULT: 141 return (-1); 142 default: 143 _getentropy_fail(); 144 } 145 } 146 } else { 147 return (getentropy_fallback(buf, buflen)); 148 } 149 150 /* This cannot happen. */ 151 if (rd == 0) 152 _getentropy_fail(); 153 154 buf = (char *)buf + rd; 155 buflen -= rd; 156 } 157 158 return (0); 159 } 160