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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
3df3e884 RC |
2 | /*** |
3 | This file is part of systemd. | |
4 | ||
5 | Copyright 2010 Lennart Poettering | |
6 | ||
7 | systemd is free software; you can redistribute it and/or modify it | |
8 | under the terms of the GNU Lesser General Public License as published by | |
9 | the Free Software Foundation; either version 2.1 of the License, or | |
10 | (at your option) any later version. | |
11 | ||
12 | systemd is distributed in the hope that it will be useful, but | |
13 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Lesser General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public License | |
18 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
19 | ***/ | |
20 | ||
11c3a366 | 21 | #include <elf.h> |
3df3e884 | 22 | #include <errno.h> |
3df3e884 | 23 | #include <fcntl.h> |
11c3a366 TA |
24 | #include <stdbool.h> |
25 | #include <stdlib.h> | |
26 | #include <sys/time.h> | |
3ffd4af2 LP |
27 | #include <linux/random.h> |
28 | #include <stdint.h> | |
11c3a366 | 29 | |
349cc4a5 | 30 | #if HAVE_SYS_AUXV_H |
5224c2c7 ZJS |
31 | # include <sys/auxv.h> |
32 | #endif | |
33 | ||
349cc4a5 | 34 | #if USE_SYS_RANDOM_H |
5224c2c7 ZJS |
35 | # include <sys/random.h> |
36 | #else | |
37 | # include <linux/random.h> | |
a67dab34 | 38 | #endif |
3df3e884 | 39 | |
3ffd4af2 | 40 | #include "fd-util.h" |
c004493c | 41 | #include "io-util.h" |
3ffd4af2 | 42 | #include "missing.h" |
3df3e884 RC |
43 | #include "random-util.h" |
44 | #include "time-util.h" | |
3df3e884 | 45 | |
f0d09059 | 46 | int acquire_random_bytes(void *p, size_t n, bool high_quality_required) { |
3df3e884 RC |
47 | static int have_syscall = -1; |
48 | ||
49 | _cleanup_close_ int fd = -1; | |
f0d09059 | 50 | unsigned already_done = 0; |
7b54715d | 51 | int r; |
3df3e884 | 52 | |
f0d09059 ZJS |
53 | /* Gathers some randomness from the kernel. This call will never block. If |
54 | * high_quality_required, it will always return some data from the kernel, | |
55 | * regardless of whether the random pool is fully initialized or not. | |
56 | * Otherwise, it will return success if at least some random bytes were | |
57 | * successfully acquired, and an error if the kernel has no entropy whatsover | |
58 | * for us. */ | |
3df3e884 | 59 | |
f0d09059 ZJS |
60 | /* Use the getrandom() syscall unless we know we don't have it. */ |
61 | if (have_syscall != 0) { | |
3df3e884 | 62 | r = getrandom(p, n, GRND_NONBLOCK); |
f0d09059 | 63 | if (r > 0) { |
3df3e884 | 64 | have_syscall = true; |
7b54715d | 65 | if ((size_t) r == n) |
f0d09059 ZJS |
66 | return 0; |
67 | if (!high_quality_required) { | |
ed88a900 | 68 | /* Fill in the remaining bytes using pseudorandom values */ |
f0d09059 ZJS |
69 | pseudorandom_bytes((uint8_t*) p + r, n - r); |
70 | return 0; | |
71 | } | |
72 | ||
73 | already_done = r; | |
74 | } else if (errno == ENOSYS) | |
75 | /* We lack the syscall, continue with reading from /dev/urandom. */ | |
76 | have_syscall = false; | |
77 | else if (errno == EAGAIN) { | |
78 | /* The kernel has no entropy whatsoever. Let's remember to | |
