tipc: add SYN bit to connection setup messages

Messages intended for intitating a connection are currently
indistinguishable from regular datagram messages. The TIPC
protocol specification defines bit 17 in word 0 as a SYN bit
to allow sanity check of such messages in the listening socket,
but this has so far never been implemented.

We do that in this commit.
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/msg.h

@@ -216,6 +216,16 @@ static inline void msg_set_non_seq(struct tipc_msg *m, u32 n)
 	msg_set_bits(m, 0, 20, 1, n);
 }
 
+static inline int msg_is_syn(struct tipc_msg *m)
+{
+	return msg_bits(m, 0, 17, 1);
+}
+
+static inline void msg_set_syn(struct tipc_msg *m, u32 d)
+{
+	msg_set_bits(m, 0, 17, 1, d);
+}
+
 static inline int msg_dest_droppable(struct tipc_msg *m)
 {
 	return msg_bits(m, 0, 19, 1);

net/tipc/node.h

@@ -45,6 +45,7 @@
 /* Optional capabilities supported by this code version
  */
 enum {
+	TIPC_SYN_BIT          = (1),
 	TIPC_BCAST_SYNCH      = (1 << 1),
 	TIPC_BCAST_STATE_NACK = (1 << 2),
 	TIPC_BLOCK_FLOWCTL    = (1 << 3),
@@ -53,7 +54,8 @@ enum {
 	TIPC_LINK_PROTO_SEQNO = (1 << 6)
 };
 
-#define TIPC_NODE_CAPABILITIES (TIPC_BCAST_SYNCH       |  \
+#define TIPC_NODE_CAPABILITIES (TIPC_SYN_BIT           |  \
+				TIPC_BCAST_SYNCH       |   \
 				TIPC_BCAST_STATE_NACK  |   \
 				TIPC_BCAST_RCAST       |   \
 				TIPC_BLOCK_FLOWCTL     |   \

net/tipc/socket.c

@@ -1319,6 +1319,7 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dlen)
 			tsk->conn_type = dest->addr.name.name.type;
 			tsk->conn_instance = dest->addr.name.name.instance;
 		}
+		msg_set_syn(hdr, 1);
 	}
 
 	seq = &dest->addr.nameseq;
@@ -1478,6 +1479,7 @@ static void tipc_sk_finish_conn(struct tipc_sock *tsk, u32 peer_port,
 	struct net *net = sock_net(sk);
 	struct tipc_msg *msg = &tsk->phdr;
 
+	msg_set_syn(msg, 0);
 	msg_set_destnode(msg, peer_node);
 	msg_set_destport(msg, peer_port);
 	msg_set_type(msg, TIPC_CONN_MSG);
@@ -2006,6 +2008,9 @@ static bool tipc_sk_filter_connect(struct tipc_sock *tsk, struct sk_buff *skb)
 		return false;
 	case TIPC_LISTEN:
 		/* Accept only SYN message */
+		if (!msg_is_syn(hdr) &&
+		    tipc_node_get_capabilities(net, onode) & TIPC_SYN_BIT)
+			return false;
 		if (!con_msg && !err)
 			return true;
 		return false;