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ntp: respond to NTPv1 client requests with zero mode

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NTPv1 packets have a reserved field instead of the mode field and the
actual mode is determined from the port numbers. It seems there is still
a large number of clients sending NTPv1 requests with a zero value in
the field (per RFC 1059).

Follow ntpd and respond to the requests with server mode packets.
This commit is contained in:
Miroslav Lichvar 2018-03-07 11:12:52 +01:00
parent 448ef779c2
commit fbca570d0b
1 changed files with 12 additions and 2 deletions
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14
ntp_core.c
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@ -2053,7 +2053,7 @@ NCR_ProcessRxUnknown(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_a
NTP_Mode pkt_mode, my_mode;
NTP_int64 *local_ntp_rx, *local_ntp_tx;
NTP_Local_Timestamp local_tx, *tx_ts;
int valid_auth, log_index, interleaved, poll;
int pkt_version, valid_auth, log_index, interleaved, poll;
AuthenticationMode auth_mode;
uint32_t key_id;
@ -2074,6 +2074,7 @@ NCR_ProcessRxUnknown(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_a
}
pkt_mode = NTP_LVM_TO_MODE(message->lvm);
pkt_version = NTP_LVM_TO_VERSION(message->lvm);
switch (pkt_mode) {
case MODE_ACTIVE:
@ -2084,6 +2085,15 @@ NCR_ProcessRxUnknown(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_a
/* Reply with server packet */
my_mode = MODE_SERVER;
break;
case MODE_UNDEFINED:
/* Check if it is an NTPv1 client request (NTPv1 packets have a reserved
field instead of the mode field and the actual mode is determined from
the port numbers). Don't ever respond with a mode 0 packet! */
if (pkt_version == 1 && remote_addr->port != NTP_PORT) {
my_mode = MODE_SERVER;
break;
}
/* Fall through */
default:
/* Discard */
DEBUG_LOG("NTP packet discarded pkt_mode=%d", pkt_mode);
@ -2147,7 +2157,7 @@ NCR_ProcessRxUnknown(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_a
poll = MAX(poll, message->poll);
/* Send a reply */
transmit_packet(my_mode, interleaved, poll, NTP_LVM_TO_VERSION(message->lvm),
transmit_packet(my_mode, interleaved, poll, pkt_version,
auth_mode, key_id, &message->receive_ts, &message->transmit_ts,
rx_ts, tx_ts, local_ntp_rx, NULL, remote_addr, local_addr);