sctp: set sender next_tsn for the old result with ctsn_ack_point plus 1

When doing asoc reset, if the sender of the response has already sent some
chunk and increased asoc->next_tsn before the duplicate request comes, the
response will use the old result with an incorrect sender next_tsn.

Better than asoc->next_tsn, asoc->ctsn_ack_point can't be changed after
the sender of the response has performed the asoc reset and before the
peer has confirmed it, and it's value is still asoc->next_tsn original
value minus 1.

This patch sets sender next_tsn for the old result with ctsn_ack_point
plus 1 when processing the duplicate request, to make sure the sender
next_tsn value peer gets will be always right.

Fixes: 692787ce ("sctp: implement receiver-side procedures for the SSN/TSN Reset Request Parameter")
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/stream.c

@@ -725,7 +725,7 @@ struct sctp_chunk *sctp_process_strreset_tsnreq(
 		i = asoc->strreset_inseq - request_seq - 1;
 		result = asoc->strreset_result[i];
 		if (result == SCTP_STRRESET_PERFORMED) {
-			next_tsn = asoc->next_tsn;
+			next_tsn = asoc->ctsn_ack_point + 1;
 			init_tsn =
 				sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map) + 1;
 		}