dccp: fix bug in sequence number validation during connection setup

This fixes a bug in the sequence number validation during the initial handshake.

The code did not treat the initial sequence numbers ISS and ISR as read-only and
did not keep state for GSR and GSS as required by the specification. This causes
problems with retransmissions during the initial handshake, causing the
budding connection to be reset.

This patch now treats ISS/ISR as read-only and tracks GSS/GSR as required.

Signed-off-by: Samuel Jero <sj323707@ohio.edu>
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

4 files changed, 26 insertions, 18 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 1c67fe8..caf6e17 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -300,7 +300,8 @@ static void dccp_v4_err(struct sk_buff *skb, u32 info)
 		 */
 		WARN_ON(req->sk);
 
-		if (seq != dccp_rsk(req)->dreq_iss) {
+		if (!between48(seq, dccp_rsk(req)->dreq_iss,
+				    dccp_rsk(req)->dreq_gss)) {
 			NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);
 			goto out;
 		}
@@ -639,11 +640,12 @@ int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	 *
 	 * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
 	 *
-	 * In fact we defer setting S.GSR, S.SWL, S.SWH to
-	 * dccp_create_openreq_child.
+	 * Setting S.SWL/S.SWH to is deferred to dccp_create_openreq_child().
 	 */
 	dreq->dreq_isr	   = dcb->dccpd_seq;
+	dreq->dreq_gsr	   = dreq->dreq_isr;
 	dreq->dreq_iss	   = dccp_v4_init_sequence(skb);
+	dreq->dreq_gss     = dreq->dreq_iss;
 	dreq->dreq_service = service;
 
 	if (dccp_v4_send_response(sk, req, NULL))
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index ce903f7..4dc588f 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -193,7 +193,8 @@ static void dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		 */
 		WARN_ON(req->sk != NULL);
 
-		if (seq != dccp_rsk(req)->dreq_iss) {
+		if (!between48(seq, dccp_rsk(req)->dreq_iss,
+				    dccp_rsk(req)->dreq_gss)) {
 			NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);
 			goto out;
 		}
@@ -440,11 +441,12 @@ static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 	 *
 	 *   Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
 	 *
-	 *   In fact we defer setting S.GSR, S.SWL, S.SWH to
-	 *   dccp_create_openreq_child.
+	 * Setting S.SWL/S.SWH to is deferred to dccp_create_openreq_child().
 	 */
 	dreq->dreq_isr	   = dcb->dccpd_seq;
+	dreq->dreq_gsr     = dreq->dreq_isr;
 	dreq->dreq_iss	   = dccp_v6_init_sequence(skb);
+	dreq->dreq_gss     = dreq->dreq_iss;
 	dreq->dreq_service = service;
 
 	if (dccp_v6_send_response(sk, req, NULL))
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index 5a7f90b..ea850ce 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -127,9 +127,11 @@ struct sock *dccp_create_openreq_child(struct sock *sk,
 		 *    activation below, as these windows all depend on the local
 		 *    and remote Sequence Window feature values (7.5.2).
 		 */
-		newdp->dccps_gss = newdp->dccps_iss = dreq->dreq_iss;
+		newdp->dccps_iss = dreq->dreq_iss;
+		newdp->dccps_gss = dreq->dreq_gss;
 		newdp->dccps_gar = newdp->dccps_iss;
-		newdp->dccps_gsr = newdp->dccps_isr = dreq->dreq_isr;
+		newdp->dccps_isr = dreq->dreq_isr;
+		newdp->dccps_gsr = dreq->dreq_gsr;
 
 		/*
 		 * Activate features: initialise CCIDs, sequence windows etc.
@@ -164,9 +166,9 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
 	/* Check for retransmitted REQUEST */
 	if (dccp_hdr(skb)->dccph_type == DCCP_PKT_REQUEST) {
 
-		if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dreq->dreq_isr)) {
+		if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dreq->dreq_gsr)) {
 			dccp_pr_debug("Retransmitted REQUEST\n");
-			dreq->dreq_isr = DCCP_SKB_CB(skb)->dccpd_seq;
+			dreq->dreq_gsr = DCCP_SKB_CB(skb)->dccpd_seq;
 			/*
 			 * Send another RESPONSE packet
 			 * To protect against Request floods, increment retrans
@@ -186,12 +188,14 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
 		goto drop;
 
 	/* Invalid ACK */
-	if (DCCP_SKB_CB(skb)->dccpd_ack_seq != dreq->dreq_iss) {
+	if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
+				dreq->dreq_iss, dreq->dreq_gss)) {
 		dccp_pr_debug("Invalid ACK number: ack_seq=%llu, "
-			      "dreq_iss=%llu\n",
+			      "dreq_iss=%llu, dreq_gss=%llu\n",
 			      (unsigned long long)
 			      DCCP_SKB_CB(skb)->dccpd_ack_seq,
-			      (unsigned long long) dreq->dreq_iss);
+			      (unsigned long long) dreq->dreq_iss,
+			      (unsigned long long) dreq->dreq_gss);
 		goto drop;
 	}
 
diff --git a/net/dccp/output.c b/net/dccp/output.c
index dede3ed..7873673 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -408,10 +408,10 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
 	skb_dst_set(skb, dst_clone(dst));
 
 	dreq = dccp_rsk(req);
-	if (inet_rsk(req)->acked)	/* increase ISS upon retransmission */
-		dccp_inc_seqno(&dreq->dreq_iss);
+	if (inet_rsk(req)->acked)	/* increase GSS upon retransmission */
+		dccp_inc_seqno(&dreq->dreq_gss);
 	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
-	DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;
+	DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_gss;
 
 	/* Resolve feature dependencies resulting from choice of CCID */
 	if (dccp_feat_server_ccid_dependencies(dreq))
@@ -429,8 +429,8 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
 			   DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
 	dh->dccph_type	= DCCP_PKT_RESPONSE;
 	dh->dccph_x	= 1;
-	dccp_hdr_set_seq(dh, dreq->dreq_iss);
-	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
+	dccp_hdr_set_seq(dh, dreq->dreq_gss);
+	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_gsr);
 	dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;
 
 	dccp_csum_outgoing(skb);