diff options
Diffstat (limited to 'src/timesync/timesyncd.c')
| -rw-r--r-- | src/timesync/timesyncd.c | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/src/timesync/timesyncd.c b/src/timesync/timesyncd.c new file mode 100644 index 0000000..1d8ebec --- /dev/null +++ b/src/timesync/timesyncd.c @@ -0,0 +1,231 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <sys/stat.h> +#include <sys/types.h> + +#include "sd-daemon.h" +#include "sd-event.h" +#include "sd-messages.h" + +#include "capability-util.h" +#include "clock-util.h" +#include "daemon-util.h" +#include "fd-util.h" +#include "fs-util.h" +#include "main-func.h" +#include "mkdir-label.h" +#include "network-util.h" +#include "process-util.h" +#include "signal-util.h" +#include "timesyncd-bus.h" +#include "timesyncd-conf.h" +#include "timesyncd-manager.h" +#include "user-util.h" + +static int advance_tstamp(int fd, const struct stat *st) { + assert_se(fd >= 0); + assert_se(st); + + /* So here's the problem: whenever we read the timestamp we'd like to ensure the next time we won't + * restore the exact same time again, but one at least one step further (so that comparing mtimes of + * the timestamp file is a reliable check that timesync did its thing). But file systems have + * different timestamp accuracy: traditional fat has 2s granularity, and even ext2 and friends expose + * different granularity depending on selected inode size during formatting! Hence, to ensure the + * timestamp definitely is increased, here's what we'll do: we'll first try to increase the timestamp + * by 1μs, write that and read it back. If it was updated, great. But if it was not, we'll instead + * increase the timestamp by 10μs, and do the same, then 100μs, then 1ms, and so on, until it works, + * or we reach 10s. If it still didn't work then, the fs is just broken and we give up. */ + + usec_t target = MAX3(now(CLOCK_REALTIME), + TIME_EPOCH * USEC_PER_SEC, + timespec_load(&st->st_mtim)); + + for (usec_t a = 1; a <= 10 * USEC_PER_SEC; a *= 10) { /* 1μs, 10μs, 100μs, 1ms, … 10s */ + struct timespec ts[2]; + struct stat new_st; + + /* Bump to the maximum of the old timestamp advanced by the specified unit, */ + usec_t c = usec_add(target, a); + + timespec_store(&ts[0], c); + ts[1] = ts[0]; + + if (futimens(fd, ts) < 0) { + /* If this doesn't work at all, log, don't fail but give up */ + log_warning_errno(errno, "Unable to update mtime of timestamp file, ignoring: %m"); + return 0; + } + + if (fstat(fd, &new_st) < 0) + return log_error_errno(errno, "Failed to stat timestamp file: %m"); + + if (timespec_load(&new_st.st_mtim) > target) { + log_debug("Successfully bumped timestamp file."); + return 1; + } + + log_debug("Tried to advance timestamp file by " USEC_FMT ", but this didn't work, file system timestamp granularity too coarse?", a); + } + + log_debug("Gave up trying to advance timestamp file."); + return 0; +} + +static int load_clock_timestamp(uid_t uid, gid_t gid) { + usec_t min = TIME_EPOCH * USEC_PER_SEC, ct; + _cleanup_close_ int fd = -EBADF; + int r; + + /* Let's try to make sure that the clock is always monotonically increasing, by saving the clock + * whenever we have a new NTP time, or when we shut down, and restoring it when we start again. This + * is particularly helpful on systems lacking a battery backed RTC. We also will adjust the time to + * at least the build time of systemd. */ + + fd = open(CLOCK_FILE, O_RDWR|O_CLOEXEC, 0644); + if (fd < 0) { + if (errno != ENOENT) + log_debug_errno(errno, "Unable to open timestamp file '" CLOCK_FILE "', ignoring: %m"); + + r = mkdir_safe_label(STATE_DIR, 0755, uid, gid, + MKDIR_FOLLOW_SYMLINK | MKDIR_WARN_MODE); + if (r < 0) + log_debug_errno(r, "Failed to create state directory, ignoring: %m"); + + /* create stamp file with the compiled-in date */ + r = touch_file(CLOCK_FILE, /* parents= */ false, min, uid, gid, 0644); + if (r < 