src/common/random.cpp

   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 <lttng/constant.h>
   9
  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>
  16
  17 #include <fcntl.h>
  18
  19 #ifdef HAVE_SYS_SYSCALL_H
  20 #include <sys/syscall.h>
  21 #endif
  22
  23 #define LTTNG_THROW_RANDOM_PRODUCTION_ERROR(msg) \
  24         throw lttng::random::production_error(msg, __FILE__, __func__, __LINE__)
  25
  26 namespace {
  27 /* getrandom is available in Linux >= 3.17. */
  28 #if defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H)
  29
  30 #include <sys/random.h>
  31
  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)
  36 {
  37         return getrandom(out_data, size, GRND_NONBLOCK);
  38 }
  39 #else
  40 ssize_t _call_getrandom_nonblock(char *out_data, std::size_t size)
  41 {
  42         const int grnd_nonblock_flag = 0x1;
  43
  44         auto ret = syscall(SYS_getrandom, out_data, size, grnd_nonblock_flag);
  45         if (ret < 0) {
  46                 errno = -ret;
  47                 ret = -1;
  48         }
  49
  50         return ret;
  51 }
  52 #endif /* defined(HAVE_GETRANDOM) */
  53
  54 /* Returns either with a full read or throws. */
  55 void getrandom_nonblock(char *out_data, std::size_t size)
  56 {
  57         /*
  58          * Since GRND_RANDOM is _not_ used, a partial read can only be caused
  59          * by a signal interruption. In this case, retry.
  60          */
  61         ssize_t ret;
  62
  63         do {
  64                 ret = _call_getrandom_nonblock(out_data, size);
  65         } while ((ret > 0 && ret != size) || (ret == -1 && errno == EINTR));
  66
  67         if (ret < 0) {
  68                 LTTNG_THROW_POSIX(
  69                                 fmt::format("Failed to get true random data using getrandom(): size={}",
  70                                                 size),
  71                                 errno);
  72         }
  73 }
  74 #else /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
  75 void getrandom_nonblock(char *out_data, std::size_t size)
  76 {
  77         LTTNG_THROW_RANDOM_PRODUCTION_ERROR(
  78                         "getrandom() is not supported by this platform");
  79 }
  80 #endif /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
  81
  82 lttng::random::seed_t produce_pseudo_random_seed()
  83 {
  84         int ret;
  85         struct timespec real_time = {};
  86         struct timespec monotonic_time = {};
  87         unsigned long hash_seed;
  88         char hostname[LTTNG_HOST_NAME_MAX] = {};
  89         unsigned long seed;
  90
  91         ret = clock_gettime(CLOCK_REALTIME, &real_time);
  92         if (ret) {
  93                 LTTNG_THROW_POSIX("Failed to read real time while generating pseudo-random seed",
  94                                 errno);
  95         }
  96
  97         ret = clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
  98         if (ret) {
  99                 LTTNG_THROW_POSIX(
 100                                 "Failed to read monotonic time while generating pseudo-random seed",
 101                                 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 ^
 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);
 117
 118         const unsigned long pid = getpid();
 119         seed ^= hash_key_ulong((void *) pid, hash_seed);
 120         seed ^= hash_key_str(hostname, hash_seed);
 121
 122         return static_cast<lttng::random::seed_t>(seed);
 123 }
 124
 125 lttng::random::seed_t produce_random_seed_from_urandom()
 126 {
 127         /*
 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.
 130          */
 131         lttng::file_descriptor urandom{[]() {
 132                 const auto urandom_raw_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
 133
 134                 if (urandom_raw_fd < 0) {
 135                         LTTNG_THROW_POSIX("Failed to open `/dev/urandom`", errno);
 136                 }
 137
 138                 return urandom_raw_fd;
 139         }()};
 140
 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={}",
 145                                                   sizeof(seed)),
 146                                 errno);
 147         }
 148
 149         return seed;
 150 }
 151
 152 } /* namespace */
 153
 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)
 159 {
 160 }
 161
 162 lttng::random::seed_t lttng::random::produce_true_random_seed()
 163 {
 164         lttng::random::seed_t seed;
 165
 166         getrandom_nonblock(reinterpret_cast<char *>(&seed), sizeof(seed));
 167         return seed;
 168 }
 169
 170 lttng::random::seed_t lttng::random::produce_best_effort_random_seed()
 171 {
 172         try {
 173                 return lttng::random::produce_true_random_seed();
 174         } catch (std::exception& e) {
 175                 WARN("%s",
 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: {}",
 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 (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 }