1// SFTP server for users with Flounder accounts
  2// 	A lot of this is copied from SFTPGo, but simplified for our use case.
  3package main
  4
  5import (
  6	"fmt"
  7	"io"
  8	"io/ioutil"
  9	"log"
 10	"net"
 11	"os"
 12	"path"
 13	"path/filepath"
 14	"runtime/debug"
 15	"strings"
 16	"time"
 17
 18	"github.com/pkg/sftp"
 19	"golang.org/x/crypto/ssh"
 20)
 21
 22type Connection struct {
 23	User string
 24}
 25
 26func (con *Connection) Fileread(request *sftp.Request) (io.ReaderAt, error) {
 27	// check user perms -- cant read others hidden files
 28	fullpath := path.Join(c.FilesDirectory, filepath.Clean(request.Filepath))
 29	f, err := os.OpenFile(fullpath, os.O_RDONLY, 0)
 30	if err != nil {
 31		return nil, err
 32	}
 33	return f, nil
 34}
 35
 36func (con *Connection) Filewrite(request *sftp.Request) (io.WriterAt, error) {
 37	// check user perms -- cant write others files
 38	fullpath := path.Join(c.FilesDirectory, filepath.Clean(request.Filepath))
 39	userDir := getUserDirectory(con.User) // NOTE -- not cross platform
 40	if strings.HasPrefix(fullpath, userDir) {
 41		f, err := os.OpenFile(fullpath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
 42		if err != nil {
 43			return nil, err
 44		}
 45		return f, nil
 46	} else {
 47		return nil, fmt.Errorf("Invalid permissions")
 48	}
 49}
 50
 51func (conn *Connection) Filelist(request *sftp.Request) (sftp.ListerAt, error) {
 52	fullpath := path.Join(c.FilesDirectory, filepath.Clean(request.Filepath))
 53	switch request.Method {
 54	case "List":
 55		f, err := os.Open(fullpath)
 56		if err != nil {
 57			return nil, err
 58		}
 59		fileInfo, err := f.Readdir(-1)
 60		if err != nil {
 61			return nil, err
 62		}
 63		return listerat(fileInfo), nil
 64	case "Stat":
 65		stat, err := os.Stat(fullpath)
 66		if err != nil {
 67			return nil, err
 68		}
 69		return listerat([]os.FileInfo{stat}), nil
 70	}
 71	return nil, fmt.Errorf("Invalid command")
 72}
 73
 74func (c *Connection) Filecmd(request *sftp.Request) error {
 75	// remove, rename, setstat? find out
 76	return nil
 77}
 78
 79// TODO hide hidden folders
 80// Users have write persm on their files, read perms on all
 81
 82func buildHandlers(connection *Connection) sftp.Handlers {
 83	return sftp.Handlers{
 84		connection,
 85		connection,
 86		connection,
 87		connection,
 88	}
 89}
 90
 91// Based on example server code from golang.org/x/crypto/ssh and server_standalone
 92func runSFTPServer() {
 93
 94	// An SSH server is represented by a ServerConfig, which holds
 95	// certificate details and handles authentication of ServerConns.
 96	config := &ssh.ServerConfig{
 97		PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
 98			// Should use constant-time compare (or better, salt+hash) in
 99			// a production setting.
100			if isOkUsername(c.User()) != nil { // extra check, probably unnecessary
101				return nil, fmt.Errorf("Invalid username")
102			}
103			_, _, err := checkLogin(c.User(), string(pass))
104			// TODO maybe give admin extra permissions?
