sctp: only update outstanding_bytes for transmitted queue when doing prsctp_prune

Now outstanding_bytes is only increased when appending chunks into one
packet and sending it at 1st time, while decreased when it is about to
move into retransmit queue. It means outstanding_bytes value is already
decreased for all chunks in retransmit queue.

However sctp_prsctp_prune_sent is a common function to check the chunks
in both transmitted and retransmit queue, it decrease outstanding_bytes
when moving a chunk into abandoned queue from either of them.

It could cause outstanding_bytes underflow, as it also decreases it's
value for the chunks in retransmit queue.

This patch fixes it by only updating outstanding_bytes for transmitted
queue when pruning queues for prsctp prio policy, the same fix is also
needed in sctp_check_transmitted.

Fixes: 8dbdf1f5b09c ("sctp: implement prsctp PRIO policy")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/outqueue.c

@@ -377,7 +377,8 @@ static int sctp_prsctp_prune_sent(struct sctp_association *asoc,
 		asoc->abandoned_sent[SCTP_PR_INDEX(PRIO)]++;
 		streamout->ext->abandoned_sent[SCTP_PR_INDEX(PRIO)]++;
 
-		if (!chk->tsn_gap_acked) {
+		if (queue != &asoc->outqueue.retransmit &&
+		    !chk->tsn_gap_acked) {
 			if (chk->transport)
 				chk->transport->flight_size -=
 						sctp_data_size(chk);
@@ -1434,7 +1435,8 @@ static void sctp_check_transmitted(struct sctp_outq *q,
 			/* If this chunk has not been acked, stop
 			 * considering it as 'outstanding'.
 			 */
-			if (!tchunk->tsn_gap_acked) {
+			if (transmitted_queue != &q->retransmit &&
+			    !tchunk->tsn_gap_acked) {
 				if (tchunk->transport)
 					tchunk->transport->flight_size -=
 							sctp_data_size(tchunk);