src/timesync/timesyncd.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <sys/stat.h>
   4 #include <sys/types.h>
   5
   6 #include "sd-daemon.h"
   7 #include "sd-event.h"
   8 #include "sd-messages.h"
   9
  10 #include "capability-util.h"
  11 #include "clock-util.h"
  12 #include "daemon-util.h"
  13 #include "fd-util.h"
  14 #include "fs-util.h"
  15 #include "main-func.h"
  16 #include "mkdir-label.h"
  17 #include "network-util.h"
  18 #include "process-util.h"
  19 #include "signal-util.h"
  20 #include "timesyncd-bus.h"
  21 #include "timesyncd-conf.h"
  22 #include "timesyncd-manager.h"
  23 #include "user-util.h"
  24
  25 static int advance_tstamp(int fd, const struct stat *st) {
  26         assert_se(fd >= 0);
  27         assert_se(st);
  28
  29         /* So here's the problem: whenever we read the timestamp we'd like to ensure the next time we won't
  30          * restore the exact same time again, but one at least one step further (so that comparing mtimes of
  31          * the timestamp file is a reliable check that timesync did its thing). But file systems have
  32          * different timestamp accuracy: traditional fat has 2s granularity, and even ext2 and friends expose
  33          * different granularity depending on selected inode size during formatting! Hence, to ensure the
  34          * timestamp definitely is increased, here's what we'll do: we'll first try to increase the timestamp
  35          * by 1μs, write that and read it back. If it was updated, great. But if it was not, we'll instead
  36          * increase the timestamp by 10μs, and do the same, then 100μs, then 1ms, and so on, until it works,
  37          * or we reach 10s. If it still didn't work then, the fs is just broken and we give up. */
  38
  39         usec_t target = MAX3(now(CLOCK_REALTIME),
  40                              TIME_EPOCH * USEC_PER_SEC,
  41                              timespec_load(&st->st_mtim));
  42
  43         for (usec_t a = 1; a <= 10 * USEC_PER_SEC; a *= 10) { /* 1μs, 10μs, 100μs, 1ms, … 10s */
  44                 struct timespec ts[2];
  45                 struct stat new_st;
  46
  47                 /* Bump to the maximum of the old timestamp advanced by the specified unit,  */
  48                 usec_t c = usec_add(target, a);
  49
  50                 timespec_store(&ts[0], c);
  51                 ts[1] = ts[0];
  52
  53                 if (futimens(fd, ts) < 0) {
  54                         /* If this doesn't work at all, log, don't fail but give up */
  55                         log_warning_errno(errno, "Unable to update mtime of timestamp file, ignoring: %m");
  56                         return 0;
  57                 }
  58
  59                 if (fstat(fd, &new_st) < 0)
  60                         return log_error_errno(errno, "Failed to stat timestamp file: %m");
  61
  62                 if (timespec_load(&new_st.st_mtim) > target) {
  63                         log_debug("Successfully bumped timestamp file.");
  64                         return 1;
  65                 }
  66
  67                 log_debug("Tried to advance timestamp file by " USEC_FMT ", but this didn't work, file system timestamp granularity too coarse?", a);
  68         }
  69
  70         log_debug("Gave up trying to advance timestamp file.");
  71         return 0;
  72 }
  73
  74 static int load_clock_timestamp(uid_t uid, gid_t gid) {
  75         usec_t min = TIME_EPOCH * USEC_PER_SEC, ct;
  76         _cleanup_close_ int fd = -EBADF;
  77         int r;
  78
  79         /* Let's try to make sure that the clock is always monotonically increasing, by saving the clock
  80          * whenever we have a new NTP time, or when we shut down, and restoring it when we start again. This
  81          * is particularly helpful on systems lacking a battery backed RTC. We also will adjust the time to
  82          * at least the build time of systemd. */
  83
  84         fd = open(CLOCK_FILE, O_RDWR|O_CLOEXEC, 0644);
  85         if (fd < 0) {
  86                 if (errno != ENOENT)
  87                         log_debug_errno(errno, "Unable to open timestamp file '" CLOCK_FILE "', ignoring: %m");
  88
  89                 r = mkdir_safe_label(STATE_DIR, 0755, uid, gid,
  90                                      MKDIR_FOLLOW_SYMLINK | MKDIR_WARN_MODE);
  91                 if (r < 0)
  92                         log_debug_errno(r, "Failed to create state directory, ignoring: %m");
  93
  94                 /* create stamp file with the compiled-in date */
  95                 r = touch_file(CLOCK_FILE, /* parents= */ false, min, uid, gid, 0644);
  96                 if (r < 0)
  97                         log_debug_errno(r, "Failed to create %s, ignoring: %m", CLOCK_FILE);
  98         } else {
  99                 struct stat st;
 100                 usec_t stamp;
 101
 102                 /* check if the recorded time is later than the compiled-in one */
 103                 if (fstat(fd, &st) < 0)
 104                         return log_error_errno(errno, "Unable to stat timestamp file '" CLOCK_FILE "': %m");
 105
 106                 stamp = timespec_load(&st.st_mtim);
