--- /dev/null
+/*
+ * Copyright (C) 2023 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#include <lttng/constant.h>
+
+#include <common/file-descriptor.hpp>
+#include <common/format.hpp>
+#include <common/hashtable/utils.hpp>
+#include <common/random.hpp>
+#include <common/readwrite.hpp>
+#include <common/time.hpp>
+
+#include <fcntl.h>
+
+#ifdef HAVE_SYS_SYSCALL_H
+#include <sys/syscall.h>
+#endif
+
+#define LTTNG_THROW_RANDOM_PRODUCTION_ERROR(msg) \
+ throw lttng::random::production_error(msg, __FILE__, __func__, __LINE__)
+
+namespace {
+/* getrandom is available in Linux >= 3.17. */
+#if defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H)
+
+#include <sys/random.h>
+
+/* A glibc wrapper is provided only for glibc >= 2.25. */
+#if defined(HAVE_GETRANDOM)
+/* Simply use the existing wrapper, passing the non-block flag. */
+ssize_t _call_getrandom_nonblock(char *out_data, std::size_t size)
+{
+ return getrandom(out_data, size, GRND_NONBLOCK);
+}
+#else
+ssize_t _call_getrandom_nonblock(char *out_data, std::size_t size)
+{
+ const int grnd_nonblock_flag = 0x1;
+
+ auto ret = syscall(SYS_getrandom, out_data, size, grnd_nonblock_flag);
+ if (ret < 0) {
+ errno = -ret;
+ ret = -1;
+ }
+
+ return ret;
+}
+#endif /* defined(HAVE_GETRANDOM) */
+
+/* Returns either with a full read or throws. */
+void getrandom_nonblock(char *out_data, std::size_t size)
+{
+ /*
+ * Since GRND_RANDOM is _not_ used, a partial read can only be caused
+ * by a signal interruption. In this case, retry.
+ */
+ ssize_t ret;
+
+ do {
+ ret = _call_getrandom_nonblock(out_data, size);
+ } while ((ret > 0 && ret != size) || (ret == -1 && errno == EINTR));
+
+ if (ret < 0) {
+ LTTNG_THROW_POSIX(
+ fmt::format("Failed to get true random data using getrandom(): size={}",
+ size),
+ errno);
+ }
+}
+#else /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
+void getrandom_nonblock(char *out_data, std::size_t size)
+{
+ LTTNG_THROW_RANDOM_PRODUCTION_ERROR(
+ "getrandom() is not supported by this platform");
+}
+#endif /* defined(__linux__) && defined(SYS_getrandom) && defined(HAVE_SYS_RANDOM_H) */
+
+lttng::random::seed_t produce_pseudo_random_seed()
+{
+ int ret;
+ struct timespec real_time = {};
+ struct timespec monotonic_time = {};
+ unsigned long hash_seed;
+ char hostname[LTTNG_HOST_NAME_MAX] = {};
+ unsigned long seed;
+
+ ret = clock_gettime(CLOCK_REALTIME, &real_time);
+ if (ret) {
+ LTTNG_THROW_POSIX("Failed to read real time while generating pseudo-random seed",
+ errno);
+ }
+
+ ret = clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
+ if (ret) {
+ LTTNG_THROW_POSIX(
+ "Failed to read monotonic time while generating pseudo-random seed",
+ errno);
+ }
+
+ ret = gethostname(hostname, sizeof(hostname));
+ if (ret) {
+ LTTNG_THROW_POSIX("Failed to get host name while generating pseudo-random seed",
+ errno);
+ }
+
+ hash_seed = (unsigned long) real_time.tv_nsec ^ (unsigned long) real_time.tv_sec ^
+ (unsigned long) monotonic_time.tv_nsec ^
+ (unsigned long) monotonic_time.tv_sec;
+ seed = hash_key_ulong((void *) real_time.tv_sec, hash_seed);
+ seed ^= hash_key_ulong((void *) real_time.tv_nsec, hash_seed);
+ seed ^= hash_key_ulong((void *) monotonic_time.tv_sec, hash_seed);
+ seed ^= hash_key_ulong((void *) monotonic_time.tv_nsec, hash_seed);
+
+ const unsigned long pid = getpid();
+ seed ^= hash_key_ulong((void *) pid, hash_seed);
+ seed ^= hash_key_str(hostname, hash_seed);
+
+ return static_cast<lttng::random::seed_t>(seed);
+}
+
+lttng::random::seed_t produce_random_seed_from_urandom()
+{
+ /*
+ * Open /dev/urandom as a file_descriptor, or throw on error. The
+ * lambda is used to reduce the scope of the raw fd as much as possible.
