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Date:      Tue, 5 Feb 2019 10:29:32 +0000 (UTC)
From:      Michael Tuexen <tuexen@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r343770 - head/sys/netinet
Message-ID:  <201902051029.x15ATWtt099892@repo.freebsd.org>
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Author: tuexen
Date: Tue Feb  5 10:29:31 2019
New Revision: 343770
URL: https://svnweb.freebsd.org/changeset/base/343770

Log:
  Only reduce the PMTU after the send call. The only way to increase it, is
  via PMTUD.
  
  This fixes an MTU issue reported by Timo Voelker.
  
  MFC after:		3 days

Modified:
  head/sys/netinet/sctp_output.c

Modified: head/sys/netinet/sctp_output.c
==============================================================================
--- head/sys/netinet/sctp_output.c	Tue Feb  5 10:13:51 2019	(r343769)
+++ head/sys/netinet/sctp_output.c	Tue Feb  5 10:29:31 2019	(r343770)
@@ -4289,10 +4289,12 @@ sctp_lowlevel_chunk_output(struct sctp_inpcb *inp,
 						if (net->port) {
 							mtu -= sizeof(struct udphdr);
 						}
-						if ((stcb != NULL) && (stcb->asoc.smallest_mtu > mtu)) {
-							sctp_mtu_size_reset(inp, &stcb->asoc, mtu);
+						if (mtu < net->mtu) {
+							if ((stcb != NULL) && (stcb->asoc.smallest_mtu > mtu)) {
+								sctp_mtu_size_reset(inp, &stcb->asoc, mtu);
+							}
+							net->mtu = mtu;
 						}
-						net->mtu = mtu;
 					}
 				} else if (ro->ro_rt == NULL) {
 					/* route was freed */
@@ -4647,10 +4649,12 @@ sctp_lowlevel_chunk_output(struct sctp_inpcb *inp,
 						if (net->port) {
 							mtu -= sizeof(struct udphdr);
 						}
-						if ((stcb != NULL) && (stcb->asoc.smallest_mtu > mtu)) {
-							sctp_mtu_size_reset(inp, &stcb->asoc, mtu);
+						if (mtu < net->mtu) {
+							if ((stcb != NULL) && (stcb->asoc.smallest_mtu > mtu)) {
+								sctp_mtu_size_reset(inp, &stcb->asoc, mtu);
+							}
+							net->mtu = mtu;
 						}
-						net->mtu = mtu;
 					}
 				} else if (ifp) {
 					if (ND_IFINFO(ifp)->linkmtu &&

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