rfc1323.patch by Ted - grendel@heorot.stanford.edu

Changes OpenBSD TCP/IP stack so that the RFC 1323 timestamp is set at
zero at the start of each connection.  Makes it impossible to
determine uptime, except as concerns that one connection.

cd /sys/netinet
patch < /.../rfc1323.patch
and rebuild kernel


--- tcp_var.h.orig  Thu Mar 15 18:26:39 2001
+++ tcp_var.h  Thu Mar 15 18:27:11 2001
@@ -161,6 +161,8 @@
   u_char  rcv_scale;    /* window scaling for recv window */
   u_char  request_r_scale;  /* pending window scaling */
   u_char  requested_s_scale;
+  u_int32_t mytcp_now;
+  u_int32_t oldtcp_now;
   u_int32_t ts_recent;    /* timestamp echo data */
   u_int32_t ts_recent_age;    /* when last updated */
   tcp_seq  last_ack_sent;
--- tcp_input.c.orig  Thu Mar 15 18:26:24 2001
+++ tcp_input.c  Thu Mar 15 18:26:55 2001
@@ -104,6 +104,7 @@
 int  tcprexmtthresh = 3;
 struct  tcpiphdr tcp_saveti;
 int  tcptv_keep_init = TCPTV_KEEP_INIT;
+u_int32_t ts_temp;
 
 extern u_long sb_max;
 
@@ -883,7 +884,10 @@
      * Fix from Braden, see Stevens p. 870
      */
     if (ts_present && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
-      tp->ts_recent_age = tcp_now;
+      ts_temp = tcp_now - tp->oldtcp_now;
+      tp->oldtcp_now = tcp_now;
+      tp->mytcp_now = ts_temp + tp->mytcp_now;
+      tp->ts_recent_age = tp->mytcp_now;
       tp->ts_recent = ts_val;
     }
 
@@ -897,7 +901,7 @@
          */
         ++tcpstat.tcps_predack;
         if (ts_present)
-          tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
+          tcp_xmit_timer(tp, tp->mytcp_now-ts_ecr+1);
         else if (tp->t_rtt &&
               SEQ_GT(th->th_ack, tp->t_rtseq))
           tcp_xmit_timer(tp, tp->t_rtt);
@@ -1015,7 +1019,6 @@
 #ifdef INET6
     register struct sockaddr_in6 *sin6;
 #endif /* INET6 */
-
     if (tiflags & TH_RST)
       goto drop;
     if (tiflags & TH_ACK)
@@ -1291,7 +1294,7 @@
       TSTMP_LT(ts_val, tp->ts_recent)) {
 
     /* Check to see if ts_recent is over 24 days old.  */
-    if ((int)(tcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
+    if ((int)(tp->mytcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
       /*
        * Invalidate ts_recent.  If this segment updates
        * ts_recent, the age will be reset later and ts_recent
@@ -1412,7 +1415,10 @@
    */
   if (ts_present && TSTMP_GEQ(ts_val, tp->ts_recent) &&
       SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
-    tp->ts_recent_age = tcp_now;
+    ts_temp = tcp_now - tp->oldtcp_now;
+    tp->oldtcp_now = tcp_now;
+    tp->mytcp_now = ts_temp + tp->mytcp_now;
+    tp->ts_recent_age = tp->mytcp_now;
     tp->ts_recent = ts_val;
   }
 
@@ -1733,7 +1739,7 @@
      * Recompute the initial retransmit timer.
      */
     if (ts_present)
-      tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
+      tcp_xmit_timer(tp, tp->mytcp_now-ts_ecr+1);
     else if (tp->t_rtt && SEQ_GT(th->th_ack, tp->t_rtseq))
       tcp_xmit_timer(tp,tp->t_rtt);
 
@@ -2214,7 +2220,9 @@
       if (th->th_flags & TH_SYN) {
         tp->t_flags |= TF_RCVD_TSTMP;
         tp->ts_recent = *ts_val;
-        tp->ts_recent_age = tcp_now;
+        tp->mytcp_now = 0;
+        tp->oldtcp_now = tcp_now;
+        tp->ts_recent_age = tp->mytcp_now;
       }
       break;
     
--- tcp_output.c.orig  Thu Mar 15 18:26:32 2001
+++ tcp_output.c  Thu Mar 15 18:27:03 2001
@@ -559,7 +559,7 @@
  
     /* Form timestamp option as shown in appendix A of RFC 1323. */
     *lp++ = htonl(TCPOPT_TSTAMP_HDR);
-    *lp++ = htonl(tcp_now);
+    *lp++ = htonl(tp->mytcp_now);
     *lp   = htonl(tp->ts_recent);
     optlen += TCPOLEN_TSTAMP_APPA;
   }