1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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/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
_getentropy_fail(void)50 _getentropy_fail(void)
51 {
52 raise(SIGKILL);
53 }
54
55 static size_t
arnd_sysctl(u_char * buf,size_t size)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
getentropy_fallback(void * buf,size_t buflen)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
getentropy(void * buf,size_t buflen)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