105			if err != nil {
106				return nil, fmt.Errorf("password rejected for %q", c.User())
107			} else {
108				log.Printf("Login: %s\n", c.User())
109				return nil, nil
110			}
111		},
112	}
113
114	// TODO generate key automatically
115	privateBytes, err := ioutil.ReadFile("id_rsa")
116	if err != nil {
117		log.Fatal("Failed to load private key", err)
118	}
119
120	private, err := ssh.ParsePrivateKey(privateBytes)
121	if err != nil {
122		log.Fatal("Failed to parse private key", err)
123	}
124
125	config.AddHostKey(private)
126
127	listener, err := net.Listen("tcp", "0.0.0.0:2024")
128	if err != nil {
129		log.Fatal("failed to listen for connection", err)
130	}
131
132	fmt.Printf("Listening on %v\n", listener.Addr())
133
134	for {
135		conn, err := listener.Accept()
136		if err != nil {
137			log.Fatal(err)
138		}
139		go acceptInboundConnection(conn, config)
140	}
141}
142
143func acceptInboundConnection(conn net.Conn, config *ssh.ServerConfig) {
144	defer func() {
145		if r := recover(); r != nil {
146			log.Println("panic in AcceptInboundConnection: %#v stack strace: %v", r, string(debug.Stack()))
147		}
148	}()
149	ipAddr := GetIPFromRemoteAddress(conn.RemoteAddr().String())
150	fmt.Println("Request from IP " + ipAddr)
151	limiter := getVisitor(ipAddr)
152	if limiter.Allow() == false {
153		conn.Close()
154		return
155	}
156	// Before beginning a handshake must be performed on the incoming net.Conn
157	// we'll set a Deadline for handshake to complete, the default is 2 minutes as OpenSSH
158	conn.SetDeadline(time.Now().Add(2 * time.Minute))
159
160	// Before use, a handshake must be performed on the incoming net.Conn.
161	sconn, chans, reqs, err := ssh.NewServerConn(conn, config)
162	if err != nil {
163		log.Printf("failed to accept an incoming connection: %v", err)
164		return
165	}
166	log.Println("login detected:", sconn.User())
167	fmt.Fprintf(os.Stderr, "SSH server established\n")
168	// handshake completed so remove the deadline, we'll use IdleTimeout configuration from now on
169	conn.SetDeadline(time.Time{})
170
171	defer conn.Close()
172
173	// The incoming Request channel must be serviced.
174	go ssh.DiscardRequests(reqs)
175
176	// Service the incoming Channel channel.
177	channelCounter := int64(0)
178	for newChannel := range chans {
179		// Channels have a type, depending on the application level
180		// protocol intended. In the case of an SFTP session, this is "subsystem"
181		// with a payload string of "<length=4>sftp"
182		fmt.Fprintf(os.Stderr, "Incoming channel: %s\n", newChannel.ChannelType())
183		if newChannel.ChannelType() != "session" {
184			newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
185			fmt.Fprintf(os.Stderr, "Unknown channel type: %s\n", newChannel.ChannelType())
186			continue
187		}
188		channel, requests, err := newChannel.Accept()
189		if err != nil {
190			log.Println("could not accept channel.", err)
191			continue
192		}
193
194		channelCounter++
195		fmt.Fprintf(os.Stderr, "Channel accepted\n")
196
197		// Sessions have out-of-band requests such as "shell",
198		// "pty-req" and "env".  Here we handle only the
199		// "subsystem" request.
200		go func(in <-chan *ssh.Request) {
201			for req := range in {
202				fmt.Fprintf(os.Stderr, "Request: %v\n", req.Type)
203				ok := false
204				switch req.Type {
205				case "subsystem":
206					fmt.Fprintf(os.Stderr, "Subsystem: %s\n", req.Payload[4:])
207					if string(req.Payload[4:]) == "sftp" {
208						ok = true
209					}
210				}
211				fmt.Fprintf(os.Stderr, " - accepted: %v\n", ok)
212				req.Reply(ok, nil)
213			}
214		}(requests)
215		connection := Connection{sconn.User()}
216		root := buildHandlers(&connection)
217		server := sftp.NewRequestServer(channel, root)
218		if err := server.Serve(); err == io.EOF {
219			server.Close()
220			log.Println("sftp client exited session.")
221		} else if err != nil {
222			log.Println("sftp server completed with error:", err)
223			return
224		}
225	}
226}
227
228type listerat []os.FileInfo
229
230// Modeled after strings.Reader's ReadAt() implementation
231func (f listerat) ListAt(ls []os.FileInfo, offset int64) (int, error) {
232	var n int
233	if offset >= int64(len(f)) {
234		return 0, io.EOF
235	}
236	n = copy(ls, f[offset:])
237	if n < len(ls) {
238		return n, io.EOF
239	}
240	return n, nil
241}