git: e754d89bba8c - stable/14 - tcp: fix detection of bad RTOs

The branch stable/14 has been updated by tuexen:

URL: https://cgit.FreeBSD.org/src/commit/?id=e754d89bba8c526fd1ff792616ff4cbf9c6e093e

commit e754d89bba8c526fd1ff792616ff4cbf9c6e093e
Author:     Michael Tuexen <tuexen@FreeBSD.org>
AuthorDate: 2025-03-20 15:17:40 +0000
Commit:     Michael Tuexen <tuexen@FreeBSD.org>
CommitDate: 2025-04-04 09:05:10 +0000

    tcp: fix detection of bad RTOs
    
    If timestamps are enabled, the actions performed by a retransmission
    timeout were rolled back, when they should not.
    It is needed to make sure the incoming segment advances SND.UNA.
    To do this, remove the incorrect upfront check and extend the check in
    the fast path to handle also the case of timestamps.
    
    PR:                     282605
    Reviewed by:            cc, rscheff, Peter Lei
    Sponsored by:           Netflix, Inc.
    Differential Revision:  https://reviews.freebsd.org/D49414
    
    (cherry picked from commit fbcf3b74e8f2c0c5ba37f1839bfe9395eb2fd0b1)
---
 sys/netinet/tcp_input.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index c868ba648bd7..104e98436f0c 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1637,11 +1637,6 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 		to.to_tsecr -= tp->ts_offset;
 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
 			to.to_tsecr = 0;
-		else if (tp->t_rxtshift == 1 &&
-			 tp->t_flags & TF_PREVVALID &&
-			 tp->t_badrxtwin != 0 &&
-			 TSTMP_LT(to.to_tsecr, tp->t_badrxtwin))
-			cc_cong_signal(tp, th, CC_RTO_ERR);
 	}
 	/*
 	 * Process options only when we get SYN/ACK back. The SYN case
@@ -1786,15 +1781,17 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 				TCPSTAT_INC(tcps_predack);
 
 				/*
-				 * "bad retransmit" recovery without timestamps.
+				 * "bad retransmit" recovery.
 				 */
-				if ((to.to_flags & TOF_TS) == 0 &&
-				    tp->t_rxtshift == 1 &&
+				if (tp->t_rxtshift == 1 &&
 				    tp->t_flags & TF_PREVVALID &&
 				    tp->t_badrxtwin != 0 &&
-				    TSTMP_LT(ticks, tp->t_badrxtwin)) {
+				    (((to.to_flags & TOF_TS) != 0 &&
+				      to.to_tsecr != 0 &&
+				      TSTMP_LT(to.to_tsecr, tp->t_badrxtwin)) ||
+				     ((to.to_flags & TOF_TS) == 0 &&
+				      TSTMP_LT(ticks, tp->t_badrxtwin))))
 					cc_cong_signal(tp, th, CC_RTO_ERR);
-				}
 
 				/*
 				 * Recalculate the transmit timer / rtt.