func (sshClient *sshClient) handleTCPChannel(
hostToConnect string,
portToConnect int,
newChannel ssh.NewChannel) {
if !sshClient.isPortForwardPermitted(
portToConnect,
sshClient.trafficRules.AllowTCPPorts,
sshClient.trafficRules.DenyTCPPorts) {
sshClient.rejectNewChannel(
newChannel, ssh.Prohibited, "port forward not permitted")
return
}
var bytesUp, bytesDown int64
sshClient.openedPortForward(sshClient.tcpTrafficState)
defer func() {
sshClient.closedPortForward(
sshClient.tcpTrafficState,
atomic.LoadInt64(&bytesUp),
atomic.LoadInt64(&bytesDown))
}()
// TOCTOU note: important to increment the port forward count (via
// openPortForward) _before_ checking isPortForwardLimitExceeded
// otherwise, the client could potentially consume excess resources
// by initiating many port forwards concurrently.
// TODO: close LRU connection (after successful Dial) instead of
// rejecting new connection?
if sshClient.isPortForwardLimitExceeded(
sshClient.tcpTrafficState,
sshClient.trafficRules.MaxTCPPortForwardCount) {
// Close the oldest TCP port forward. CloseOldest() closes
// the conn and the port forward's goroutine will complete
// the cleanup asynchronously.
//
// Some known limitations:
//
// - Since CloseOldest() closes the upstream socket but does not
// clean up all resources associated with the port forward. These
// include the goroutine(s) relaying traffic as well as the SSH
// channel. Closing the socket will interrupt the goroutines which
// will then complete the cleanup. But, since the full cleanup is
// asynchronous, there exists a possibility that a client can consume
// more than max port forward resources -- just not upstream sockets.
//
// - An LRU list entry for this port forward is not added until
// after the dial completes, but the port forward is counted
// towards max limits. This means many dials in progress will
// put established connections in jeopardy.
//
// - We're closing the oldest open connection _before_ successfully
// dialing the new port forward. This means we are potentially
// discarding a good connection to make way for a failed connection.
// We cannot simply dial first and still maintain a limit on
// resources used, so to address this we'd need to add some
// accounting for connections still establishing.
sshClient.tcpPortForwardLRU.CloseOldest()
log.WithContextFields(
LogFields{
"maxCount": sshClient.trafficRules.MaxTCPPortForwardCount,
}).Debug("closed LRU TCP port forward")
}
// Dial the target remote address. This is done in a goroutine to
// ensure the shutdown signal is handled immediately.
remoteAddr := fmt.Sprintf("%s:%d", hostToConnect, portToConnect)
log.WithContextFields(LogFields{"remoteAddr": remoteAddr}).Debug("dialing")
type dialTcpResult struct {
conn net.Conn
err error
}
resultChannel := make(chan *dialTcpResult, 1)
go func() {
// TODO: on EADDRNOTAVAIL, temporarily suspend new clients
// TODO: IPv6 support
conn, err := net.DialTimeout(
"tcp4", remoteAddr, SSH_TCP_PORT_FORWARD_DIAL_TIMEOUT)
resultChannel <- &dialTcpResult{conn, err}
}()
var result *dialTcpResult
select {
case result = <-resultChannel:
case <-sshClient.stopBroadcast:
// Note: may leave dial in progress
return
}
if result.err != nil {
sshClient.rejectNewChannel(newChannel, ssh.ConnectionFailed, result.err.Error())
return
}
// The upstream TCP port forward connection has been established. Schedule
// some cleanup and notify the SSH client that the channel is accepted.
fwdConn := result.conn
defer fwdConn.Close()
lruEntry := sshClient.tcpPortForwardLRU.Add(fwdConn)
defer lruEntry.Remove()
// ActivityMonitoredConn monitors the TCP port forward I/O and updates
// its LRU status. ActivityMonitoredConn also times out read on the port
// forward if both reads and writes have been idle for the specified
// duration.
fwdConn = psiphon.NewActivityMonitoredConn(
fwdConn,
time.Duration(sshClient.trafficRules.IdleTCPPortForwardTimeoutMilliseconds)*time.Millisecond,
true,
lruEntry)
fwdChannel, requests, err := newChannel.Accept()
if err != nil {
log.WithContextFields(LogFields{"error": err}).Warning("accept new channel failed")
return
}
go ssh.DiscardRequests(requests)
defer fwdChannel.Close()
log.WithContextFields(LogFields{"remoteAddr": remoteAddr}).Debug("relaying")
// Relay channel to forwarded connection.
