135 lines
3.7 KiB
Go
135 lines
3.7 KiB
Go
package sshrpc
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import (
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"fmt"
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"log"
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"net"
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"net/rpc"
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"golang.org/x/crypto/ssh"
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)
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// DefaultRPCChannel is the Channel Name that will be used to carry the RPC traffic, can be changed in Serverr and Client
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const DefaultRPCChannel = "RPCChannel"
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// RPCSubsystem is the subsystem that will be used to trigger RPC endpoint creation
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const RPCSubsystem = "RPCSubsystem"
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// Server represents an SSH Server that spins up RPC servers when requested.
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type Server struct {
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*rpc.Server
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Config *ssh.ServerConfig
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ChannelName string
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RPCClient *rpc.Client
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sshConn ssh.Conn
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}
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// NewServer returns a new Server to handle incoming SSH and RPC requests.
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func NewServer() *Server {
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c := &ssh.ServerConfig{
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PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
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if c.User() == "sshrpc" && string(pass) == "sshrpc" {
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return nil, nil
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}
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return nil, fmt.Errorf("password rejected for %q", c.User())
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},
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}
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return &Server{rpc.NewServer(), c, DefaultRPCChannel, nil, nil}
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}
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// StartServer starts the server listening for requests
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func (s *Server) StartServer(address string) {
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// Once a ServerConfig has been configured, connections can be accepted.
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listener, err := net.Listen("tcp", address)
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if err != nil {
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log.Fatal("failed to listen on ", address)
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}
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// Accept all connections
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log.Print("listening on ", address)
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for {
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tcpConn, err := listener.Accept()
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if err != nil {
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log.Printf("failed to accept incoming connection (%s)", err)
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continue
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}
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// Before use, a handshake must be performed on the incoming net.Conn.
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sshConn, chans, reqs, err := ssh.NewServerConn(tcpConn, s.Config)
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s.sshConn = sshConn
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if err != nil {
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log.Printf("failed to handshake (%s)", err)
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continue
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}
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log.Printf("new ssh connection from %s (%s)", sshConn.RemoteAddr(), sshConn.ClientVersion())
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// Print incoming out-of-band Requests
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go s.handleRequests(reqs)
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// Accept all channels
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go s.handleChannels(chans)
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}
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}
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// handleRequests handles global out-of-band SSH Requests
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func (s *Server) handleRequests(reqs <-chan *ssh.Request) {
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for req := range reqs {
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log.Printf("recieved out-of-band request: %+v", req)
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}
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}
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// handleChannels handels SSH Channel requests and their local out-of-band SSH Requests
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func (s *Server) handleChannels(chans <-chan ssh.NewChannel) {
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// Service the incoming Channel channel.
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for newChannel := range chans {
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log.Printf("Received channel: %v", newChannel.ChannelType())
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// Check the type of channel
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if t := newChannel.ChannelType(); t != s.ChannelName {
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newChannel.Reject(ssh.UnknownChannelType, fmt.Sprintf("unknown channel type: %s", t))
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continue
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}
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channel, requests, err := newChannel.Accept()
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if err != nil {
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log.Printf("could not accept channel (%s)", err)
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continue
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}
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log.Printf("Accepted channel")
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// Channels can have out-of-band requests
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go func(in <-chan *ssh.Request) {
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for req := range in {
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ok := false
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switch req.Type {
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case "subsystem":
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ok = true
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log.Printf("subsystem '%s'", req.Payload)
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switch string(req.Payload[4:]) {
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//RPCSubsystem Request made indicates client desires RPC Server access
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case RPCSubsystem:
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go s.ServeConn(channel)
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log.Printf("Started SSH RPC")
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// triggers reverse RPC connection as well
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clientChannel, err := openRPCClientChannel(s.sshConn, s.ChannelName+"-reverse")
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if err != nil {
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log.Printf("Failed to create client channel: " + err.Error())
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continue
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}
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s.RPCClient = rpc.NewClient(clientChannel)
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log.Printf("Started SSH RPC client")
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default:
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log.Printf("Unknown subsystem: %s", req.Payload)
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}
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}
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if !ok {
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log.Printf("declining %s request...", req.Type)
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}
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req.Reply(ok, nil)
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}
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}(requests)
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}
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}
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