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
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
|
/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */
#include "lib.h"
#include "randgen.h"
#include <unistd.h>
#include <fcntl.h>
#ifdef DEBUG
/* For reproducing tests, fall back onto using a simple deterministic PRNG */
/* Marsaglia's 1999 KISS, de-macro-ified, and with the fixed KISS11 SHR3,
which is clearly what was intended given the "cycle length 2^123" claim. */
static bool kiss_in_use;
static unsigned int kiss_seed;
static uint32_t kiss_z, kiss_w, kiss_jsr, kiss_jcong;
static void
kiss_init(unsigned int seed)
{
i_info("Random numbers are PRNG using kiss, as per DOVECOT_SRAND=%u", seed);
kiss_seed = seed;
kiss_jsr = 0x5eed5eed; /* simply musn't be 0 */
kiss_z = 1 ^ (kiss_w = kiss_jcong = seed); /* w=z=0 is bad, see Rose */
kiss_in_use = TRUE;
}
static unsigned int
kiss_rand(void)
{
kiss_z = 36969 * (kiss_z&65535) + (kiss_z>>16);
kiss_w = 18000 * (kiss_w&65535) + (kiss_w>>16);
kiss_jcong = 69069 * kiss_jcong + 1234567;
kiss_jsr^=(kiss_jsr<<13); /* <<17, >>13 gives cycle length 2^28.2 max */
kiss_jsr^=(kiss_jsr>>17); /* <<13, >>17 gives maximal cycle length */
kiss_jsr^=(kiss_jsr<<5);
return (((kiss_z<<16) + kiss_w) ^ kiss_jcong) + kiss_jsr;
}
int rand_get_last_seed(unsigned int *seed_r)
{
if (!kiss_in_use)
return -1; /* not using a deterministic PRNG, seed is irrelevant */
*seed_r = kiss_seed;
return 0;
}
#endif
/* get randomness from either getrandom, arc4random or /dev/urandom */
#if defined(HAVE_GETRANDOM) && HAVE_DECL_GETRANDOM != 0
# include <sys/random.h>
# define USE_GETRANDOM
static bool getrandom_present = TRUE;
#elif defined(HAVE_ARC4RANDOM)
# if defined(HAVE_LIBBSD)
# include <bsd/stdlib.h>
# endif
# define USE_ARC4RANDOM
#else
static bool getrandom_present = FALSE;
# define USE_RANDOM_DEV
#endif
static int init_refcount = 0;
static int urandom_fd = -1;
#if defined(USE_GETRANDOM) || defined(USE_RANDOM_DEV)
/* Use a small buffer when reading randomness. This is mainly to make small
random reads more efficient, such as i_rand*(). When reading larger amount
of randomness this buffer is bypassed.
There doesn't seem to be a big difference in Linux system CPU usage when
buffer size is above 16 bytes. Double it just to be safe. Avoid it being
too large anyway so we don't unnecessarily waste CPU and memory. */
#define RANDOM_READ_BUFFER_SIZE 32
static unsigned char random_next[RANDOM_READ_BUFFER_SIZE];
static size_t random_next_pos = 0;
static size_t random_next_size = 0;
static void random_open_urandom(void)
{
urandom_fd = open(DEV_URANDOM_PATH, O_RDONLY);
if (urandom_fd == -1) {
if (errno == ENOENT) {
i_fatal("open("DEV_URANDOM_PATH") failed: doesn't exist,"
"currently we require it");
} else {
i_fatal("open("DEV_URANDOM_PATH") failed: %m");
}
}
fd_close_on_exec(urandom_fd, TRUE);
}
static inline int random_read(unsigned char *buf, size_t size)
{
ssize_t ret = 0;
# if defined(USE_GETRANDOM)
if (getrandom_present) {
ret = getrandom(buf, size, 0);
if (ret < 0 && errno == ENOSYS) {
getrandom_present = FALSE;
/* It gets complicated here... While the libc (and its
headers) indicated that getrandom() was available when
we were compiled, the kernel disagreed just now at
runtime. Fall back to reading /dev/urandom. */
random_open_urandom();
}
}
/* this is here to avoid clang complain,
because getrandom_present will be always FALSE
if USE_GETRANDOM is not defined */
if (!getrandom_present)
# endif
ret = read(urandom_fd, buf, size);
if (unlikely(ret <= 0)) {
if (ret == 0) {
i_fatal("read("DEV_URANDOM_PATH") failed: EOF");
} else if (errno != EINTR) {
if (getrandom_present) {
i_fatal("getrandom() failed: %m");
} else {
i_fatal("read("DEV_URANDOM_PATH") failed: %m");
}
}
}
i_assert(ret > 0 || errno == EINTR);
return ret;
}
#endif
void random_fill(void *buf, size_t size)
{
i_assert(init_refcount > 0);
i_assert(size < SSIZE_T_MAX);
#ifdef DEBUG
if (kiss_in_use) {
for (size_t pos = 0; pos < size; pos++)
((unsigned char*)buf)[pos] = kiss_rand();
return;
}
#endif
#if defined(USE_ARC4RANDOM)
arc4random_buf(buf, size);
#else
size_t pos;
ssize_t ret;
for (pos = 0; pos < size; ) {
if (size >= sizeof(random_next) && random_next_size == 0) {
/* Asking for lots of randomness. Read directly to the
destination buffer. */
ret = random_read(PTR_OFFSET(buf, pos), size - pos);
if (ret > -1)
pos += ret;
} else {
/* Asking for a little randomness. Read via a larger
buffer to reduce the number of syscalls. */
if (random_next_size > random_next_pos)
ret = random_next_size - random_next_pos;
else {
random_next_pos = 0;
ret = random_read(random_next,
sizeof(random_next));
random_next_size = ret < 0 ? 0 : ret;
}
if (ret > 0) {
size_t used = I_MIN(size - pos, (size_t)ret);
memcpy(PTR_OFFSET(buf, pos),
random_next + random_next_pos, used);
random_next_pos += used;
pos += used;
}
}
}
#endif /* defined(USE_ARC4RANDOM) */
}
void random_init(void)
{
/* static analyzer seems to require this */
unsigned int seed = 0;
const char *env_seed;
if (init_refcount++ > 0)
return;
env_seed = getenv("DOVECOT_SRAND");
#ifdef DEBUG
if (env_seed != NULL && str_to_uint(env_seed, &seed) >= 0) {
kiss_init(seed);
/* getrandom_present = FALSE; not needed, only used in random_read() */
goto normal_exit;
}
#else
if (env_seed != NULL && *env_seed != '\0')
i_warning("DOVECOT_SRAND is not available in non-debug builds");
#endif /* DEBUG */
#if defined(USE_RANDOM_DEV)
random_open_urandom();
#endif
/* DO NOT REMOVE THIS - It is also
needed to make sure getrandom really works.
*/
random_fill(&seed, sizeof(seed));
#ifdef DEBUG
if (env_seed != NULL) {
if (strcmp(env_seed, "kiss") != 0)
i_fatal("DOVECOT_SRAND not a number or 'kiss'");
kiss_init(seed);
i_close_fd(&urandom_fd);
}
normal_exit:
#endif
srand(seed);
}
void random_deinit(void)
{
if (--init_refcount > 0)
return;
i_close_fd(&urandom_fd);
}
|
