git: 724ad12c947d - stable/15 - tcp: use RFC 6191 for connection recycling in TIME-WAIT

The branch stable/15 has been updated by tuexen:

URL: https://cgit.FreeBSD.org/src/commit/?id=724ad12c947dabaa9f62f81f4342a738e0f42971

commit 724ad12c947dabaa9f62f81f4342a738e0f42971
Author:     Michael Tuexen <tuexen@FreeBSD.org>
AuthorDate: 2026-04-17 07:11:41 +0000
Commit:     Michael Tuexen <tuexen@FreeBSD.org>
CommitDate: 2026-04-26 08:09:03 +0000

    tcp: use RFC 6191 for connection recycling in TIME-WAIT
    
    Implement the criteria specified in RFC 6191 for recycling TCP
    connections in TIME-WAIT.
    
    Reviewed by:            rscheff, Marius Halden
    Sponsored by:           Netflix, Inc.
    Differential Revision:  https://reviews.freebsd.org/D56321
    Event:                  Wiesbaden Hackathon 2026
    
    (cherry picked from commit 3a54aa3b0911bef15e014b8a8185e116efb0a918)
---
 sys/netinet/tcp_timewait.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 66103f8d0b11..d90178ee03ec 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -261,12 +261,17 @@ tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
 	/*
 	 * If a new connection request is received
 	 * while in TIME_WAIT, drop the old connection
-	 * and start over if the sequence numbers
-	 * are above the previous ones.
+	 * and start over if allowed by RFC 6191.
 	 * Allow UDP port number changes in this case.
 	 */
 	if (((thflags & (TH_SYN | TH_ACK)) == TH_SYN) &&
-	    SEQ_GT(th->th_seq, tp->rcv_nxt)) {
+	    ((((tp->t_flags & TF_RCVD_TSTMP) != 0) &&
+	      ((to->to_flags & TOF_TS) != 0) &&
+	      TSTMP_LT(tp->ts_recent, to->to_tsval)) ||
+	     (((tp->t_flags & TF_RCVD_TSTMP) == 0) &&
+	      ((to->to_flags & TOF_TS) != 0) &&
+	      (V_tcp_tolerate_missing_ts == 0)) ||
+	     SEQ_GT(th->th_seq, tp->rcv_nxt))) {
 		/*
 		 * In case we can't upgrade our lock just pretend we have
 		 * lost this packet.