From d59909c3e2f4fbe0fcdbc1de1f205f568409c527 Mon Sep 17 00:00:00 2001
From: Michael Tuexen <tuexen@FreeBSD.org>
Date: Thu, 26 Mar 2015 22:05:31 +0000
Subject: [PATCH] Improve the selection of the destination address of SACK
 chunks. This fixes https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=196755
 and is joint work with rrs@.

MFC after: 1 week
---
 sys/netinet/sctp_output.c  | 23 ++++-------------------
 sys/netinet/sctp_structs.h |  1 -
 2 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/sys/netinet/sctp_output.c b/sys/netinet/sctp_output.c
index c16e75f7f15d..cb59dab5359d 100644
--- a/sys/netinet/sctp_output.c
+++ b/sys/netinet/sctp_output.c
@@ -10409,32 +10409,17 @@ sctp_send_sack(struct sctp_tcb *stcb, int so_locked
 	a_chk->sent = SCTP_DATAGRAM_UNSENT;
 	a_chk->whoTo = NULL;
 
-	if ((asoc->numduptsns) ||
-	    (!(asoc->last_data_chunk_from->dest_state & SCTP_ADDR_REACHABLE))) {
+	if (!(asoc->last_data_chunk_from->dest_state & SCTP_ADDR_REACHABLE)) {
 		/*-
-		 * Ok, we have some duplicates or the destination for the
-		 * sack is unreachable, lets see if we can select an
-		 * alternate than asoc->last_data_chunk_from
+		 * Ok, the destination for the SACK is unreachable, lets see if
+		 * we can select an alternate to asoc->last_data_chunk_from
 		 */
-		if ((asoc->last_data_chunk_from->dest_state & SCTP_ADDR_REACHABLE) &&
-		    (asoc->used_alt_onsack > asoc->numnets)) {
-			/* We used an alt last time, don't this time */
-			a_chk->whoTo = NULL;
-		} else {
-			asoc->used_alt_onsack++;
-			a_chk->whoTo = sctp_find_alternate_net(stcb, asoc->last_data_chunk_from, 0);
-		}
+		a_chk->whoTo = sctp_find_alternate_net(stcb, asoc->last_data_chunk_from, 0);
 		if (a_chk->whoTo == NULL) {
 			/* Nope, no alternate */
 			a_chk->whoTo = asoc->last_data_chunk_from;
-			asoc->used_alt_onsack = 0;
 		}
 	} else {
-		/*
-		 * No duplicates so we use the last place we received data
-		 * from.
-		 */
-		asoc->used_alt_onsack = 0;
 		a_chk->whoTo = asoc->last_data_chunk_from;
 	}
 	if (a_chk->whoTo) {
diff --git a/sys/netinet/sctp_structs.h b/sys/netinet/sctp_structs.h
index b1df17dbf3bf..8f61cd7b19db 100644
--- a/sys/netinet/sctp_structs.h
+++ b/sys/netinet/sctp_structs.h
@@ -1174,7 +1174,6 @@ struct sctp_association {
 
 	struct sctp_scoping scope;
 	/* flags to handle send alternate net tracking */
-	uint8_t used_alt_onsack;
 	uint8_t used_alt_asconfack;
 	uint8_t fast_retran_loss_recovery;
 	uint8_t sat_t3_loss_recovery;