79 | * use the syscall the next time again though. | |
80 | * | |
81 | * If high_quality_required is false, return an error so that | |
82 | * random_bytes() can produce some pseudorandom | |
83 | * bytes. Otherwise, fall back to /dev/urandom, which we know | |
84 | * is empty, but the kernel will produce some bytes for us on | |
85 | * a best-effort basis. */ | |
86 | have_syscall = true; | |
87 | ||
88 | if (!high_quality_required) | |
89 | return -ENODATA; | |
3df3e884 | 90 | } else |
f0d09059 | 91 | return -errno; |
3df3e884 RC |
92 | } |
93 | ||
94 | fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); | |
95 | if (fd < 0) | |
96 | return errno == ENOENT ? -ENOSYS : -errno; | |
97 | ||
f0d09059 | 98 | return loop_read_exact(fd, (uint8_t*) p + already_done, n - already_done, true); |
3df3e884 RC |
99 | } |
100 | ||
101 | void initialize_srand(void) { | |
102 | static bool srand_called = false; | |
103 | unsigned x; | |
349cc4a5 | 104 | #if HAVE_SYS_AUXV_H |
3df3e884 RC |
105 | void *auxv; |
106 | #endif | |
107 | ||
108 | if (srand_called) | |
109 | return; | |
110 | ||
349cc4a5 | 111 | #if HAVE_SYS_AUXV_H |
f0d09059 ZJS |
112 | /* The kernel provides us with 16 bytes of entropy in auxv, so let's |
113 | * try to make use of that to seed the pseudo-random generator. It's | |
114 | * better than nothing... */ | |
3df3e884 RC |
115 | |
116 | auxv = (void*) getauxval(AT_RANDOM); | |
ad6b1fa2 | 117 | if (auxv) { |
b5fa4c77 | 118 | assert_cc(sizeof(x) <= 16); |
ad6b1fa2 LP |
119 | memcpy(&x, auxv, sizeof(x)); |
120 | } else | |
3df3e884 | 121 | #endif |
ad6b1fa2 LP |
122 | x = 0; |
123 | ||
3df3e884 RC |
124 | |
125 | x ^= (unsigned) now(CLOCK_REALTIME); | |
126 | x ^= (unsigned) gettid(); | |
127 | ||
128 | srand(x); | |
129 | srand_called = true; | |
130 | } | |
131 | ||
6a06b1a5 ZJS |
132 | /* INT_MAX gives us only 31 bits, so use 24 out of that. */ |
133 | #if RAND_MAX >= INT_MAX | |
134 | # define RAND_STEP 3 | |
135 | #else | |
136 | /* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */ | |
137 | # define RAND_STEP 1 | |
138 | #endif | |
139 | ||
140 | void pseudorandom_bytes(void *p, size_t n) { | |
3df3e884 | 141 | uint8_t *q; |
6a06b1a5 ZJS |
142 | |
143 | initialize_srand(); | |
144 | ||
145 | for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) { | |
146 | unsigned rr; | |
147 | ||
148 | rr = (unsigned) rand(); | |
149 | ||
150 | #if RAND_STEP >= 3 | |
7b54715d | 151 | if ((size_t) (q - (uint8_t*) p + 2) < n) |
6a06b1a5 ZJS |
152 | q[2] = rr >> 16; |
153 | #endif | |
154 | #if RAND_STEP >= 2 | |
7b54715d | 155 | if ((size_t) (q - (uint8_t*) p + 1) < n) |
6a06b1a5 ZJS |
156 | q[1] = rr >> 8; |
157 | #endif | |
158 | q[0] = rr; | |
159 | } | |
160 | } | |
161 | ||
162 | void random_bytes(void *p, size_t n) { | |
3df3e884 RC |
163 | int r; |
164 | ||
f0d09059 | 165 | r = acquire_random_bytes(p, n, false); |
3df3e884 RC |
166 | if (r >= 0) |
167 | return; | |
168 | ||
6a06b1a5 ZJS |
169 | /* If some idiot made /dev/urandom unavailable to us, or the |
170 | * kernel has no entropy, use a PRNG instead. */ | |
171 | return pseudorandom_bytes(p, n); | |
3df3e884 | 172 | } |