faraphel/chrony
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

ntp: don't send packets with RX equal to TX

Browse source 
Before sending an NTP packet, check whether the TX timestamp is not
equal to the RX timestamp. If it is, generate a new TX timestamp and try
again. This is extremely unlikely to happen in normal operation, but it
is needed for reliable detection of the interleaved mode.
This commit is contained in:
Miroslav Lichvar 2017-01-10 11:30:52 +01:00
parent f2f834e7e7
commit 061579ec28
1 changed files with 49 additions and 43 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

92
ntp_core.c
View file

@ -956,57 +956,63 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
frequency all along */
UTI_TimespecToNtp64(&local_receive, &message.receive_ts, &ts_fuzz);
/* Prepare random bits which will be added to the transmit timestamp. */
UTI_GetNtp64Fuzz(&ts_fuzz, precision);
do {
/* Prepare random bits which will be added to the transmit timestamp */
UTI_GetNtp64Fuzz(&ts_fuzz, precision);
/* Transmit - this our local time right now! Also, we might need to
store this for our own use later, next time we receive a message
from the source we're sending to now. */
LCL_ReadCookedTime(&local_transmit, &local_transmit_err);
/* Transmit - this our local time right now! Also, we might need to
store this for our own use later, next time we receive a message
from the source we're sending to now. */
LCL_ReadCookedTime(&local_transmit, &local_transmit_err);
if (smooth_time)
UTI_AddDoubleToTimespec(&local_transmit, smooth_offset, &local_transmit);
if (smooth_time)
UTI_AddDoubleToTimespec(&local_transmit, smooth_offset, &local_transmit);
length = NTP_NORMAL_PACKET_LENGTH;
length = NTP_NORMAL_PACKET_LENGTH;
/* Authenticate the packet if needed */
/* Authenticate the packet */
if (auth_mode == AUTH_SYMMETRIC || auth_mode == AUTH_MSSNTP) {
/* Pre-compensate the transmit time by approx. how long it will
take to generate the authentication data. */
local_transmit.tv_nsec += auth_mode == AUTH_SYMMETRIC ?
KEY_GetAuthDelay(key_id) : NSD_GetAuthDelay(key_id);
UTI_NormaliseTimespec(&local_transmit);
UTI_TimespecToNtp64(interleaved ? &local_tx->ts : &local_transmit,
&message.transmit_ts, &ts_fuzz);
if (auth_mode == AUTH_SYMMETRIC || auth_mode == AUTH_MSSNTP) {
/* Pre-compensate the transmit time by approximately how long it will
take to generate the authentication data */
local_transmit.tv_nsec += auth_mode == AUTH_SYMMETRIC ?
KEY_GetAuthDelay(key_id) : NSD_GetAuthDelay(key_id);
UTI_NormaliseTimespec(&local_transmit);
UTI_TimespecToNtp64(interleaved ? &local_tx->ts : &local_transmit,
&message.transmit_ts, &ts_fuzz);
if (auth_mode == AUTH_SYMMETRIC) {
auth_len = KEY_GenerateAuth(key_id, (unsigned char *) &message,
offsetof(NTP_Packet, auth_keyid),
(unsigned char *)&message.auth_data,
sizeof (message.auth_data));
if (!auth_len) {
DEBUG_LOG(LOGF_NtpCore, "Could not generate auth data with key %"PRIu32, key_id);
return 0;
if (auth_mode == AUTH_SYMMETRIC) {
auth_len = KEY_GenerateAuth(key_id, (unsigned char *) &message,
offsetof(NTP_Packet, auth_keyid),
(unsigned char *)&message.auth_data,
sizeof (message.auth_data));
if (!auth_len) {
DEBUG_LOG(LOGF_NtpCore, "Could not generate auth data with key %"PRIu32, key_id);
return 0;
}
message.auth_keyid = htonl(key_id);
mac_len = sizeof (message.auth_keyid) + auth_len;
/* Truncate MACs in NTPv4 packets to allow deterministic parsing
of extension fields (RFC 7822) */
if (version == 4 && mac_len > NTP_MAX_V4_MAC_LENGTH)
mac_len = NTP_MAX_V4_MAC_LENGTH;
length += mac_len;
} else if (auth_mode == AUTH_MSSNTP) {
/* MS-SNTP packets are signed (asynchronously) by ntp_signd */
return NSD_SignAndSendPacket(key_id, &message, where_to, from, length);
}
message.auth_keyid = htonl(key_id);
mac_len = sizeof (message.auth_keyid) + auth_len;
/* Truncate MACs in NTPv4 packets to allow deterministic parsing
of extension fields (RFC 7822) */
if (version == 4 && mac_len > NTP_MAX_V4_MAC_LENGTH)
mac_len = NTP_MAX_V4_MAC_LENGTH;
length += mac_len;
} else if (auth_mode == AUTH_MSSNTP) {
/* MS-SNTP packets are signed (asynchronously) by ntp_signd */
return NSD_SignAndSendPacket(key_id, &message, where_to, from, length);
} else {
UTI_TimespecToNtp64(interleaved ? &local_tx->ts : &local_transmit,
&message.transmit_ts, &ts_fuzz);
}
} else {
UTI_TimespecToNtp64(interleaved ? &local_tx->ts : &local_transmit,
&message.transmit_ts, &ts_fuzz);
}
/* Avoid sending messages with non-zero transmit timestamp equal to the
receive timestamp to allow reliable detection of the interleaved mode */
} while (!UTI_CompareNtp64(&message.transmit_ts, &message.receive_ts) &&
!UTI_IsZeroNtp64(&message.transmit_ts));
ret = NIO_SendPacket(&message, where_to, from, length, local_tx != NULL);