[PATCH 3.16.y-ckt 022/180] sctp: start t5 timer only when peer rwnd is 0 and local state is SHUTDOWN_PENDING

[Luis Henriques]

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: lucien <lucien.xin at gmail.com>

commit 8a0d19c5ed417c78d03f4e0fa7215e58c40896d8 upstream.

when A sends a data to B, then A close() and enter into SHUTDOWN_PENDING
state, if B neither claim his rwnd is 0 nor send SACK for this data, A
will keep retransmitting this data until t5 timeout, Max.Retrans times
can't work anymore, which is bad.

if B's rwnd is not 0, it should send abort after Max.Retrans times, only
when B's rwnd == 0 and A's retransmitting beyonds Max.Retrans times, A
will start t5 timer, which is also commit f8d960524328 ("sctp: Enforce
retransmission limit during shutdown") means, but it lacks the condition
peer rwnd == 0.

so fix it by adding a bit (zero_window_announced) in peer to record if
the last rwnd is 0. If it was, zero_window_announced will be set. and use
this bit to decide if start t5 timer when local.state is SHUTDOWN_PENDING.

Fixes: commit f8d960524328 ("sctp: Enforce retransmission limit during shutdown")
Signed-off-by: Xin Long <lucien.xin at gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 include/net/sctp/structs.h | 3 ++-
 net/sctp/outqueue.c        | 1 +
 net/sctp/sm_statefuns.c    | 3 ++-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index ec526e69daeb..2f256a202e97 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1492,7 +1492,8 @@ struct sctp_association {
 		 *             : SACK's are not delayed (see Section 6).
 		 */
 		__u8    sack_needed:1,     /* Do we need to sack the peer? */
-			sack_generation:1;
+			sack_generation:1,
+			zero_window_announced:1;
 		__u32	sack_cnt;
 
 		__u32   adaptation_ind;	 /* Adaptation Code point. */
diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
index 9c77947c0597..53e5962f3a05 100644
--- a/net/sctp/outqueue.c
+++ b/net/sctp/outqueue.c
@@ -1252,6 +1252,7 @@ int sctp_outq_sack(struct sctp_outq *q, struct sctp_chunk *chunk)
 	 */
 
 	sack_a_rwnd = ntohl(sack->a_rwnd);
+	asoc->peer.zero_window_announced = !sack_a_rwnd;
 	outstanding = q->outstanding_bytes;
 
 	if (outstanding < sack_a_rwnd)
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index af1da3188865..4f03bd0cb44d 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -5418,7 +5418,8 @@ sctp_disposition_t sctp_sf_do_6_3_3_rtx(struct net *net,
 	SCTP_INC_STATS(net, SCTP_MIB_T3_RTX_EXPIREDS);
 
 	if (asoc->overall_error_count >= asoc->max_retrans) {
-		if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING) {
+		if (asoc->peer.zero_window_announced &&
+		    asoc->state == SCTP_STATE_SHUTDOWN_PENDING) {
 			/*
 			 * We are here likely because the receiver had its rwnd
 			 * closed for a while and we have not been able to