1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 #include <sys/param.h> 31 #include <sys/random.h> 32 #include <sys/sysctl.h> 33 34 #include <errno.h> 35 #include <signal.h> 36 #include <stdbool.h> 37 #include <stdlib.h> 38 #include <unistd.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 inline void 48 _getentropy_fail(void) 49 { 50 raise(SIGKILL); 51 } 52 53 static size_t 54 arnd_sysctl(u_char *buf, size_t size) 55 { 56 int mib[2]; 57 size_t len, done; 58 59 mib[0] = CTL_KERN; 60 mib[1] = KERN_ARND; 61 done = 0; 62 63 do { 64 len = size; 65 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1) 66 return (done); 67 done += len; 68 buf += len; 69 size -= len; 70 } while (size > 0); 71 72 return (done); 73 } 74 75 /* 76 * If a newer libc is accidentally installed on an older kernel, provide high 77 * quality random data anyway. The sysctl interface is not as fast and does 78 * not block by itself, but is provided by even very old kernels. 79 */ 80 static int 81 getentropy_fallback(void *buf, size_t buflen) 82 { 83 /* 84 * oldp (buf) == NULL has a special meaning for sysctl that results in 85 * no EFAULT. For compatibility with the kernel getrandom(2), detect 86 * this case and return the appropriate error. 87 */ 88 if (buf == NULL && buflen > 0) { 89 errno = EFAULT; 90 return (-1); 91 } 92 if (arnd_sysctl(buf, buflen) != buflen) { 93 if (errno == EFAULT) 94 return (-1); 95 /* 96 * This cannot happen. arnd_sysctl() spins until the random 97 * device is seeded and then repeatedly reads until the full 98 * request is satisfied. The only way for this to return a zero 99 * byte or short read is if sysctl(2) on the kern.arandom MIB 100 * fails. In this case, excepting the user-provided-a-bogus- 101 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir). 102 */ 103 _getentropy_fail(); 104 } 105 return (0); 106 } 107 108 int 109 getentropy(void *buf, size_t buflen) 110 { 111 ssize_t rd; 112 bool have_getrandom; 113 114 if (buflen > 256) { 115 errno = EIO; 116 return (-1); 117 } 118 119 have_getrandom = (__getosreldate() >= GETRANDOM_FIRST); 120 121 while (buflen > 0) { 122 if (have_getrandom) { 123 rd = getrandom(buf, buflen, 0); 124 if (rd == -1) { 125 switch (errno) { 126 case ECAPMODE: 127 /* 128 * Kernel >= r331280 and < r337999 129 * will return ECAPMODE when the 130 * caller is already in capability 131 * mode, fallback to traditional 132 * method in this case. 133 */ 134 have_getrandom = false; 135 continue; 136 case EINTR: 137 continue; 138 case EFAULT: 139 return (-1); 140 default: 141 _getentropy_fail(); 142 } 143 } 144 } else { 145 return (getentropy_fallback(buf, buflen)); 146 } 147 148 /* This cannot happen. */ 149 if (rd == 0) 150 _getentropy_fail(); 151 152 buf = (char *)buf + rd; 153 buflen -= rd; 154 } 155 156 return (0); 157 } 158