From 331721f5c85bb66dbd6e3f67c09e6442584e07d5 Mon Sep 17 00:00:00 2001
From: Sepherosa Ziehau <sephe@dragonflybsd.org>
Date: Tue, 8 May 2012 13:56:07 +0800
Subject: [PATCH] tcp/sack: Guard against ACK reordering when adding SACK
 blocks

The reordered ACK could carry SACK blocks which are all covered by
tcpcb.snd_una
---
 sys/netinet/tcp_sack.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
index 403185e606..ea29afb565 100644
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -311,7 +311,11 @@ tcp_sack_add_blocks(struct tcpcb *tp, struct tcpopt *to)
 		boolean_t update;
 		int error;
 
-		/* don't accept bad SACK blocks */
+		/* Guard against ACK reordering */
+		if (SEQ_LT(newsackblock->rblk_start, tp->snd_una))
+			continue;
+
+		/* Don't accept bad SACK blocks */
 		if (SEQ_GT(newsackblock->rblk_end, tp->snd_max)) {
 			tcpstat.tcps_rcvbadsackopt++;
 			break;		/* skip all other blocks */
-- 
2.41.0