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 <common/file-descriptor.hpp>
   9 #include <common/format.hpp>
  10 #include <common/hashtable/utils.hpp>
  11 #include <common/random.hpp>
  12 #include <common/readwrite.hpp>
  13 #include <common/time.hpp>
  14
  15 #include <lttng/constant.h>
  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("getrandom() is not supported by this platform");
  78 }
  79 #endif /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
  80
  81 lttng::random::seed_t produce_pseudo_random_seed()
  82 {
  83         int ret;
  84         struct timespec real_time = {};
  85         struct timespec monotonic_time = {};
  86         unsigned long hash_seed;
  87         char hostname[LTTNG_HOST_NAME_MAX] = {};
  88         unsigned long seed;
  89
  90         ret = clock_gettime(CLOCK_REALTIME, &real_time);
  91         if (ret) {
  92                 LTTNG_THROW_POSIX("Failed to read real time while generating pseudo-random seed",
  93                                   errno);
  94         }
  95
  96         ret = clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
  97         if (ret) {
  98                 LTTNG_THROW_POSIX(
  99                         "Failed to read monotonic time while generating pseudo-random seed", errno);
 100         }
 101
 102         ret = gethostname(hostname, sizeof(hostname));
 103         if (ret) {
 104                 LTTNG_THROW_POSIX("Failed to get host name while generating pseudo-random seed",
 105                                   errno);
 106         }
 107
 108         hash_seed = (unsigned long) real_time.tv_nsec ^ (unsigned long) real_time.tv_sec ^
 109                 (unsigned long) monotonic_time.tv_nsec ^ (unsigned long) monotonic_time.tv_sec;
 110         seed = hash_key_ulong((void *) real_time.tv_sec, hash_seed);
 111         seed ^= hash_key_ulong((void *) real_time.tv_nsec, hash_seed);
 112         seed ^= hash_key_ulong((void *) monotonic_time.tv_sec, hash_seed);
 113         seed ^= hash_key_ulong((void *) monotonic_time.tv_nsec, hash_seed);
 114
 115         const unsigned long pid = getpid();
 116         seed ^= hash_key_ulong((void *) pid, hash_seed);
 117         seed ^= hash_key_str(hostname, hash_seed);
 118
 119         return static_cast<lttng::random::seed_t>(seed);
 120 }
 121
 122 lttng::random::seed_t produce_random_seed_from_urandom()
 123 {
 124         /*
 125          * Open /dev/urandom as a file_descriptor, or throw on error. The
 126          * lambda is used to reduce the scope of the raw fd as much as possible.
 127          */
 128         lttng::file_descriptor urandom{ []() {
 129                 const auto urandom_raw_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
 130
 131                 if (urandom_raw_fd < 0) {
 132                         LTTNG_THROW_POSIX("Failed to open `/dev/urandom`", errno);
 133                 }
 134
 135                 return urandom_raw_fd;
 136         }() };
 137
 138         lttng::random::seed_t seed;
 139         const auto read_ret = lttng_read(urandom.fd(), &seed, sizeof(seed));
 140         if (read_ret != sizeof(seed)) {
 141                 LTTNG_THROW_POSIX(fmt::format("Failed to read from `/dev/urandom`: size={}",
 142                                               sizeof(seed)),
 143                                   errno);
 144         }
 145
 146         return seed;
 147 }
 148
 149 } /* namespace */
 150
 151 lttng::random::production_error::production_error(const std::string& msg,
 152                                                   const char *file_name,
 153                                                   const char *function_name,
 154                                                   unsigned int line_number) :
 155         lttng::runtime_error(msg, file_name, function_name, line_number)
 156 {
 157 }
 158
 159 lttng::random::seed_t lttng::random::produce_true_random_seed()
 160 {
 161         lttng::random::seed_t seed;
 162
 163         getrandom_nonblock(reinterpret_cast<char *>(&seed), sizeof(seed));
 164         return seed;
 165 }
 166
 167 lttng::random::seed_t lttng::random::produce_best_effort_random_seed()
 168 {
 169         try {
 170                 return lttng::random::produce_true_random_seed();
 171         } catch (std::exception& e) {
 172                 WARN("%s",
 173                      fmt::format(
 174                              "Failed to produce a random seed using getrandom(), falling back to pseudo-random device seed generation which will block until its pool is initialized: {}",
 175                              e.what())
 176                              .c_str());
 177         }
 178
 179         try {
 180                 /*
 181                  * Can fail for various reasons, including not being accessible
 182                  * under some containerized environments.
 183                  */
 184                 produce_random_seed_from_urandom();
 185         } catch (std::exception& e) {
 186                 WARN("%s",
 187                      fmt::format("Failed to produce a random seed from the urandom device: {}",
 188                                  e.what())
 189                              .c_str());
 190         }
 191
 192         /* Fallback to time-based seed generation. */
 193         return produce_pseudo_random_seed();
 194 }