1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
/* SPDX-License-Identifier: LGPL-2.1+ */
/***
This file is part of systemd.
Copyright 2010 Lennart Poettering
***/
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
//#include <linux/random.h>
#include <stdbool.h>
//#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#if HAVE_SYS_AUXV_H
# include <sys/auxv.h>
#endif
#if USE_SYS_RANDOM_H
# include <sys/random.h>
#else
# include <linux/random.h>
#endif
#include "fd-util.h"
#include "io-util.h"
#include "missing.h"
#include "random-util.h"
#include "time-util.h"
int acquire_random_bytes(void *p, size_t n, bool high_quality_required) {
static int have_syscall = -1;
_cleanup_close_ int fd = -1;
unsigned already_done = 0;
int r;
/* Gathers some randomness from the kernel. This call will never block. If
* high_quality_required, it will always return some data from the kernel,
* regardless of whether the random pool is fully initialized or not.
* Otherwise, it will return success if at least some random bytes were
* successfully acquired, and an error if the kernel has no entropy whatsover
* for us. */
/* Use the getrandom() syscall unless we know we don't have it. */
if (have_syscall != 0) {
r = getrandom(p, n, GRND_NONBLOCK);
if (r > 0) {
have_syscall = true;
if ((size_t) r == n)
return 0;
if (!high_quality_required) {
/* Fill in the remaining bytes using pseudorandom values */
pseudorandom_bytes((uint8_t*) p + r, n - r);
return 0;
}
already_done = r;
} else if (errno == ENOSYS)
/* We lack the syscall, continue with reading from /dev/urandom. */
have_syscall = false;
else if (errno == EAGAIN) {
/* The kernel has no entropy whatsoever. Let's remember to
* use the syscall the next time again though.
*
* If high_quality_required is false, return an error so that
* random_bytes() can produce some pseudorandom
* bytes. Otherwise, fall back to /dev/urandom, which we know
* is empty, but the kernel will produce some bytes for us on
* a best-effort basis. */
have_syscall = true;
if (!high_quality_required)
return -ENODATA;
} else
return -errno;
}
fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (fd < 0)
return errno == ENOENT ? -ENOSYS : -errno;
return loop_read_exact(fd, (uint8_t*) p + already_done, n - already_done, true);
}
void initialize_srand(void) {
static bool srand_called = false;
unsigned x;
#if HAVE_SYS_AUXV_H
void *auxv;
#endif
if (srand_called)
return;
#if HAVE_SYS_AUXV_H
/* The kernel provides us with 16 bytes of entropy in auxv, so let's
* try to make use of that to seed the pseudo-random generator. It's
* better than nothing... */
auxv = (void*) getauxval(AT_RANDOM);
if (auxv) {
assert_cc(sizeof(x) <= 16);
memcpy(&x, auxv, sizeof(x));
} else
#endif
x = 0;
x ^= (unsigned) now(CLOCK_REALTIME);
x ^= (unsigned) gettid();
srand(x);
srand_called = true;
}
/* INT_MAX gives us only 31 bits, so use 24 out of that. */
#if RAND_MAX >= INT_MAX
# define RAND_STEP 3
#else
/* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */
# define RAND_STEP 1
#endif
void pseudorandom_bytes(void *p, size_t n) {
uint8_t *q;
initialize_srand();
for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) {
unsigned rr;
rr = (unsigned) rand();
#if RAND_STEP >= 3
if ((size_t) (q - (uint8_t*) p + 2) < n)
q[2] = rr >> 16;
#endif
#if RAND_STEP >= 2
if ((size_t) (q - (uint8_t*) p + 1) < n)
q[1] = rr >> 8;
#endif
q[0] = rr;
}
}
void random_bytes(void *p, size_t n) {
int r;
r = acquire_random_bytes(p, n, false);
if (r >= 0)
return;
/* If some idiot made /dev/urandom unavailable to us, or the
* kernel has no entropy, use a PRNG instead. */
return pseudorandom_bytes(p, n);
}
|
