| 1 | /* |
| 2 | * Copyright (C) 2023 Jérémie Galarneau <jeremie.galarneau@efficios.com> |
| 3 | * |
| 4 | * SPDX-License-Identifier: LGPL-2.1-only |
| 5 | * |
| 6 | */ |
| 7 | |
| 8 | #include <common/error.hpp> |
| 9 | #include <common/file-descriptor.hpp> |
| 10 | #include <common/format.hpp> |
| 11 | #include <common/hashtable/utils.hpp> |
| 12 | #include <common/random.hpp> |
| 13 | #include <common/readwrite.hpp> |
| 14 | #include <common/time.hpp> |
| 15 | |
| 16 | #include <lttng/constant.h> |
| 17 | |
| 18 | #include <fcntl.h> |
| 19 | |
| 20 | #ifdef HAVE_SYS_SYSCALL_H |
| 21 | #include <sys/syscall.h> |
| 22 | #endif |
| 23 | |
| 24 | #define LTTNG_THROW_RANDOM_PRODUCTION_ERROR(msg) \ |
| 25 | throw lttng::random::production_error(msg, __FILE__, __func__, __LINE__) |
| 26 | |
| 27 | namespace { |
| 28 | /* getrandom is available in Linux >= 3.17. */ |
| 29 | #if defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) |
| 30 | |
| 31 | #include <sys/random.h> |
| 32 | |
| 33 | /* A glibc wrapper is provided only for glibc >= 2.25. */ |
| 34 | #if defined(HAVE_GETRANDOM) |
| 35 | /* Simply use the existing wrapper, passing the non-block flag. */ |
| 36 | ssize_t _call_getrandom_nonblock(char *out_data, std::size_t size) |
| 37 | { |
| 38 | return getrandom(out_data, size, GRND_NONBLOCK); |
| 39 | } |
| 40 | #else |
| 41 | ssize_t _call_getrandom_nonblock(char *out_data, std::size_t size) |
| 42 | { |
| 43 | const int grnd_nonblock_flag = 0x1; |
| 44 | |
| 45 | auto ret = syscall(SYS_getrandom, out_data, size, grnd_nonblock_flag); |
| 46 | if (ret < 0) { |
| 47 | errno = -ret; |
| 48 | ret = -1; |
| 49 | } |
| 50 | |
| 51 | return ret; |
| 52 | } |
| 53 | #endif /* defined(HAVE_GETRANDOM) */ |
| 54 | |
| 55 | /* Returns either with a full read or throws. */ |
| 56 | void getrandom_nonblock(char *out_data, std::size_t size) |
| 57 | { |
| 58 | /* |
| 59 | * Since GRND_RANDOM is _not_ used, a partial read can only be caused |
| 60 | * by a signal interruption. In this case, retry. |
| 61 | */ |
| 62 | ssize_t ret; |
| 63 | |
| 64 | do { |
| 65 | ret = _call_getrandom_nonblock(out_data, size); |
| 66 | } while ((ret > 0 && ret != size) || (ret == -1 && errno == EINTR)); |
| 67 | |
| 68 | if (ret < 0) { |
| 69 | LTTNG_THROW_POSIX( |
| 70 | fmt::format("Failed to get true random data using getrandom(): size={}", |
| 71 | size), |
| 72 | errno); |
| 73 | } |
| 74 | } |
| 75 | #else /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */ |
| 76 | __attribute__((noreturn)) void getrandom_nonblock(char *out_data __attribute__((unused)), |
| 77 | std::size_t size __attribute__((unused))) |
| 78 | { |
| 79 | LTTNG_THROW_RANDOM_PRODUCTION_ERROR("getrandom() is not supported by this platform"); |
| 80 | } |
| 81 | #endif /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */ |
| 82 | |
| 83 | lttng::random::seed_t produce_pseudo_random_seed() |
| 84 | { |
| 85 | int ret; |
| 86 | struct timespec real_time = {}; |
| 87 | struct timespec monotonic_time = {}; |
| 88 | unsigned long hash_seed; |
| 89 | char hostname[LTTNG_HOST_NAME_MAX] = {}; |
| 90 | unsigned long seed; |
| 91 | |
| 92 | ret = clock_gettime(CLOCK_REALTIME, &real_time); |
| 93 | if (ret) { |
| 94 | LTTNG_THROW_POSIX("Failed to read real time while generating pseudo-random seed", |
| 95 | errno); |
| 96 | } |
| 97 | |
| 98 | ret = clock_gettime(CLOCK_MONOTONIC, &monotonic_time); |
| 99 | if (ret) { |
| 100 | LTTNG_THROW_POSIX( |
| 101 | "Failed to read monotonic time while generating pseudo-random seed", errno); |
| 102 | } |