+ */
+ lttng::file_descriptor urandom{[]() {
+ const auto urandom_raw_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
+
+ if (urandom_raw_fd < 0) {
+ LTTNG_THROW_POSIX("Failed to open `/dev/urandom`", errno);
+ }
+
+ return urandom_raw_fd;
+ }()};
+
+ lttng::random::seed_t seed;
+ const auto read_ret = lttng_read(urandom.fd(), &seed, sizeof(seed));
+ if (read_ret != sizeof(seed)) {
+ LTTNG_THROW_POSIX(fmt::format("Failed to read from `/dev/urandom`: size={}",
+ sizeof(seed)),
+ errno);
+ }
+
+ return seed;
+}
+
+} /* namespace */
+
+lttng::random::production_error::production_error(const std::string& msg,
+ const char *file_name,
+ const char *function_name,
+ unsigned int line_number) :
+ lttng::runtime_error(msg, file_name, function_name, line_number)
+{
+}
+
+lttng::random::seed_t lttng::random::produce_true_random_seed()
+{
+ lttng::random::seed_t seed;
+
+ getrandom_nonblock(reinterpret_cast<char *>(&seed), sizeof(seed));
+ return seed;
+}
+
+lttng::random::seed_t lttng::random::produce_best_effort_random_seed()
+{
+ try {
+ return lttng::random::produce_true_random_seed();
+ } catch (std::exception& e) {
+ WARN("%s",
+ 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: {}",
+ e.what())
+ .c_str());
+ }
+
+ try {
+ /*
+ * Can fail for various reasons, including not being accessible
+ * under some containerized environments.
+ */
+ produce_random_seed_from_urandom();
+ } catch (std::exception& e) {
+ WARN("%s",
+ fmt::format("Failed to produce a random seed from the urandom device: {}",
+ e.what())
+ .c_str());
+ }
+
+ /* Fallback to time-based seed generation. */
+ return produce_pseudo_random_seed();
+}
--- /dev/null
+/*
+ * Copyright (C) 2023 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#ifndef LTTNG_RANDOM_H
+#define LTTNG_RANDOM_H
+
+#include "exception.hpp"
+
+#include <cstddef>
+#include <string>
+
+namespace lttng {
+namespace random {
+
+using seed_t = unsigned int;
+
+class production_error : public ::lttng::runtime_error {
+public:
+ explicit production_error(const std::string& msg,
+ const char *file_name,
+ const char *function_name,
+ unsigned int line_number);
+};
+
+/*
+ * Get a seed from a reliable source of randomness without blocking, raising
+ * an exception on failure.
+ */
+seed_t produce_true_random_seed();
+
+/*
+ * Get a random seed making a best-effort to use a true randomness source,
+ * but falling back to a pseudo-random seed based on the time and various system
+ * configuration values on failure.
+ *
+ * Note that this function attempts to use the urandom device, which will block
+ * in the unlikely event that its pool is uninitialized, on platforms that don't
+ * provide getrandom().
+ */
+seed_t produce_best_effort_random_seed();
+
+} /* namespace random */
+} /* namespace lttng */
+
+#endif /* LTTNG_RANDOM_H */
projects / lttng-tools.git / commitdiff
