A patch against FreeBSD-SA-05:15.tcp

[Noritoshi Demizu <demizu@xxxxxxxxxxxxxx>]

Below is a patch to fix the problem described in FreeBSD-SA-05:15.tcp,
which refers CAN-2005-0356 (or CERT VU#637934) and CAN-2005-2068.
( ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:15.tcp.asc )

It is imported from FreeBSD (tcp_input.c 1.270, 1.278 & tcp_seq.h 1.25).

- The changes of tcp_input.c 1.270 and tcp_seq.h 1.25 were originally
  submitted by Raja Mukerji and reviewed by Mohan Srinivasan and me.
  These changes fixed CAN-2005-0356 (or CERT VU#637934).

- The change of tcp_input.c 1.278 was originally submitted by me
  and reviewed by Andre Oppermann and Mohan Srinivasan.
  This change fixed CAN-2005-2068.

The patch below includes all changes above.  I'd like to commit this
patch if no objection is raised until August 28, 2005.

Regards,
Noritoshi Demizu


Index: tcp_input.c
===================================================================
RCS file: /home/cvsup/DragonFlyBSD/dcvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.60
diff -u -r1.60 tcp_input.c
--- tcp_input.c	10 May 2005 15:48:10 -0000	1.60
+++ tcp_input.c	24 Aug 2005 09:31:58 -0000
@@ -1078,7 +1078,7 @@
 	 * XXX this is tradtitional behavior, may need to be cleaned up.
 	 */
 	tcp_dooptions(&to, optp, optlen, (thflags & TH_SYN) != 0);
-	if (thflags & TH_SYN) {
+	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
 		if (to.to_flags & TOF_SCALE) {
 			tp->t_flags |= TF_RCVD_SCALE;
 			tp->requested_s_scale = to.to_requested_s_scale;
@@ -1795,10 +1795,25 @@
 	/*
 	 * If last ACK falls within this segment's sequence numbers,
 	 * record its timestamp.
-	 * NOTE that the test is modified according to the latest
-	 * proposal of the tcplw@xxxxxxxx list (Braden 1993/04/26).
-	 */
-	if ((to.to_flags & TOF_TS) && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
+	 * NOTE:
+	 * 1) That the test incorporates suggestions from the latest
+	 *    proposal of the tcplw@xxxxxxxx list (Braden 1993/04/26).
+	 * 2) That updating only on newer timestamps interferes with
+	 *    our earlier PAWS tests, so this check should be solely
+	 *    predicated on the sequence space of this segment.
+	 * 3) That we modify the segment boundary check to be
+	 *        Last.ACK.Sent <= SEG.SEQ + SEG.LEN
+	 *    instead of RFC1323's
+	 *        Last.ACK.Sent < SEG.SEQ + SEG.LEN,
+	 *    This modified check allows us to overcome RFC1323's
+	 *    limitations as described in Stevens TCP/IP Illustrated
+	 *    Vol. 2 p.869. In such cases, we can still calculate the
+	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
+	 */
+	if ((to.to_flags & TOF_TS) && SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
+	    SEQ_LEQ(tp->last_ack_sent, (th->th_seq + tlen
+					+ ((thflags & TH_SYN) != 0)
+					+ ((thflags & TH_FIN) != 0)))) {
 		tp->ts_recent_age = ticks;
 		tp->ts_recent = to.to_tsval;
 	}
@@ -2678,6 +2693,12 @@
 			to->to_tsval = ntohl(to->to_tsval);
 			bcopy(cp + 6, &to->to_tsecr, sizeof to->to_tsecr);
 			to->to_tsecr = ntohl(to->to_tsecr);
+			/*
+			 * If echoed timestamp is later than the current time,
+			 * fall back to non RFC1323 RTT calculation.
+			 */
+			if (to->to_tsecr != 0 && TSTMP_GT(to->to_tsecr, ticks))
+				to->to_tsecr = 0;
 			break;
 		case TCPOPT_CC:
 			if (optlen != TCPOLEN_CC)
Index: tcp_seq.h
===================================================================
RCS file: /home/cvsup/DragonFlyBSD/dcvs/src/sys/netinet/tcp_seq.h,v
retrieving revision 1.7
diff -u -r1.7 tcp_seq.h
--- tcp_seq.h	21 Dec 2004 02:54:15 -0000	1.7
+++ tcp_seq.h	24 Aug 2005 09:31:58 -0000
@@ -111,6 +111,7 @@
 
 /* for modulo comparisons of timestamps */
 #define TSTMP_LT(a,b)	((int)((a)-(b)) < 0)
+#define TSTMP_GT(a,b)	((int)((a)-(b)) > 0)
 #define TSTMP_GEQ(a,b)	((int)((a)-(b)) >= 0)
 
 /*