0) + log_debug_errno(r, "Failed to create %s, ignoring: %m", CLOCK_FILE); + } else { + struct stat st; + usec_t stamp; + + /* check if the recorded time is later than the compiled-in one */ + if (fstat(fd, &st) < 0) + return log_error_errno(errno, "Unable to stat timestamp file '" CLOCK_FILE "': %m"); + + stamp = timespec_load(&st.st_mtim); + if (stamp > min) + min = stamp; + + /* Try to fix the access mode, so that we can still touch the file after dropping + * privileges */ + r = fchmod_and_chown(fd, 0644, uid, gid); + if (r < 0) + log_full_errno(ERRNO_IS_PRIVILEGE(r) ? LOG_DEBUG : LOG_WARNING, r, + "Failed to chmod or chown %s, ignoring: %m", CLOCK_FILE); + + (void) advance_tstamp(fd, &st); + } + + ct = now(CLOCK_REALTIME); + if (ct > min) + return 0; + + /* Not that it matters much, but we actually restore the clock to n+1 here rather than n, simply + * because we read n as time previously already and we want to progress here, i.e. not report the + * same time again. */ + if (clock_settime(CLOCK_REALTIME, TIMESPEC_STORE(min+1)) < 0) { + log_warning_errno(errno, "Failed to restore system clock, ignoring: %m"); + return 0; + } + + log_struct(LOG_INFO, + "MESSAGE_ID=" SD_MESSAGE_TIME_BUMP_STR, + "REALTIME_USEC=" USEC_FMT, min+1, + LOG_MESSAGE("System clock time unset or jumped backwards, restored from recorded timestamp: %s", + FORMAT_TIMESTAMP(min+1))); + return 0; +} + +static int run(int argc, char *argv[]) { + _cleanup_(manager_freep) Manager *m = NULL; + _unused_ _cleanup_(notify_on_cleanup) const char *notify_message = NULL; + const char *user = "systemd-timesync"; + uid_t uid, uid_current; + gid_t gid; + int r; + + log_set_facility(LOG_CRON); + log_setup(); + + umask(0022); + + if (argc != 1) + return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "This program does not take arguments."); + + uid = uid_current = geteuid(); + gid = getegid(); + + if (uid_current == 0) { + r = get_user_creds(&user, &uid, &gid, NULL, NULL, 0); + if (r < 0) + return log_error_errno(r, "Cannot resolve user name %s: %m", user); + } + + r = load_clock_timestamp(uid, gid); + if (r < 0) + return r; + + /* Drop privileges, but only if we have been started as root. If we are not running as root we assume all + * privileges are already dropped. */ + if (uid_current == 0) { + r = drop_privileges(uid, gid, (1ULL << CAP_SYS_TIME)); + if (r < 0) + return log_error_errno(r, "Failed to drop privileges: %m"); + } + + assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, SIGRTMIN+18, -1) >= 0); + + r = manager_new(&m); + if (r < 0) + return log_error_errno(r, "Failed to allocate manager: %m"); + + r = manager_connect_bus(m); + if (r < 0) + return log_error_errno(r, "Could not connect to bus: %m"); + + if (clock_is_localtime(NULL) > 0) { + log_info("The system is configured to read the RTC time in the local time zone. " + "This mode cannot be fully supported. All system time to RTC updates are disabled."); + m->rtc_local_time = true; + } + + r = manager_parse_config_file(m); + if (r < 0) + log_warning_errno(r, "Failed to parse configuration file: %m"); + + r = manager_parse_fallback_string(m, NTP_SERVERS); + if (r < 0) + return log_error_errno(r, "Failed to parse fallback server strings: %m"); + + log_debug("systemd-timesyncd running as pid " PID_FMT, getpid_cached()); + + notify_message = notify_start("READY=1\n" + "STATUS=Daemon is running", + NOTIFY_STOPPING); + + r = manager_setup_save_time_event(m); + if (r < 0) + return r; + + if (network_is_online()) { + r = manager_connect(m); + if (r < 0) + return r; + } + + r = sd_event_loop(m->event); + if (r < 0) + return log_error_errno(r, "Failed to run event loop: %m"); + + /* if we got an authoritative time, store it in the file system */ + if (m->save_on_exit) { + r = touch(CLOCK_FILE); + if (r < 0) + log_debug_errno(r, "Failed to touch " CLOCK_FILE ", ignoring: %m"); + } + + return 0; +} + +DEFINE_MAIN_FUNCTION(run); |