: Sequence number wraparound issues

[CCID2]: Sequence number wraparound issues

This replaces several uses of standard arithmetic with the DCCP sequence number arithmetic functions. The problem here is that the sequence number wrap-around was not taken into consideration.

* Condition "seqp->ccid2s_seq <= prev->ccid2s_seq" has been replaced by dccp_delta_seqno(seqp->ccid2s_seq, prev->ccid2s_seq) >= 0 since if seqp is `before' prev, then the delta_seqno() is positive.

* The test whether sequence numbers a' and b' are consecutive has the form dccp_delta_seqno(a, b) = 1

* Increment of ccid2hctx_rpseq could be done using dccp_inc_seqno(), but since here the incremented ccid2hctx_rpseq = seqno, used assignment instead.

---
 net/dccp/ccids/ccid2.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

@@ -59,7 +59,8 @@ static void ccid2_hc_tx_check_sanity(con
 				pipe++;
 
 			/* packets are sent sequentially */
-			BUG_ON(seqp->ccid2s_seq <= prev->ccid2s_seq);
+			BUG_ON(dccp_delta_seqno(seqp->ccid2s_seq,
+						prev->ccid2s_seq ) >= 0);
 			BUG_ON(time_before(seqp->ccid2s_sent,
 					   prev->ccid2s_sent));
 

@@ -562,8 +563,8 @@ static void ccid2_hc_tx_packet_recv(stru
 		hctx->ccid2hctx_rpseq = seqno;
 	} else {
 		/* check if packet is consecutive */
-		if ((hctx->ccid2hctx_rpseq + 1) = seqno)
-			hctx->ccid2hctx_rpseq++;
+		if (dccp_delta_seqno(hctx->ccid2hctx_rpseq, seqno) = 1)
+			hctx->ccid2hctx_rpseq = seqno;
 		/* it's a later packet */
 		else if (after48(seqno, hctx->ccid2hctx_rpseq)) {
 			hctx->ccid2hctx_rpdupack++;