| 103 | |
| 104 | ret = gethostname(hostname, sizeof(hostname)); |
| 105 | if (ret) { |
| 106 | LTTNG_THROW_POSIX("Failed to get host name while generating pseudo-random seed", |
| 107 | errno); |
| 108 | } |
| 109 | |
| 110 | hash_seed = (unsigned long) real_time.tv_nsec ^ (unsigned long) real_time.tv_sec ^ |
| 111 | (unsigned long) monotonic_time.tv_nsec ^ (unsigned long) monotonic_time.tv_sec; |
| 112 | seed = hash_key_ulong((void *) real_time.tv_sec, hash_seed); |
| 113 | seed ^= hash_key_ulong((void *) real_time.tv_nsec, hash_seed); |
| 114 | seed ^= hash_key_ulong((void *) monotonic_time.tv_sec, hash_seed); |
| 115 | seed ^= hash_key_ulong((void *) monotonic_time.tv_nsec, hash_seed); |
| 116 | |
| 117 | const unsigned long pid = getpid(); |
| 118 | seed ^= hash_key_ulong((void *) pid, hash_seed); |
| 119 | seed ^= hash_key_str(hostname, hash_seed); |
| 120 | |
| 121 | return static_cast<lttng::random::seed_t>(seed); |
| 122 | } |
| 123 | |
| 124 | lttng::random::seed_t produce_random_seed_from_urandom() |
| 125 | { |
| 126 | /* |
| 127 | * Open /dev/urandom as a file_descriptor, or throw on error. The |
| 128 | * lambda is used to reduce the scope of the raw fd as much as possible. |
| 129 | */ |
| 130 | lttng::file_descriptor urandom{ []() { |
| 131 | const auto urandom_raw_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC); |
| 132 | |
| 133 | if (urandom_raw_fd < 0) { |
| 134 | LTTNG_THROW_POSIX("Failed to open `/dev/urandom`", errno); |
| 135 | } |
| 136 | |
| 137 | return urandom_raw_fd; |
| 138 | }() }; |
| 139 | |
| 140 | lttng::random::seed_t seed; |
| 141 | try { |
| 142 | urandom.read(&seed, sizeof(seed)); |
| 143 | } catch (const std::exception& e) { |
| 144 | LTTNG_THROW_RANDOM_PRODUCTION_ERROR(fmt::format( |
| 145 | "Failed to read from `/dev/urandom`: size={}: {}", sizeof(seed), e.what())); |
| 146 | } |
| 147 | |
| 148 | return seed; |
| 149 | } |
| 150 | |
| 151 | } /* namespace */ |
| 152 | |
| 153 | lttng::random::production_error::production_error(const std::string& msg, |
| 154 | const char *file_name, |
| 155 | const char *function_name, |
| 156 | unsigned int line_number) : |
| 157 | lttng::runtime_error(msg, file_name, function_name, line_number) |
| 158 | { |
| 159 | } |
| 160 | |
| 161 | lttng::random::seed_t lttng::random::produce_true_random_seed() |
| 162 | { |
| 163 | lttng::random::seed_t seed; |
| 164 | |
| 165 | getrandom_nonblock(reinterpret_cast<char *>(&seed), sizeof(seed)); |
| 166 | return seed; |
| 167 | } |
| 168 | |
| 169 | lttng::random::seed_t lttng::random::produce_best_effort_random_seed() |
| 170 | { |
| 171 | try { |
| 172 | return lttng::random::produce_true_random_seed(); |
| 173 | } catch (const std::exception& e) { |
| 174 | WARN("%s", |
| 175 | fmt::format( |
| 176 | "Failed to produce a random seed using getrandom(), falling back to pseudo-random device seed generation which will block until its pool is initialized: {}", |
| 177 | e.what()) |
| 178 | .c_str()); |
| 179 | } |
| 180 | |
| 181 | try { |
| 182 | /* |
| 183 | * Can fail for various reasons, including not being accessible |
| 184 | * under some containerized environments. |
| 185 | */ |
| 186 | produce_random_seed_from_urandom(); |
| 187 | } catch (const std::exception& e) { |
| 188 | WARN("%s", |
| 189 | fmt::format("Failed to produce a random seed from the urandom device: {}", |
| 190 | e.what()) |
| 191 | .c_str()); |
| 192 | } |
| 193 | |
| 194 | /* Fallback to time-based seed generation. */ |
| 195 | return produce_pseudo_random_seed(); |
| 196 | } |