peer: Synchronize net.Conn with a mutex

The access guarded by an atomic int32 was incorrect.  For example, access to
the p.conn could be performed as long as p.connected was non-zero, but
p.connected would be incremented before p.conn was ever assigned by
AssociateConnection.

While here, also add missing mutex locking protecting timeConnected and na.

peer/peer.go

@@ -460,10 +460,10 @@ type Peer struct {
 	bytesSent     uint64
 	lastRecv      int64
 	lastSend      int64
-	connected     int32
 	disconnect    int32
 
-	conn net.Conn
+	conn    net.Conn
+	connMtx sync.Mutex
 
 	// blake256Hasher is the hash.Hash object that is used by readMessage
 	// to calculate the hash of read mixing messages.  Every peer's hasher
@@ -1918,23 +1918,27 @@ func (p *Peer) QueueInventoryImmediate(invVect *wire.InvVect) {
 //
 // This function is safe for concurrent access.
 func (p *Peer) Connected() bool {
-	return atomic.LoadInt32(&p.connected) != 0 &&
-		atomic.LoadInt32(&p.disconnect) == 0
+	p.connMtx.Lock()
+	defer p.connMtx.Unlock()
+
+	return p.conn != nil && atomic.LoadInt32(&p.disconnect) == 0
 }
 
 // Disconnect disconnects the peer by closing the connection.  Calling this
 // function when the peer is already disconnected or in the process of
 // disconnecting will have no effect.
 func (p *Peer) Disconnect() {
-	if atomic.AddInt32(&p.disconnect, 1) != 1 {
-		return
-	}
+	p.connMtx.Lock()
+	defer p.connMtx.Unlock()
 
 	log.Tracef("Disconnecting %s", p)
-	if atomic.LoadInt32(&p.connected) != 0 {
+	if p.conn != nil {
 		p.conn.Close()
 	}
-	close(p.quit)
+
+	if atomic.CompareAndSwapInt32(&p.disconnect, 0, 1) {
+		close(p.quit)
+	}
 }
 
 // readRemoteVersionMsg waits for the next message to arrive from the remote
@@ -2146,13 +2150,20 @@ func (p *Peer) start() error {
 // Calling this function when the peer is already connected will
 // have no effect.
 func (p *Peer) AssociateConnection(conn net.Conn) {
+	p.connMtx.Lock()
+
 	// Already connected?
-	if !atomic.CompareAndSwapInt32(&p.connected, 0, 1) {
+	if p.conn != nil {
+		p.connMtx.Unlock()
 		return
 	}
 
 	p.conn = conn
+	p.connMtx.Unlock()
+
+	p.statsMtx.Lock()
 	p.timeConnected = time.Now()
+	p.statsMtx.Unlock()
 
 	if p.inbound {
 		p.addr = p.conn.RemoteAddr().String()
@@ -2166,7 +2177,9 @@ func (p *Peer) AssociateConnection(conn net.Conn) {
 			p.Disconnect()
 			return
 		}
+		p.flagsMtx.Lock()
 		p.na = na
+		p.flagsMtx.Unlock()
 	}
 
 	go func(peer *Peer) {