tcp: drop data received after a FIN has been processed

RFC 9293 describes the handling of data in the CLOSE-WAIT, CLOSING,
LAST-ACK, and TIME-WAIT states:
This should not occur since a FIN has been received from the remote
side. Ignore the segment text.
Therefore, implement this handling.

Reviewed by:		rrs, rscheff
MFC after:		3 days
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D44746

sys/netinet/tcp_input.c

@@ -2337,9 +2337,11 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 
 	/*
 	 * If new data are received on a connection after the
-	 * user processes are gone, then RST the other end.
+	 * user processes are gone, then RST the other end if
+	 * no FIN has been processed.
 	 */
-	if ((tp->t_flags & TF_CLOSED) && tlen) {
+	if ((tp->t_flags & TF_CLOSED) && tlen > 0 &&
+	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
 			    "after socket was closed, "

sys/netinet/tcp_stacks/bbr.c

@@ -9555,15 +9555,6 @@ bbr_do_closing(struct mbuf *m, struct tcphdr *th, struct socket *so,
 	if (ctf_drop_checks(to, m, th, tp, &tlen, &thflags, &drop_hdrlen, &ret_val)) {
 		return (ret_val);
 	}
-	/*
-	 * If new data are received on a connection after the user processes
-	 * are gone, then RST the other end.
-	 * We call a new function now so we might continue and setup
-	 * to reset at all data being ack'd.
-	 */
-	if ((tp->t_flags & TF_CLOSED) && tlen &&
-	    bbr_check_data_after_close(m, bbr, tp, &tlen, th, so))
-		return (1);
 	/*
 	 * If last ACK falls within this segment's sequence numbers, record
 	 * its timestamp. NOTE: 1) That the test incorporates suggestions
@@ -9666,15 +9657,6 @@ bbr_do_lastack(struct mbuf *m, struct tcphdr *th, struct socket *so,
 	if (ctf_drop_checks(to, m, th, tp, &tlen, &thflags, &drop_hdrlen, &ret_val)) {
 		return (ret_val);
 	}
-	/*
-	 * If new data are received on a connection after the user processes
-	 * are gone, then RST the other end.
-	 * We call a new function now so we might continue and setup
-	 * to reset at all data being ack'd.
-	 */
-	if ((tp->t_flags & TF_CLOSED) && tlen &&
-	    bbr_check_data_after_close(m, bbr, tp, &tlen, th, so))
-		return (1);
 	/*
 	 * If last ACK falls within this segment's sequence numbers, record
 	 * its timestamp. NOTE: 1) That the test incorporates suggestions

sys/netinet/tcp_stacks/rack.c

@@ -14997,13 +14997,6 @@ rack_do_closing(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			      &rack->r_ctl.challenge_ack_cnt)) {
 		return (ret_val);
 	}
-	/*
-	 * If new data are received on a connection after the user processes
-	 * are gone, then RST the other end.
-	 */
-	if ((tp->t_flags & TF_CLOSED) && tlen &&
-	    rack_check_data_after_close(m, tp, &tlen, th, so))
-		return (1);
 	/*
 	 * If last ACK falls within this segment's sequence numbers, record
 	 * its timestamp. NOTE: 1) That the test incorporates suggestions
@@ -15112,13 +15105,6 @@ rack_do_lastack(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			      &rack->r_ctl.challenge_ack_cnt)) {
 		return (ret_val);
 	}
-	/*
-	 * If new data are received on a connection after the user processes
-	 * are gone, then RST the other end.
-	 */
-	if ((tp->t_flags & TF_CLOSED) && tlen &&
-	    rack_check_data_after_close(m, tp, &tlen, th, so))
-		return (1);
 	/*
 	 * If last ACK falls within this segment's sequence numbers, record
 	 * its timestamp. NOTE: 1) That the test incorporates suggestions