git: b9dc12859790 - stable/12 - tcp: tolerate missing timestamps

[Michael Tuexen]

The branch stable/12 has been updated by tuexen:

URL: https://cgit.FreeBSD.org/src/commit/?id=b9dc1285979058cb2751675d926a773513e83fc8

commit b9dc1285979058cb2751675d926a773513e83fc8
Author:     Michael Tuexen <tuexen at FreeBSD.org>
AuthorDate: 2021-06-11 18:14:34 +0000
Commit:     Michael Tuexen <tuexen at FreeBSD.org>
CommitDate: 2021-07-14 07:43:16 +0000

    tcp: tolerate missing timestamps
    
    Some TCP stacks negotiate TS support, but do not send TS at all
    or not for keep-alive segments. Since this includes modern widely
    deployed stacks, tolerate the violation of RFC 7323 per default.
    
    Reviewed by:            rgrimes, rrs, rscheff
    Differential Revision:  https://reviews.freebsd.org/D30740
    Sponsored by:           Netflix, Inc.
    
    (cherry picked from commit 870af3f4dc57a6bbfc03f6a49ca0d5b7ff1b975a)
---
 share/man/man4/tcp.4   | 6 ++++--
 sys/netinet/tcp_subr.c | 9 ++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index e1e87afd7fd6..ad7e3f117d68 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd January 14, 2021
+.Dd June 27, 2021
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -343,7 +343,9 @@ segments belonging to
 connections for which support of
 .Tn TCP
 timestamps has been negotiated.
-(default is 0, i.e., the missing of timestamps is not tolerated).
+As of June 2021, several TCP stacks are known to violate RFC 7323, including
+modern widely deployed ones.
+Therefore the default is 1, i.e., the missing of timestamps is tolerated.
 .It Dv TCPCTL_MSSDFLT
 .Pq Va mssdflt
 The default value used for the maximum segment size
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 5394a63c1a12..c82a5bf21a15 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -195,7 +195,14 @@ SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1323, rfc1323, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_rfc1323), 0,
     "Enable rfc1323 (high performance TCP) extensions");
 
-VNET_DEFINE(int, tcp_tolerate_missing_ts) = 0;
+/*
+ * As of June 2021, several TCP stacks violate RFC 7323 from September 2014.
+ * Some stacks negotiate TS, but never send them after connection setup. Some
+ * stacks negotiate TS, but don't send them when sending keep-alive segments.
+ * These include modern widely deployed TCP stacks.
+ * Therefore tolerating violations for now...
+ */
+VNET_DEFINE(int, tcp_tolerate_missing_ts) = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tolerate_missing_ts, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_tolerate_missing_ts), 0,
     "Tolerate missing TCP timestamps");