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3df3e884 RC |
1 | /*** |
2 | This file is part of systemd. | |
3 | ||
4 | Copyright 2010 Lennart Poettering | |
5 | ||
6 | systemd is free software; you can redistribute it and/or modify it | |
7 | under the terms of the GNU Lesser General Public License as published by | |
8 | the Free Software Foundation; either version 2.1 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | systemd is distributed in the hope that it will be useful, but | |
12 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | Lesser General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU Lesser General Public License | |
17 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
18 | ***/ | |
19 | ||
20 | #include <stdint.h> | |
21 | #include <errno.h> | |
22 | #include <sys/types.h> | |
23 | #include <sys/stat.h> | |
24 | #include <fcntl.h> | |
25 | #include <time.h> | |
26 | #include <sys/auxv.h> | |
27 | #include <linux/random.h> | |
28 | ||
29 | #include "random-util.h" | |
30 | #include "time-util.h" | |
31 | #include "missing.h" | |
32 | #include "util.h" | |
33 | ||
34 | int dev_urandom(void *p, size_t n) { | |
35 | static int have_syscall = -1; | |
36 | ||
37 | _cleanup_close_ int fd = -1; | |
38 | int r; | |
39 | ||
40 | /* Gathers some randomness from the kernel. This call will | |
41 | * never block, and will always return some data from the | |
42 | * kernel, regardless if the random pool is fully initialized | |
43 | * or not. It thus makes no guarantee for the quality of the | |
44 | * returned entropy, but is good enough for or usual usecases | |
45 | * of seeding the hash functions for hashtable */ | |
46 | ||
47 | /* Use the getrandom() syscall unless we know we don't have | |
48 | * it, or when the requested size is too large for it. */ | |
49 | if (have_syscall != 0 || (size_t) (int) n != n) { | |
50 | r = getrandom(p, n, GRND_NONBLOCK); | |
51 | if (r == (int) n) { | |
52 | have_syscall = true; | |
53 | return 0; | |
54 | } | |
55 | ||
56 | if (r < 0) { | |
57 | if (errno == ENOSYS) | |
58 | /* we lack the syscall, continue with | |
59 | * reading from /dev/urandom */ | |
60 | have_syscall = false; | |
61 | else if (errno == EAGAIN) | |
62 | /* not enough entropy for now. Let's | |
63 | * remember to use the syscall the | |
64 | * next time, again, but also read | |
65 | * from /dev/urandom for now, which | |
66 | * doesn't care about the current | |
67 | * amount of entropy. */ | |
68 | have_syscall = true; | |
69 | else | |
70 | return -errno; | |
71 | } else | |
72 | /* too short read? */ | |
73 | return -ENODATA; | |
74 | } | |
75 | ||
76 | fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); | |
77 | if (fd < 0) | |
78 | return errno == ENOENT ? -ENOSYS : -errno; | |
79 | ||
80 | return loop_read_exact(fd, p, n, true); | |
81 | } | |
82 | ||
83 | void initialize_srand(void) { | |
84 | static bool srand_called = false; | |
85 | unsigned x; | |
86 | #ifdef HAVE_SYS_AUXV_H | |
87 | void *auxv; | |
88 | #endif | |
89 | ||
90 | if (srand_called) | |
91 | return; | |
92 | ||
93 | x = 0; | |
94 | ||
95 | #ifdef HAVE_SYS_AUXV_H | |
96 | /* The kernel provides us with a bit of entropy in auxv, so | |
97 | * let's try to make use of that to seed the pseudo-random | |
98 | * generator. It's better than nothing... */ | |
99 | ||
100 | auxv = (void*) getauxval(AT_RANDOM); | |
101 | if (auxv) | |
102 | x ^= *(unsigned*) auxv; | |
103 | #endif | |
104 | ||
105 | x ^= (unsigned) now(CLOCK_REALTIME); | |
106 | x ^= (unsigned) gettid(); | |
107 | ||
108 | srand(x); | |
109 | srand_called = true; | |
110 | } | |
111 | ||
112 | void random_bytes(void *p, size_t n) { | |
113 | uint8_t *q; | |
114 | int r; | |
115 | ||
116 | r = dev_urandom(p, n); | |
117 | if (r >= 0) | |
118 | return; | |
119 | ||
120 | /* If some idiot made /dev/urandom unavailable to us, he'll | |
121 | * get a PRNG instead. */ | |
122 | ||
123 | initialize_srand(); | |
124 | ||
125 | for (q = p; q < (uint8_t*) p + n; q ++) | |
126 | *q = rand(); | |
127 | } |