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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 | |
3df3e884 RC |
6 | ***/ |
7 | ||
11c3a366 | 8 | #include <elf.h> |
3df3e884 | 9 | #include <errno.h> |
3df3e884 | 10 | #include <fcntl.h> |
dccca82b | 11 | #include <linux/random.h> |
11c3a366 | 12 | #include <stdbool.h> |
dccca82b | 13 | #include <stdint.h> |
11c3a366 | 14 | #include <stdlib.h> |
dccca82b | 15 | #include <string.h> |
11c3a366 | 16 | #include <sys/time.h> |
11c3a366 | 17 | |
349cc4a5 | 18 | #if HAVE_SYS_AUXV_H |
5224c2c7 ZJS |
19 | # include <sys/auxv.h> |
20 | #endif | |
21 | ||
349cc4a5 | 22 | #if USE_SYS_RANDOM_H |
5224c2c7 ZJS |
23 | # include <sys/random.h> |
24 | #else | |
25 | # include <linux/random.h> | |
a67dab34 | 26 | #endif |
3df3e884 | 27 | |
3ffd4af2 | 28 | #include "fd-util.h" |
c004493c | 29 | #include "io-util.h" |
3ffd4af2 | 30 | #include "missing.h" |
3df3e884 RC |
31 | #include "random-util.h" |
32 | #include "time-util.h" | |
3df3e884 | 33 | |
f0d09059 | 34 | int acquire_random_bytes(void *p, size_t n, bool high_quality_required) { |
3df3e884 RC |
35 | static int have_syscall = -1; |
36 | ||
37 | _cleanup_close_ int fd = -1; | |
f0d09059 | 38 | unsigned already_done = 0; |
7b54715d | 39 | int r; |
3df3e884 | 40 | |
f0d09059 ZJS |
41 | /* Gathers some randomness from the kernel. This call will never block. If |
42 | * high_quality_required, it will always return some data from the kernel, | |
43 | * regardless of whether the random pool is fully initialized or not. | |
44 | * Otherwise, it will return success if at least some random bytes were | |
45 | * successfully acquired, and an error if the kernel has no entropy whatsover | |
46 | * for us. */ | |
3df3e884 | 47 | |
f0d09059 ZJS |
48 | /* Use the getrandom() syscall unless we know we don't have it. */ |
49 | if (have_syscall != 0) { | |
3df3e884 | 50 | r = getrandom(p, n, GRND_NONBLOCK); |
f0d09059 | 51 | if (r > 0) { |
3df3e884 | 52 | have_syscall = true; |
7b54715d | 53 | if ((size_t) r == n) |
f0d09059 ZJS |
54 | return 0; |
55 | if (!high_quality_required) { | |
ed88a900 | 56 | /* Fill in the remaining bytes using pseudorandom values */ |
f0d09059 ZJS |
57 | pseudorandom_bytes((uint8_t*) p + r, n - r); |
58 | return 0; | |
59 | } | |
60 | ||
61 | already_done = r; | |
62 | } else if (errno == ENOSYS) | |
63 | /* We lack the syscall, continue with reading from /dev/urandom. */ | |
64 | have_syscall = false; | |
65 | else if (errno == EAGAIN) { | |
66 | /* The kernel has no entropy whatsoever. Let's remember to | |
67 | * use the syscall the next time again though. | |
68 | * | |
69 | * If high_quality_required is false, return an error so that | |
70 | * random_bytes() can produce some pseudorandom | |
71 | * bytes. Otherwise, fall back to /dev/urandom, which we know | |
72 | * is empty, but the kernel will produce some bytes for us on | |
73 | * a best-effort basis. */ | |
74 | have_syscall = true; | |
75 | ||
76 | if (!high_quality_required) | |
77 | return -ENODATA; | |
3df3e884 | 78 | } else |
f0d09059 | 79 | return -errno; |
3df3e884 RC |
80 | } |
81 | ||
82 | fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); | |
83 | if (fd < 0) | |
84 | return errno == ENOENT ? -ENOSYS : -errno; | |
85 | ||
f0d09059 | 86 | return loop_read_exact(fd, (uint8_t*) p + already_done, n - already_done, true); |
3df3e884 RC |
87 | } |
88 | ||
89 | void initialize_srand(void) { | |
90 | static bool srand_called = false; | |
91 | unsigned x; | |
349cc4a5 | 92 | #if HAVE_SYS_AUXV_H |
3df3e884 RC |
93 | void *auxv; |
94 | #endif | |
95 | ||
96 | if (srand_called) | |
97 | return; | |
98 | ||
349cc4a5 | 99 | #if HAVE_SYS_AUXV_H |
f0d09059 ZJS |
100 | /* The kernel provides us with 16 bytes of entropy in auxv, so let's |
101 | * try to make use of that to seed the pseudo-random generator. It's | |
102 | * better than nothing... */ | |
3df3e884 RC |
103 | |
104 | auxv = (void*) getauxval(AT_RANDOM); | |
ad6b1fa2 | 105 | if (auxv) { |
b5fa4c77 | 106 | assert_cc(sizeof(x) <= 16); |
ad6b1fa2 LP |
107 | memcpy(&x, auxv, sizeof(x)); |
108 | } else | |
3df3e884 | 109 | #endif |
ad6b1fa2 LP |
110 | x = 0; |
111 | ||
3df3e884 RC |
112 | |
113 | x ^= (unsigned) now(CLOCK_REALTIME); | |
114 | x ^= (unsigned) gettid(); | |
115 | ||
116 | srand(x); | |
117 | srand_called = true; | |
118 | } | |
119 | ||
6a06b1a5 ZJS |
120 | /* INT_MAX gives us only 31 bits, so use 24 out of that. */ |
121 | #if RAND_MAX >= INT_MAX | |
122 | # define RAND_STEP 3 | |
123 | #else | |
124 | /* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */ | |
125 | # define RAND_STEP 1 | |
126 | #endif | |
127 | ||
128 | void pseudorandom_bytes(void *p, size_t n) { | |
3df3e884 | 129 | uint8_t *q; |
6a06b1a5 ZJS |
130 | |
131 | initialize_srand(); | |
132 | ||
133 | for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) { | |
134 | unsigned rr; | |
135 | ||
136 | rr = (unsigned) rand(); | |
137 | ||
138 | #if RAND_STEP >= 3 | |
7b54715d | 139 | if ((size_t) (q - (uint8_t*) p + 2) < n) |
6a06b1a5 ZJS |
140 | q[2] = rr >> 16; |
141 | #endif | |
142 | #if RAND_STEP >= 2 | |
7b54715d | 143 | if ((size_t) (q - (uint8_t*) p + 1) < n) |
6a06b1a5 ZJS |
144 | q[1] = rr >> 8; |
145 | #endif | |
146 | q[0] = rr; | |
147 | } | |
148 | } | |
149 | ||
150 | void random_bytes(void *p, size_t n) { | |
3df3e884 RC |
151 | int r; |
152 | ||
f0d09059 | 153 | r = acquire_random_bytes(p, n, false); |
3df3e884 RC |
154 | if (r >= 0) |
155 | return; | |
156 | ||
6a06b1a5 ZJS |
157 | /* If some idiot made /dev/urandom unavailable to us, or the |
158 | * kernel has no entropy, use a PRNG instead. */ | |
159 | return pseudorandom_bytes(p, n); | |
3df3e884 | 160 | } |