git: 8c69d988a8d3 - main - tcp: When we have an out-of-order FIN we do want to strip off the FIN bit.

[Randall Stewart]

The branch main has been updated by rrs:

URL: https://cgit.FreeBSD.org/src/commit/?id=8c69d988a8d32e53310c7b73ec8721b04b7249e6

commit 8c69d988a8d32e53310c7b73ec8721b04b7249e6
Author:     Randall Stewart <rrs at FreeBSD.org>
AuthorDate: 2021-05-27 14:50:32 +0000
Commit:     Randall Stewart <rrs at FreeBSD.org>
CommitDate: 2021-05-27 14:50:32 +0000

    tcp: When we have an out-of-order FIN we do want to strip off the FIN bit.
    
    The last set of commits fixed both a panic (in rack) and an ACK-war (in freebsd and bbr).
    However there was a missing case, i.e. where we get an out-of-order FIN by itself.
    In such a case we don't want to leave the FIN bit set, otherwise we will do the
    wrong thing and ack the FIN incorrectly. Instead we need to go through the
    tcp_reasm() code and that way the FIN will be stripped and all will be well.
    
    Reviewed by: mtuexen,rscheff
    Sponsored by: Netflix Inc
    Differential Revision:  https://reviews.freebsd.org/D30497
---
 sys/netinet/tcp_input.c       | 7 ++++++-
 sys/netinet/tcp_stacks/bbr.c  | 7 ++++++-
 sys/netinet/tcp_stacks/rack.c | 7 ++++++-
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index b9836a137608..1dab2e511d95 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -3191,7 +3191,12 @@ dodata:							/* XXX */
 			 * when trimming from the head.
 			 */
 			tcp_seq temp = save_start;
-			if (tlen) {
+			if (tlen || (th->th_seq != tp->rcv_nxt)) {
+				/*
+				 * We add the th_seq != rcv_nxt to
+				 * catch the case of a stand alone out
+				 * of order FIN.
+				 */
 				thflags = tcp_reass(tp, th, &temp, &tlen, m);
 				tp->t_flags |= TF_ACKNOW;
 			}
diff --git a/sys/netinet/tcp_stacks/bbr.c b/sys/netinet/tcp_stacks/bbr.c
index b2fc5c1f928e..5b97c3d7800f 100644
--- a/sys/netinet/tcp_stacks/bbr.c
+++ b/sys/netinet/tcp_stacks/bbr.c
@@ -8320,7 +8320,12 @@ bbr_process_data(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			 * trimming from the head.
 			 */
 			tcp_seq temp = save_start;
-			if (tlen) {
+			if (tlen || (th->th_seq != tp->rcv_nxt)) {
+				/*
+				 * We add the th_seq != rcv_nxt to
+				 * catch the case of a stand alone out
+				 * of order FIN.
+				 */
 				thflags = tcp_reass(tp, th, &temp, &tlen, m);
 				tp->t_flags |= TF_ACKNOW;
 			}
diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
index b7e8c1578f2b..1db09e30d968 100644
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -10235,7 +10235,12 @@ rack_process_data(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			 * trimming from the head.
 			 */
 			tcp_seq temp = save_start;
-			if (tlen) {
+			if (tlen || (th->th_seq != tp->rcv_nxt)) {
+				/*
+				 * We add the th_seq != rcv_nxt to
+				 * catch the case of a stand alone out
+				 * of order FIN.
+				 */
 				thflags = tcp_reass(tp, th, &temp, &tlen, m);
 				tp->t_flags |= TF_ACKNOW;
 			}