mptcp: Handle incoming 32-bit DATA_FIN values

The peer may send a DATA_FIN mapping with either a 32-bit or 64-bit
sequence number. When a 32-bit sequence number is received for the
DATA_FIN, it must be expanded to 64 bits before comparing it to the
last acked sequence number. This expansion was missing.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/93
Fixes: 3721b9b646 ("mptcp: Track received DATA_FIN sequence number and add related helpers")
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/options.c

@@ -782,7 +782,7 @@ static void update_una(struct mptcp_sock *msk,
 	}
 }
 
-bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq)
+bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
 {
 	/* Skip if DATA_FIN was already received.
 	 * If updating simultaneously with the recvmsg loop, values
@@ -792,7 +792,8 @@ bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq)
 	if (READ_ONCE(msk->rcv_data_fin) || !READ_ONCE(msk->first))
 		return false;
 
-	WRITE_ONCE(msk->rcv_data_fin_seq, data_fin_seq);
+	WRITE_ONCE(msk->rcv_data_fin_seq,
+		   expand_ack(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
 	WRITE_ONCE(msk->rcv_data_fin, 1);
 
 	return true;
@@ -875,7 +876,7 @@ void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb,
 	 */
 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
 		if (mp_opt.data_fin && mp_opt.data_len == 1 &&
-		    mptcp_update_rcv_data_fin(msk, mp_opt.data_seq) &&
+		    mptcp_update_rcv_data_fin(msk, mp_opt.data_seq, mp_opt.dsn64) &&
 		    schedule_work(&msk->work))
 			sock_hold(subflow->conn);
 

net/mptcp/protocol.h

@@ -387,7 +387,7 @@ void mptcp_data_ready(struct sock *sk, struct sock *ssk);
 bool mptcp_finish_join(struct sock *sk);
 void mptcp_data_acked(struct sock *sk);
 void mptcp_subflow_eof(struct sock *sk);
-bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq);
+bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit);
 
 void __init mptcp_token_init(void);
 static inline void mptcp_token_init_request(struct request_sock *req)

net/mptcp/subflow.c

@@ -731,7 +731,8 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 
 	if (mpext->data_fin == 1) {
 		if (data_len == 1) {
-			bool updated = mptcp_update_rcv_data_fin(msk, mpext->data_seq);
+			bool updated = mptcp_update_rcv_data_fin(msk, mpext->data_seq,
+								 mpext->dsn64);
 			pr_debug("DATA_FIN with no payload seq=%llu", mpext->data_seq);
 			if (subflow->map_valid) {
 				/* A DATA_FIN might arrive in a DSS
@@ -748,8 +749,17 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 				return MAPPING_DATA_FIN;
 			}
 		} else {
-			mptcp_update_rcv_data_fin(msk, mpext->data_seq + data_len);
-			pr_debug("DATA_FIN with mapping seq=%llu", mpext->data_seq + data_len);
+			u64 data_fin_seq = mpext->data_seq + data_len;
+
+			/* If mpext->data_seq is a 32-bit value, data_fin_seq
+			 * must also be limited to 32 bits.
+			 */
+			if (!mpext->dsn64)
+				data_fin_seq &= GENMASK_ULL(31, 0);
+
+			mptcp_update_rcv_data_fin(msk, data_fin_seq, mpext->dsn64);
+			pr_debug("DATA_FIN with mapping seq=%llu dsn64=%d",
+				 data_fin_seq, mpext->dsn64);
 		}
 
 		/* Adjust for DATA_FIN using 1 byte of sequence space */