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/param.h> 30 #include <sys/random.h> 31 #include <sys/sysctl.h> 32 33 #include <errno.h> 34 #include <signal.h> 35 #include <stdbool.h> 36 #include <stdlib.h> 37 #include <unistd.h> 38 39 #include "libc_private.h" 40 41 /* First __FreeBSD_version bump after introduction of getrandom(2) (r331279) */ 42 #define GETRANDOM_FIRST 1200061 43 44 extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t); 45 46 static inline void 47 _getentropy_fail(void) 48 { 49 raise(SIGKILL); 50 } 51 52 static size_t 53 arnd_sysctl(u_char *buf, size_t size) 54 { 55 int mib[2]; 56 size_t len, done; 57 58 mib[0] = CTL_KERN; 59 mib[1] = KERN_ARND; 60 done = 0; 61 62 do { 63 len = size; 64 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1) 65 return (done); 66 done += len; 67 buf += len; 68 size -= len; 69 } while (size > 0); 70 71 return (done); 72 } 73 74 /* 75 * If a newer libc is accidentally installed on an older kernel, provide high 76 * quality random data anyway. The sysctl interface is not as fast and does 77 * not block by itself, but is provided by even very old kernels. 78 */ 79 static int 80 getentropy_fallback(void *buf, size_t buflen) 81 { 82 /* 83 * oldp (buf) == NULL has a special meaning for sysctl that results in 84 * no EFAULT. For compatibility with the kernel getrandom(2), detect 85 * this case and return the appropriate error. 86 */ 87 if (buf == NULL && buflen > 0) { 88 errno = EFAULT; 89 return (-1); 90 } 91 if (arnd_sysctl(buf, buflen) != buflen) { 92 if (errno == EFAULT) 93 return (-1); 94 /* 95 * This cannot happen. arnd_sysctl() spins until the random 96 * device is seeded and then repeatedly reads until the full 97 * request is satisfied. The only way for this to return a zero 98 * byte or short read is if sysctl(2) on the kern.arandom MIB 99 * fails. In this case, excepting the user-provided-a-bogus- 100 * buffer EFAULT, give up (like for arc4random(3)'s arc4_stir). 101 */ 102 _getentropy_fail(); 103 } 104 return (0); 105 } 106 107 int 108 getentropy(void *buf, size_t buflen) 109 { 110 ssize_t rd; 111 bool have_getrandom; 112 113 if (buflen > 256) { 114 errno = EIO; 115 return (-1); 116 } 117 118 have_getrandom = (__getosreldate() >= GETRANDOM_FIRST); 119 120 while (buflen > 0) { 121 if (have_getrandom) { 122 rd = getrandom(buf, buflen, 0); 123 if (rd == -1) { 124 switch (errno) { 125 case ECAPMODE: 126 /* 127 * Kernel >= r331280 and < r337999 128 * will return ECAPMODE when the 129 * caller is already in capability 130 * mode, fallback to traditional 131 * method in this case. 132 */ 133 have_getrandom = false; 134 continue; 135 case EINTR: 136 continue; 137 case EFAULT: 138 return (-1); 139 default: 140 _getentropy_fail(); 141 } 142 } 143 } else { 144 return (getentropy_fallback(buf, buflen)); 145 } 146 147 /* This cannot happen. */ 148 if (rd == 0) 149 _getentropy_fail(); 150 151 buf = (char *)buf + rd; 152 buflen -= rd; 153 } 154 155 return (0); 156 } 157