 107                 if (stamp > min)
 108                         min = stamp;
 109
 110                 /* Try to fix the access mode, so that we can still touch the file after dropping
 111                  * privileges */
 112                 r = fchmod_and_chown(fd, 0644, uid, gid);
 113                 if (r < 0)
 114                         log_full_errno(ERRNO_IS_PRIVILEGE(r) ? LOG_DEBUG : LOG_WARNING, r,
 115                                        "Failed to chmod or chown %s, ignoring: %m", CLOCK_FILE);
 116
 117                 (void) advance_tstamp(fd, &st);
 118         }
 119
 120         ct = now(CLOCK_REALTIME);
 121         if (ct > min)
 122                 return 0;
 123
 124         /* Not that it matters much, but we actually restore the clock to n+1 here rather than n, simply
 125          * because we read n as time previously already and we want to progress here, i.e. not report the
 126          * same time again. */
 127         if (clock_settime(CLOCK_REALTIME, TIMESPEC_STORE(min+1)) < 0) {
 128                 log_warning_errno(errno, "Failed to restore system clock, ignoring: %m");
 129                 return 0;
 130         }
 131
 132         log_struct(LOG_INFO,
 133                    "MESSAGE_ID=" SD_MESSAGE_TIME_BUMP_STR,
 134                    "REALTIME_USEC=" USEC_FMT, min+1,
 135                    LOG_MESSAGE("System clock time unset or jumped backwards, restored from recorded timestamp: %s",
 136                                FORMAT_TIMESTAMP(min+1)));
 137         return 0;
 138 }
 139
 140 static int run(int argc, char *argv[]) {
 141         _cleanup_(manager_freep) Manager *m = NULL;
 142         _unused_ _cleanup_(notify_on_cleanup) const char *notify_message = NULL;
 143         const char *user = "systemd-timesync";
 144         uid_t uid, uid_current;
 145         gid_t gid;
 146         int r;
 147
 148         log_set_facility(LOG_CRON);
 149         log_setup();
 150
 151         umask(0022);
 152
 153         if (argc != 1)
 154                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "This program does not take arguments.");
 155
 156         uid = uid_current = geteuid();
 157         gid = getegid();
 158
 159         if (uid_current == 0) {
 160                 r = get_user_creds(&user, &uid, &gid, NULL, NULL, 0);
 161                 if (r < 0)
 162                         return log_error_errno(r, "Cannot resolve user name %s: %m", user);
 163         }
 164
 165         r = load_clock_timestamp(uid, gid);
 166         if (r < 0)
 167                 return r;
 168
 169         /* Drop privileges, but only if we have been started as root. If we are not running as root we assume all
 170          * privileges are already dropped. */
 171         if (uid_current == 0) {
 172                 r = drop_privileges(uid, gid, (1ULL << CAP_SYS_TIME));
 173                 if (r < 0)
 174                         return log_error_errno(r, "Failed to drop privileges: %m");
 175         }
 176
 177         assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, SIGRTMIN+18) >= 0);
 178
 179         r = manager_new(&m);
 180         if (r < 0)
 181                 return log_error_errno(r, "Failed to allocate manager: %m");
 182
 183         r = manager_connect_bus(m);
 184         if (r < 0)
 185                 return log_error_errno(r, "Could not connect to bus: %m");
 186
 187         if (clock_is_localtime(NULL) > 0) {
 188                 log_info("The system is configured to read the RTC time in the local time zone. "
 189                          "This mode cannot be fully supported. All system time to RTC updates are disabled.");
 190                 m->rtc_local_time = true;
 191         }
 192
 193         r = manager_parse_config_file(m);
 194         if (r < 0)
 195                 log_warning_errno(r, "Failed to parse configuration file: %m");
 196
 197         r = manager_parse_fallback_string(m, NTP_SERVERS);
 198         if (r < 0)
 199                 return log_error_errno(r, "Failed to parse fallback server strings: %m");
 200
 201         log_debug("systemd-timesyncd running as pid " PID_FMT, getpid_cached());
 202
 203         notify_message = notify_start("READY=1\n"
 204                                       "STATUS=Daemon is running",
 205                                       NOTIFY_STOPPING);
 206
 207         r = manager_setup_save_time_event(m);
 208         if (r < 0)
 209                 return r;
 210
 211         if (network_is_online()) {
 212                 r = manager_connect(m);
 213                 if (r < 0)
 214                         return r;
 215         }
 216
 217         r = sd_event_loop(m->event);
 218         if (r < 0)
 219                 return log_error_errno(r, "Failed to run event loop: %m");
 220
 221         /* if we got an authoritative time, store it in the file system */
 222         if (m->save_on_exit) {
 223                 r = touch(CLOCK_FILE);
 224                 if (r < 0)
 225                         log_debug_errno(r, "Failed to touch " CLOCK_FILE ", ignoring: %m");
 226         }
 227
 228         return 0;
 229 }
 230
 231 DEFINE_MAIN_FUNCTION(run);