1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2018 Conrad Meyer <[email protected]>
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
_getentropy_fail(void)47 _getentropy_fail(void)
48 {
49 raise(SIGKILL);
50 }
51
52 static size_t
arnd_sysctl(u_char * buf,size_t size)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
getentropy_fallback(void * buf,size_t buflen)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
getentropy(void * buf,size_t buflen)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