// TODO: relay errors to fwdChannel.Stderr()?
relayWaitGroup := new(sync.WaitGroup)
relayWaitGroup.Add(1)
go func() {
defer relayWaitGroup.Done()
// io.Copy allocates a 32K temporary buffer, and each port forward relay uses
// two of these buffers; using io.CopyBuffer with a smaller buffer reduces the
// overall memory footprint.
bytes, err := io.CopyBuffer(
fwdChannel, fwdConn, make([]byte, SSH_TCP_PORT_FORWARD_COPY_BUFFER_SIZE))
atomic.AddInt64(&bytesDown, bytes)
if err != nil && err != io.EOF {
// Debug since errors such as "connection reset by peer" occur during normal operation
log.WithContextFields(LogFields{"error": err}).Debug("downstream TCP relay failed")
}
// Interrupt upstream io.Copy when downstream is shutting down.
// TODO: this is done to quickly cleanup the port forward when
// fwdConn has a read timeout, but is it clean -- upstream may still
// be flowing?
fwdChannel.Close()
}()
bytes, err := io.CopyBuffer(
fwdConn, fwdChannel, make([]byte, SSH_TCP_PORT_FORWARD_COPY_BUFFER_SIZE))
atomic.AddInt64(&bytesUp, bytes)
if err != nil && err != io.EOF {
log.WithContextFields(LogFields{"error": err}).Debug("upstream TCP relay failed")
}
// Shutdown special case: fwdChannel will be closed and return EOF when
// the SSH connection is closed, but we need to explicitly close fwdConn
// to interrupt the downstream io.Copy, which may be blocked on a
// fwdConn.Read().
fwdConn.Close()
relayWaitGroup.Wait()
log.WithContextFields(
LogFields{
"remoteAddr": remoteAddr,
"bytesUp": atomic.LoadInt64(&bytesUp),
"bytesDown": atomic.LoadInt64(&bytesDown)}).Debug("exiting")
}
func (mux *udpPortForwardMultiplexer) run() {
// In a loop, read udpgw messages from the client to this channel. Each message is
// a UDP packet to send upstream either via a new port forward, or on an existing
// port forward.
//
// A goroutine is run to read downstream packets for each UDP port forward. All read
// packets are encapsulated in udpgw protocol and sent down the channel to the client.
//
// When the client disconnects or the server shuts down, the channel will close and
// readUdpgwMessage will exit with EOF.
buffer := make([]byte, udpgwProtocolMaxMessageSize)
for {
// Note: message.packet points to the reusable memory in "buffer".
// Each readUdpgwMessage call will overwrite the last message.packet.
message, err := readUdpgwMessage(mux.sshChannel, buffer)
if err != nil {
if err != io.EOF {
log.WithContextFields(LogFields{"error": err}).Warning("readUpdgwMessage failed")
}
break
}
mux.portForwardsMutex.Lock()
portForward := mux.portForwards[message.connID]
mux.portForwardsMutex.Unlock()
if portForward != nil && message.discardExistingConn {
// The port forward's goroutine will complete cleanup, including
// tallying stats and calling sshClient.closedPortForward.
// portForward.conn.Close() will signal this shutdown.
