Update tcp_lro with tested bugfixes from Netflix and LLNW:

    rrs - Lets make the LRO code look for true dup-acks and window update acks
          fly on through and combine.
    rrs - Make the LRO engine a bit more aware of ack-only seq space. Lets not
          have it incorrectly wipe out newer acks for older acks when we have
          out-of-order acks (common in wifi environments).
    jeggleston - LRO eating window updates

Based on all of the above I think we are RFC compliant doing it this way:

https://tools.ietf.org/html/rfc1122

section 4.2.2.16

"Note that TCP has a heuristic to select the latest window update despite
possible datagram reordering; as a result, it may ignore a window update with
a smaller window than previously offered if neither the sequence number nor the
acknowledgment number is increased."

Submitted by:	Kevin Bowling <kevin.bowling@kev009.com>
Reviewed by:	rstone gallatin
Sponsored by:	NetFlix and Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D14540

1 files changed, 18 insertions, 7 deletions

diff --git a/sys/netinet/tcp_lro.c b/sys/netinet/tcp_lro.c
index c859344135f0..0061df3ecaa8 100644
--- a/sys/netinet/tcp_lro.c
+++ b/sys/netinet/tcp_lro.c
@@ -57,6 +57,7 @@ __FBSDID("$FreeBSD$");
 #include <netinet/ip.h>
 #include <netinet/ip_var.h>
 #include <netinet/tcp.h>
+#include <netinet/tcp_seq.h>
 #include <netinet/tcp_lro.h>
 #include <netinet/tcp_var.h>
 
@@ -794,7 +795,9 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
 
 		/* Try to append the new segment. */
 		if (__predict_false(seq != le->next_seq ||
-		    (tcp_data_len == 0 && le->ack_seq == th->th_ack))) {
+		    (tcp_data_len == 0 &&
+		    le->ack_seq == th->th_ack &&
+		    le->window == th->th_win))) {
 			/* Out of order packet or duplicate ACK. */
 			tcp_lro_active_remove(le);
 			tcp_lro_flush(lc, le);
@@ -811,12 +814,20 @@ tcp_lro_rx2(struct lro_ctrl *lc, struct mbuf *m, uint32_t csum, int use_hash)
 			le->tsval = tsval;
 			le->tsecr = *(ts_ptr + 2);
 		}
-
-		le->next_seq += tcp_data_len;
-		le->ack_seq = th->th_ack;
-		le->window = th->th_win;
-		le->append_cnt++;
-
+		if (tcp_data_len || SEQ_GT(ntohl(th->th_ack), ntohl(le->ack_seq))) {
+			le->next_seq += tcp_data_len;
+			le->ack_seq = th->th_ack;
+			le->window = th->th_win;
+			le->append_cnt++;
+		} else if (th->th_ack == le->ack_seq) {
+			le->window = WIN_MAX(le->window, th->th_win);
+			le->append_cnt++;
+		} else {
+			/* no data and old ack */
+			le->append_cnt++;
+			m_freem(m);
+			return (0);
+		}
 #ifdef TCP_LRO_UPDATE_CSUM
 		le->ulp_csum += tcp_lro_rx_csum_fixup(le, l3hdr, th,
 		    tcp_data_len, ~csum);