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Merge pull request #26137 from poettering/timesyncd-touch-file-tweaks

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timesync: some tweaks to saved timestamp file handling
This commit is contained in:
Lennart Poettering
2023-01-21 10:46:54 +01:00
committed by GitHub
parent 8b70155815 1acb4f6157
commit 23fcf34a51
3 changed files with 103 additions and 36 deletions
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catalog/systemd.catalog.in
+9
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@@ -528,6 +528,15 @@ Support: %SUPPORT_URL%
For the first time during the current boot an NTP synchronization has been
acquired and the local system clock adjustment has been initiated.
-- 7db73c8af0d94eeb822ae04323fe6ab6
Subject: Initial clock bump
Defined-By: systemd
Support: %SUPPORT_URL%
The system clock has been advanced based on a timestamp file on disk, in order
to ensure it remains roughly monotonic – even across reboots – if an RTC is not
available or is unreliable.
-- 3f7d5ef3e54f4302b4f0b143bb270cab
Subject: TPM PCR Extended
Defined-By: systemd
src/systemd/sd-messages.h
+3
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@@ -183,6 +183,9 @@ _SD_BEGIN_DECLARATIONS;
#define SD_MESSAGE_TIME_SYNC SD_ID128_MAKE(7c,8a,41,f3,7b,76,49,41,a0,e1,78,0b,1b,e2,f0,37)
#define SD_MESSAGE_TIME_SYNC_STR SD_ID128_MAKE_STR(7c,8a,41,f3,7b,76,49,41,a0,e1,78,0b,1b,e2,f0,37)
#define SD_MESSAGE_TIME_BUMP SD_ID128_MAKE(7d,b7,3c,8a,f0,d9,4e,eb,82,2a,e0,43,23,fe,6a,b6)
#define SD_MESSAGE_TIME_BUMP_STR SD_ID128_MAKE_STR(7d,b7,3c,8a,f0,d9,4e,eb,82,2a,e0,43,23,fe,6a,b6)
#define SD_MESSAGE_SHUTDOWN_SCHEDULED SD_ID128_MAKE(9e,70,66,27,9d,c8,40,3d,a7,9c,e4,b1,a6,90,64,b2)
#define SD_MESSAGE_SHUTDOWN_SCHEDULED_STR SD_ID128_MAKE_STR(9e,70,66,27,9d,c8,40,3d,a7,9c,e4,b1,a6,90,64,b2)
src/timesync/timesyncd.c
+91 -36
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@@ -5,6 +5,7 @@
#include "sd-daemon.h"
#include "sd-event.h"
#include "sd-messages.h"
#include "capability-util.h"
#include "clock-util.h"
@@ -21,64 +22,118 @@
#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. */
/* 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) {
struct stat st;
usec_t stamp;
if (fd < 0) {
if (errno != ENOENT)
log_debug_errno(errno, "Unable to open timestamp file '" CLOCK_FILE "', ignoring: %m");
/* check if the recorded time is later than the compiled-in one */
if (fstat(fd, &st) >= 0) {
stamp = timespec_load(&st.st_mtim);
if (stamp > min)
min = stamp;
}
if (geteuid() == 0) {
/* 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_warning_errno(r, "Failed to chmod or chown %s, ignoring: %m", CLOCK_FILE);
}
} else {
r = mkdir_safe_label(STATE_DIR, 0755, uid, gid,
MKDIR_FOLLOW_SYMLINK | MKDIR_WARN_MODE);
if (r < 0) {
if (r < 0)
log_debug_errno(r, "Failed to create state directory, ignoring: %m");
goto settime;
}
/* 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);
}
settime:
ct = now(CLOCK_REALTIME);
if (ct < min) {
char date[FORMAT_TIMESTAMP_MAX];
if (ct > min)
return 0;
log_info("System clock time unset or jumped backwards, restoring from recorded timestamp: %s",
format_timestamp(date, sizeof(date), min));
if (clock_settime(CLOCK_REALTIME, TIMESPEC_STORE(min)) < 0)
log_error_errno(errno, "Failed to restore system clock, ignoring: %m");
/* 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;
}