svn commit: r364054 - head/sys/netinet

[Michael Tuexen]

Author: tuexen
Date: Sat Aug  8 19:39:38 2020
New Revision: 364054
URL: https://svnweb.freebsd.org/changeset/base/364054

Log:
  Improve the ECN negotiation when the TCP SYN-cache is used by making
  sure that
  * ECN is disabled if the client sends an non-ECN-setup SYN segment.
  * ECN is disabled is the ECN-setup SYN-ACK segment is retransmitted more
    than net.inet.tcp.ecn.maxretries times.
  
  Reviewed by:		rscheff
  MFC after:		1 week
  Sponsored by:		Netflix, Inc.
  Differential Revision:	https://reviews.freebsd.org/D26008

Modified:
  head/sys/netinet/tcp_syncache.c

Modified: head/sys/netinet/tcp_syncache.c
==============================================================================
--- head/sys/netinet/tcp_syncache.c	Sat Aug  8 16:56:20 2020	(r364053)
+++ head/sys/netinet/tcp_syncache.c	Sat Aug  8 19:39:38 2020	(r364054)
@@ -510,6 +510,9 @@ syncache_timer(void *xsch)
 				sch->sch_nextc = sc->sc_rxttime;
 			continue;
 		}
+		if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
+			sc->sc_flags &= ~SCF_ECN;
+		}
 		if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
 			if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
 				log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
@@ -1505,6 +1508,13 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *t
 			sc->sc_tsreflect = to->to_tsval;
 		else
 			sc->sc_flags &= ~SCF_TIMESTAMP;
+		/*
+		 * Disable ECN if needed.
+		 */
+		if ((sc->sc_flags & SCF_ECN) &&
+		    ((th->th_flags & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) {
+			sc->sc_flags &= ~SCF_ECN;
+		}
 #ifdef MAC
 		/*
 		 * Since we have already unconditionally allocated label