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reference: randomize reference time

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In unauthenticated interleaved symmetric NTP mode we should be now
careful with the reference timestamp as it may be useful with the peer
delay for estimating the local receive timestamp and increasing the
chance of spoofing a valid response from the peer.

When updating the reference time, add a random error of up to one second
to make it less sensitive when disclosed to NTP and cmdmon clients.
This commit is contained in:
Miroslav Lichvar 2016-11-23 14:03:12 +01:00
parent 4d7eb2f7a6
commit d75f6830f1
1 changed files with 11 additions and 1 deletions
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12
reference.c
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@ -52,7 +52,7 @@ static int our_leap_sec;
static int our_stratum;
static uint32_t our_ref_id;
static IPAddr our_ref_ip;
struct timespec our_ref_time;
static struct timespec our_ref_time;
static double our_skew;
static double our_residual_freq;
static double our_root_delay;
@ -901,6 +901,7 @@ REF_SetReference(int stratum,
double correction_rate;
double uncorrected_offset, accumulate_offset, step_offset;
struct timespec now, raw_now;
NTP_int64 ref_fuzz;
assert(initialised);
@ -1041,6 +1042,15 @@ REF_SetReference(int stratum,
LCL_SetSyncStatus(are_we_synchronised, offset_sd, offset_sd + root_delay / 2.0 + root_dispersion);
/* Add a random error of up to one second to the reference time to make it
less useful when disclosed to NTP and cmdmon clients for estimating
receive timestamps in the interleaved symmetric NTP mode */
UTI_GetNtp64Fuzz(&ref_fuzz, 0);
UTI_TimespecToNtp64(&our_ref_time, &ref_fuzz, &ref_fuzz);
UTI_Ntp64ToTimespec(&ref_fuzz, &our_ref_time);
if (UTI_CompareTimespecs(&our_ref_time, ref_time) >= 0)
our_ref_time.tv_sec--;
abs_freq_ppm = LCL_ReadAbsoluteFrequency();
write_log(&now,