// TODO: wait for goroutine to exit before proceeding?
portForward.conn.Close()
portForward = nil
}
if portForward != nil {
// Verify that portForward remote address matches latest message
if 0 != bytes.Compare(portForward.remoteIP, message.remoteIP) ||
portForward.remotePort != message.remotePort {
log.WithContext().Warning("UDP port forward remote address mismatch")
continue
}
} else {
// Create a new port forward
if !mux.sshClient.isPortForwardPermitted(
int(message.remotePort),
mux.sshClient.trafficRules.AllowUDPPorts,
mux.sshClient.trafficRules.DenyUDPPorts) {
// The udpgw protocol has no error response, so
// we just discard the message and read another.
continue
}
mux.sshClient.openedPortForward(mux.sshClient.udpTrafficState)
// Note: can't defer sshClient.closedPortForward() here
// TOCTOU note: important to increment the port forward count (via
// openPortForward) _before_ checking isPortForwardLimitExceeded
if mux.sshClient.isPortForwardLimitExceeded(
mux.sshClient.tcpTrafficState,
mux.sshClient.trafficRules.MaxUDPPortForwardCount) {
// Close the oldest UDP port forward. CloseOldest() closes
// the conn and the port forward's goroutine will complete
// the cleanup asynchronously.
//
// See LRU comment in handleTCPChannel() for a known
// limitations regarding CloseOldest().
mux.portForwardLRU.CloseOldest()
log.WithContextFields(
LogFields{
"maxCount": mux.sshClient.trafficRules.MaxUDPPortForwardCount,
}).Debug("closed LRU UDP port forward")
}
dialIP := net.IP(message.remoteIP)
dialPort := int(message.remotePort)
// Transparent DNS forwarding
if message.forwardDNS {
dialIP, dialPort = mux.transparentDNSAddress(dialIP, dialPort)
}
log.WithContextFields(
LogFields{
"remoteAddr": fmt.Sprintf("%s:%d", dialIP.String(), dialPort),
"connID": message.connID}).Debug("dialing")
// TODO: on EADDRNOTAVAIL, temporarily suspend new clients
udpConn, err := net.DialUDP(
"udp", nil, &net.UDPAddr{IP: dialIP, Port: dialPort})
if err != nil {
mux.sshClient.closedPortForward(mux.sshClient.udpTrafficState, 0, 0)
log.WithContextFields(LogFields{"error": err}).Warning("DialUDP failed")
continue
}
lruEntry := mux.portForwardLRU.Add(udpConn)
// ActivityMonitoredConn monitors the TCP port forward I/O and updates
// its LRU status. ActivityMonitoredConn also times out read on the port
// forward if both reads and writes have been idle for the specified
// duration.
conn := psiphon.NewActivityMonitoredConn(
udpConn,
time.Duration(mux.sshClient.trafficRules.IdleUDPPortForwardTimeoutMilliseconds)*time.Millisecond,
true,
lruEntry)
portForward = &udpPortForward{
connID: message.connID,
preambleSize: message.preambleSize,
remoteIP: message.remoteIP,
remotePort: message.remotePort,
conn: conn,
lruEntry: lruEntry,
bytesUp: 0,
bytesDown: 0,
mux: mux,
}
mux.portForwardsMutex.Lock()
mux.portForwards[portForward.connID] = portForward
mux.portForwardsMutex.Unlock()
// relayDownstream will call sshClient.closedPortForward()
mux.relayWaitGroup.Add(1)
go portForward.relayDownstream()
}
// Note: assumes UDP writes won't block (https://golang.org/pkg/net/#UDPConn.WriteToUDP)
_, err = portForward.conn.Write(message.packet)
if err != nil {
// Debug since errors such as "write: operation not permitted" occur during normal operation
log.WithContextFields(LogFields{"error": err}).Debug("upstream UDP relay failed")
// The port forward's goroutine will complete cleanup
portForward.conn.Close()
}
portForward.lruEntry.Touch()
atomic.AddInt64(&portForward.bytesUp, int64(len(message.packet)))
}
// Cleanup all UDP port forward workers when exiting
mux.portForwardsMutex.Lock()
for _, portForward := range mux.portForwards {
// The port forward's goroutine will complete cleanup
portForward.conn.Close()
}
mux.portForwardsMutex.Unlock()
mux.relayWaitGroup.Wait()
}
func (sshServer *sshServer) handleClient(tunnelProtocol string, clientConn net.Conn) {
sshServer.registerAcceptedClient(tunnelProtocol)
defer sshServer.unregisterAcceptedClient(tunnelProtocol)
geoIPData := sshServer.support.GeoIPService.Lookup(
psiphon.IPAddressFromAddr(clientConn.RemoteAddr()))
// TODO: apply reload of TrafficRulesSet to existing clients
sshClient := newSshClient(
sshServer,
tunnelProtocol,
geoIPData,
sshServer.support.TrafficRulesSet.GetTrafficRules(geoIPData.Country))
// Wrap the base client connection with an ActivityMonitoredConn which will
// terminate the connection if no data is received before the deadline. This
// timeout is in effect for the entire duration of the SSH connection. Clients
// must actively use the connection or send SSH keep alive requests to keep
// the connection active.
