The branch stable/13 has been updated by rscheff:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=703419774f86525a2441d615733993a6fddcd047

commit 703419774f86525a2441d615733993a6fddcd047
Author:     Richard Scheffenegger <[email protected]>
AuthorDate: 2021-03-17 15:44:29 +0000
Commit:     Richard Scheffenegger <[email protected]>
CommitDate: 2021-03-17 19:05:33 +0000

    fix panic when rescue retransmission and FIN overlap
    
    PR:           254244
    PR:           254309
    Reviewed By:  #transport, hselasky, tuexen
    Approved by:  re (cperciva)
    MFC after:    immediately
    Sponsored By: NetApp, Inc.
    Differential Revision: https://reviews.freebsd.org/D29315
    
    (cherry picked from commit e9f029831fa5747ae1b405f5716c52cb4ebf1e04)
---
 sys/netinet/tcp_sack.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
index 37db30007580..f8d983da723b 100644
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -831,8 +831,18 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
            (tp->snd_recover == tp->snd_max) &&
            TAILQ_EMPTY(&tp->snd_holes) &&
            (tp->sackhint.delivered_data > 0)) {
-               struct sackhole *hole;
-               hole = tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack, tp->snd_max 
- maxseg), tp->snd_max, NULL);
+               /*
+                * Exclude FIN sequence space in
+                * the hole for the rescue retransmission,
+                * and also don't create a hole, if only
+                * the ACK for a FIN is outstanding.
+                */
+               tcp_seq highdata = tp->snd_max;
+               if (tp->t_flags & TF_SENTFIN)
+                       highdata--;
+               if (th->th_ack != highdata)
+                       (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
+                           highdata - maxseg), highdata, NULL);
        }
        (void) tp->t_fb->tfb_tcp_output(tp);
 }
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