2 * Copyright (C) 2023 Jérémie Galarneau <jeremie.galarneau@efficios.com>
4 * SPDX-License-Identifier: LGPL-2.1-only
8 #include <lttng/constant.h>
10 #include <common/file-descriptor.hpp>
11 #include <common/format.hpp>
12 #include <common/hashtable/utils.hpp>
13 #include <common/random.hpp>
14 #include <common/readwrite.hpp>
15 #include <common/time.hpp>
19 #ifdef HAVE_SYS_SYSCALL_H
20 #include <sys/syscall.h>
23 #define LTTNG_THROW_RANDOM_PRODUCTION_ERROR(msg) \
24 throw lttng::random::production_error(msg, __FILE__, __func__, __LINE__)
27 /* getrandom is available in Linux >= 3.17. */
28 #if defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H)
30 #include <sys/random.h>
32 /* A glibc wrapper is provided only for glibc >= 2.25. */
33 #if defined(HAVE_GETRANDOM)
34 /* Simply use the existing wrapper, passing the non-block flag. */
35 ssize_t
_call_getrandom_nonblock(char *out_data
, std::size_t size
)
37 return getrandom(out_data
, size
, GRND_NONBLOCK
);
40 ssize_t
_call_getrandom_nonblock(char *out_data
, std::size_t size
)
42 const int grnd_nonblock_flag
= 0x1;
44 auto ret
= syscall(SYS_getrandom
, out_data
, size
, grnd_nonblock_flag
);
52 #endif /* defined(HAVE_GETRANDOM) */
54 /* Returns either with a full read or throws. */
55 void getrandom_nonblock(char *out_data
, std::size_t size
)
58 * Since GRND_RANDOM is _not_ used, a partial read can only be caused
59 * by a signal interruption. In this case, retry.
64 ret
= _call_getrandom_nonblock(out_data
, size
);
65 } while ((ret
> 0 && ret
!= size
) || (ret
== -1 && errno
== EINTR
));
69 fmt::format("Failed to get true random data using getrandom(): size={}",
74 #else /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
75 void getrandom_nonblock(char *out_data
, std::size_t size
)
77 LTTNG_THROW_RANDOM_PRODUCTION_ERROR(
78 "getrandom() is not supported by this platform");
80 #endif /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
82 lttng::random::seed_t
produce_pseudo_random_seed()
85 struct timespec real_time
= {};
86 struct timespec monotonic_time
= {};
87 unsigned long hash_seed
;
88 char hostname
[LTTNG_HOST_NAME_MAX
] = {};
91 ret
= clock_gettime(CLOCK_REALTIME
, &real_time
);
93 LTTNG_THROW_POSIX("Failed to read real time while generating pseudo-random seed",
97 ret
= clock_gettime(CLOCK_MONOTONIC
, &monotonic_time
);
100 "Failed to read monotonic time while generating pseudo-random seed",
104 ret
= gethostname(hostname
, sizeof(hostname
));
106 LTTNG_THROW_POSIX("Failed to get host name while generating pseudo-random seed",
110 hash_seed
= (unsigned long) real_time
.tv_nsec
^ (unsigned long) real_time
.tv_sec
^
111 (unsigned long) monotonic_time
.tv_nsec
^
112 (unsigned long) monotonic_time
.tv_sec
;
113 seed
= hash_key_ulong((void *) real_time
.tv_sec
, hash_seed
);
114 seed
^= hash_key_ulong((void *) real_time
.tv_nsec
, hash_seed
);
115 seed
^= hash_key_ulong((void *) monotonic_time
.tv_sec
, hash_seed
);
116 seed
^= hash_key_ulong((void *) monotonic_time
.tv_nsec
, hash_seed
);
118 const unsigned long pid
= getpid();
119 seed
^= hash_key_ulong((void *) pid
, hash_seed
);
120 seed
^= hash_key_str(hostname
, hash_seed
);
122 return static_cast<lttng::random::seed_t
>(seed
);
125 lttng::random::seed_t
produce_random_seed_from_urandom()
128 * Open /dev/urandom as a file_descriptor, or throw on error. The
129 * lambda is used to reduce the scope of the raw fd as much as possible.
131 lttng::file_descriptor urandom
{[]() {
132 const auto urandom_raw_fd
= open("/dev/urandom", O_RDONLY
| O_CLOEXEC
);
134 if (urandom_raw_fd
< 0) {
135 LTTNG_THROW_POSIX("Failed to open `/dev/urandom`", errno
);
138 return urandom_raw_fd
;
141 lttng::random::seed_t seed
;
142 const auto read_ret
= lttng_read(urandom
.fd(), &seed
, sizeof(seed
));
143 if (read_ret
!= sizeof(seed
)) {
144 LTTNG_THROW_POSIX(fmt::format("Failed to read from `/dev/urandom`: size={}",
154 lttng::random::production_error::production_error(const std::string
& msg
,
155 const char *file_name
,
156 const char *function_name
,
157 unsigned int line_number
) :
158 lttng::runtime_error(msg
, file_name
, function_name
, line_number
)
162 lttng::random::seed_t
lttng::random::produce_true_random_seed()
164 lttng::random::seed_t seed
;
166 getrandom_nonblock(reinterpret_cast<char *>(&seed
), sizeof(seed
));
170 lttng::random::seed_t
lttng::random::produce_best_effort_random_seed()
173 return lttng::random::produce_true_random_seed();
174 } catch (std::exception
& e
) {
176 fmt::format("Failed to produce a random seed using getrandom(), falling back to pseudo-random device seed generation which will block until its pool is initialized: {}",
183 * Can fail for various reasons, including not being accessible
184 * under some containerized environments.
186 produce_random_seed_from_urandom();
187 } catch (std::exception
& e
) {
189 fmt::format("Failed to produce a random seed from the urandom device: {}",
194 /* Fallback to time-based seed generation. */
195 return produce_pseudo_random_seed();
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