activityConn := psiphon.NewActivityMonitoredConn(
clientConn,
SSH_CONNECTION_READ_DEADLINE,
false,
nil)
clientConn = activityConn
// Further wrap the connection in a rate limiting ThrottledConn.
rateLimits := sshClient.trafficRules.GetRateLimits(tunnelProtocol)
clientConn = psiphon.NewThrottledConn(
clientConn,
rateLimits.DownstreamUnlimitedBytes,
int64(rateLimits.DownstreamBytesPerSecond),
rateLimits.UpstreamUnlimitedBytes,
int64(rateLimits.UpstreamBytesPerSecond))
// Run the initial [obfuscated] SSH handshake in a goroutine so we can both
// respect shutdownBroadcast and implement a specific handshake timeout.
// The timeout is to reclaim network resources in case the handshake takes
// too long.
type sshNewServerConnResult struct {
conn net.Conn
sshConn *ssh.ServerConn
channels <-chan ssh.NewChannel
requests <-chan *ssh.Request
err error
}
resultChannel := make(chan *sshNewServerConnResult, 2)
if SSH_HANDSHAKE_TIMEOUT > 0 {
time.AfterFunc(time.Duration(SSH_HANDSHAKE_TIMEOUT), func() {
resultChannel <- &sshNewServerConnResult{err: errors.New("ssh handshake timeout")}
})
}
go func(conn net.Conn) {
sshServerConfig := &ssh.ServerConfig{
PasswordCallback: sshClient.passwordCallback,
AuthLogCallback: sshClient.authLogCallback,
ServerVersion: sshServer.support.Config.SSHServerVersion,
}
sshServerConfig.AddHostKey(sshServer.sshHostKey)
result := &sshNewServerConnResult{}
// Wrap the connection in an SSH deobfuscator when required.
if psiphon.TunnelProtocolUsesObfuscatedSSH(tunnelProtocol) {
// Note: NewObfuscatedSshConn blocks on network I/O
// TODO: ensure this won't block shutdown
conn, result.err = psiphon.NewObfuscatedSshConn(
psiphon.OBFUSCATION_CONN_MODE_SERVER,
clientConn,
sshServer.support.Config.ObfuscatedSSHKey)
if result.err != nil {
result.err = psiphon.ContextError(result.err)
}
}
if result.err == nil {
result.sshConn, result.channels, result.requests, result.err =
ssh.NewServerConn(conn, sshServerConfig)
}
resultChannel <- result
}(clientConn)
var result *sshNewServerConnResult
select {
case result = <-resultChannel:
case <-sshServer.shutdownBroadcast:
// Close() will interrupt an ongoing handshake
// TODO: wait for goroutine to exit before returning?
clientConn.Close()
return
}
if result.err != nil {
clientConn.Close()
// This is a Debug log due to noise. The handshake often fails due to I/O
// errors as clients frequently interrupt connections in progress when
// client-side load balancing completes a connection to a different server.
log.WithContextFields(LogFields{"error": result.err}).Debug("handshake failed")
return
}
sshClient.Lock()
sshClient.sshConn = result.sshConn
sshClient.activityConn = activityConn
sshClient.Unlock()
clientID, ok := sshServer.registerEstablishedClient(sshClient)
if !ok {
clientConn.Close()
log.WithContext().Warning("register failed")
return
}
defer sshServer.unregisterEstablishedClient(clientID)
sshClient.runClient(result.channels, result.requests)
// Note: sshServer.unregisterClient calls sshClient.Close(),
// which also closes underlying transport Conn.
}