ntp: move authentication calls in transmit_packet()

Move the calls resetting and generating authentication data out of the
loop checking for unique TX timestamp. This allows the timestamps to be
manipulated after the check.

ntp_core.c

@@ -1054,10 +1054,10 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
     UTI_ZeroNtp64(&message.receive_ts);
   }
 
-  do {
   if (!parse_packet(&message, NTP_HEADER_LENGTH, &info))
     return 0;
 
+  do {
     /* Prepare random bits which will be added to the transmit timestamp */
     UTI_GetNtp64Fuzz(&ts_fuzz, precision);
 
@@ -1072,6 +1072,17 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
     UTI_TimespecToNtp64(interleaved ? &local_tx->ts : &local_transmit,
                         &message.transmit_ts, &ts_fuzz);
 
+    /* Do not send a packet with a non-zero transmit timestamp which is
+       equal to any of the following timestamps:
+       - receive (to allow reliable detection of the interleaved mode)
+       - originate (to prevent the packet from being its own valid response
+                    in the symmetric mode)
+       - previous transmit (to invalidate responses to the previous packet)
+       (the precision must be at least -30 to prevent an infinite loop!) */
+  } while (!UTI_IsZeroNtp64(&message.transmit_ts) &&
+           UTI_IsEqualAnyNtp64(&message.transmit_ts, &message.receive_ts,
+                               &message.originate_ts, local_ntp_tx));
+
   /* Generate the authentication data */
   if (auth) {
     if (!NAU_GenerateRequestAuth(auth, &message, &info)) {
@@ -1086,17 +1097,6 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
     }
   }
 
-    /* Do not send a packet with a non-zero transmit timestamp which is
-       equal to any of the following timestamps:
-       - receive (to allow reliable detection of the interleaved mode)
-       - originate (to prevent the packet from being its own valid response
-                    in the symmetric mode)
-       - previous transmit (to invalidate responses to the previous packet)
-       (the precision must be at least -30 to prevent an infinite loop!) */
-  } while (!UTI_IsZeroNtp64(&message.transmit_ts) &&
-           UTI_IsEqualAnyNtp64(&message.transmit_ts, &message.receive_ts,
-                               &message.originate_ts, local_ntp_tx));
-
   if (request_info && request_info->length < info.length) {
     DEBUG_LOG("Response longer than request req_len=%d res_len=%d",
               request_info->length, info.length);