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sys_timex: detect clock interference from other processes

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After an ntp_adjtime()/adjtimex() call, check if the frequency, PLL time
constant and PLL status are as expected from the previous call. If they
changed, log a warning message to indicate that another NTP client might
be running on the system and interfering with the system clock.
This commit is contained in:
Miroslav Lichvar
2025-04-03 15:50:29 +02:00
parent d115449e85
commit f7daec0693
1 changed files with 19 additions and 0 deletions
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19
sys_timex.c
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@@ -257,6 +257,8 @@ SYS_Timex_Finalise(void)
int
SYS_Timex_Adjust(struct timex *txc, int ignore_error)
{
static long last_constant, last_freq;
static int last_status = -1;
int state;
#ifdef SOLARIS
@@ -270,7 +272,24 @@ SYS_Timex_Adjust(struct timex *txc, int ignore_error)
if (state < 0) {
LOG(ignore_error ? LOGS_DEBUG : LOGS_FATAL,
NTP_ADJTIME_NAME"(0x%x) failed : %s", txc->modes, strerror(errno));
return state;
}
/* This a good place to verify that nothing else is touching the clock,
without making an additional timex call. A clock update is normally
expected to have four driver calls:
- set_sync_status - primarily updating leap status
- set_frequency - correcting frequency error
- set_frequency - correcting phase error
- set_sync_status - updating leap and estimated/maximum error */
if (last_status != -1 &&
(((last_status ^ txc->status) & STA_PLL && !(txc->modes & MOD_STATUS)) ||
(last_constant != txc->constant && !(txc->modes & MOD_TIMECONST)) ||
(last_freq != txc->freq && !(txc->modes & MOD_FREQUENCY))))
LOG(LOGS_WARN, "System clock interference detected (another NTP client?)");
last_status = txc->status;
last_constant = txc->constant;
last_freq = txc->freq;
return state;
}