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/* 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);
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