Implement proxied connections

The feature is implemented as follows:
- when creating a host, there is a possiblity to add a "hop"
- hops are referend them with the name of the host in sshportal
- the hop ID is then saved in the DB in the hosts table
- when connecting to a host, sshportal will recurse through all the
  possible hops of a host (allowing chained proxies)

db.go

@@ -63,6 +63,8 @@ type Host struct {
 	HostKey  []byte       `sql:"size:10000" valid:"optional"`
 	Groups   []*HostGroup `gorm:"many2many:host_host_groups;"`
 	Comment  string       `valid:"optional"`
+	Hop      *Host
+	HopID    uint
 }
 
 // UserKey defines a user public key used by sshportal to identify the user

dbinit.go

@@ -458,6 +458,30 @@ func dbInit(db *gorm.DB) error {
 			Rollback: func(tx *gorm.DB) error {
 				return fmt.Errorf("not implemented")
 			},
+		}, {
+			ID: "29",
+			Migrate: func(tx *gorm.DB) error {
+				type Host struct {
+					// FIXME: use uuid for ID
+					gorm.Model
+					Name     string `gorm:"size:32"`
+					Addr     string
+					User     string
+					Password string
+					URL      string
+					SSHKey   *SSHKey      `gorm:"ForeignKey:SSHKeyID"`
+					SSHKeyID uint         `gorm:"index"`
+					HostKey  []byte       `sql:"size:10000"`
+					Groups   []*HostGroup `gorm:"many2many:host_host_groups;"`
+					Comment  string
+					Hop      *Host
+					HopID    uint
+				}
+				return tx.AutoMigrate(&Host{}).Error
+			},
+			Rollback: func(tx *gorm.DB) error {
+				return fmt.Errorf("not implemented")
+			},
 		},
 	})
 	if err := m.Migrate(); err != nil {

pkg/bastionsession/bastionsession.go

@@ -3,13 +3,13 @@ package bastionsession
 import (
 	"errors"
 	"io"
+	"log"
+	"os"
 	"strings"
 	"time"
-	"os"
-	"log"
 
-	"github.com/gliderlabs/ssh"
 	"github.com/arkan/bastion/pkg/logchannel"
+	"github.com/gliderlabs/ssh"
 	gossh "golang.org/x/crypto/ssh"
 )
 
@@ -19,7 +19,7 @@ type Config struct {
 	ClientConfig *gossh.ClientConfig
 }
 
-func ChannelHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewChannel, ctx ssh.Context, config Config) error {
+func MultiChannelHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewChannel, ctx ssh.Context, configs []Config) error {
 	if newChan.ChannelType() != "session" {
 		newChan.Reject(gossh.UnknownChannelType, "unsupported channel type")
 		return nil
@@ -31,19 +31,37 @@ func ChannelHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewCh
 		return nil
 	}
 
-	// open client channel
+	var lastClient *gossh.Client
-	rconn, err := gossh.Dial("tcp", config.Addr, config.ClientConfig)
+
-	if err != nil {
+    // go through all the hops
-		return err
+	for _, config := range configs {
+		var client *gossh.Client
+		if lastClient == nil {
+			client, err = gossh.Dial("tcp", config.Addr, config.ClientConfig)
+		} else {
+			rconn, err := lastClient.Dial("tcp", config.Addr)
+			if err != nil {
+				return err
+			}
+			ncc, chans, reqs, err := gossh.NewClientConn(rconn, config.Addr, config.ClientConfig)
+			if err != nil {
+				return err
+			}
+			client = gossh.NewClient(ncc, chans, reqs)
+		}
+		if err != nil {
+			return err
+		}
+		defer func() { _ = client.Close() }()
+		lastClient = client
 	}
-	defer func() { _ = rconn.Close() }()
+	rch, rreqs, err := lastClient.OpenChannel("session", []byte{})
-	rch, rreqs, err := rconn.OpenChannel("session", []byte{})
 	if err != nil {
 		return err
 	}
 	user := conn.User()
 	// pipe everything
-	return pipe(lreqs, rreqs, lch, rch, config.Logs, user)
+	return pipe(lreqs, rreqs, lch, rch, configs[len(configs)-1].Logs, user)
 }
 
 func pipe(lreqs, rreqs <-chan *gossh.Request, lch, rch gossh.Channel, logsLocation string, user string) error {

shell.go

@@ -642,6 +642,7 @@ GLOBAL OPTIONS:
 						cli.StringFlag{Name: "password, p", Usage: "If present, sshportal will use password-based authentication"},
 						cli.StringFlag{Name: "comment, c"},
 						cli.StringFlag{Name: "key, k", Usage: "`KEY` to use for authentication"},
+						cli.StringFlag{Name: "hop, o", Usage: "Hop to use for connecting to the server"},
 						cli.StringSliceFlag{Name: "group, g", Usage: "Assigns the host to `HOSTGROUPS` (default: \"default\")"},
 					},
 					Action: func(c *cli.Context) error {
@@ -665,7 +666,13 @@ GLOBAL OPTIONS:
 							host.Password = c.String("password")
 						}
 						host.Name = strings.Split(host.Hostname(), ".")[0]
-
+						if c.String("hop") != "" {
+							hop, err := HostByName(db, c.String("hop"))
+							if err != nil {
+								return err
+							}
+							host.Hop = hop
+						}
 						if c.String("name") != "" {
 							host.Name = c.String("name")
 						}
@@ -776,7 +783,7 @@ GLOBAL OPTIONS:
 						}
 
 						table := tablewriter.NewWriter(s)
-						table.SetHeader([]string{"ID", "Name", "URL", "Key", "Groups", "Updated", "Created", "Comment"})
+						table.SetHeader([]string{"ID", "Name", "URL", "Key", "Groups", "Updated", "Created", "Comment", "Hop"})
 						table.SetBorder(false)
 						table.SetCaption(true, fmt.Sprintf("Total: %d hosts.", len(hosts)))
 						for _, host := range hosts {
@@ -790,6 +797,14 @@ GLOBAL OPTIONS:
 							for _, hostGroup := range host.Groups {
 								groupNames = append(groupNames, hostGroup.Name)
 							}
+							var hop string
+							if host.HopID != 0 {
+								var hopHost Host
+								db.Model(&host).Related(&hopHost, "HopID")
+								hop = hopHost.Name
+							} else {
+								hop = ""
+							}
 							table.Append([]string{
 								fmt.Sprintf("%d", host.ID),
 								host.Name,
@@ -799,6 +814,7 @@ GLOBAL OPTIONS:
 								humanize.Time(host.UpdatedAt),
 								humanize.Time(host.CreatedAt),
 								host.Comment,
+								hop,
 								//FIXME: add some stats about last access time etc
 							})
 						}

ssh.go

@@ -113,16 +113,33 @@ func channelHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewCh
 
 		switch host.Scheme() {
 		case BastionSchemeSSH:
-			clientConfig, err := bastionClientConfig(ctx, host)
+			sessionConfigs := make([]bastionsession.Config, 0)
-			if err != nil {
+			currentHost := host
-				ch, _, err2 := newChan.Accept()
+			for currentHost != nil {
+				clientConfig, err2 := bastionClientConfig(ctx, currentHost)
 				if err2 != nil {
+					ch, _, err3 := newChan.Accept()
+					if err3 != nil {
+						return
+					}
+					fmt.Fprintf(ch, "error: %v\n", err2)
+					// FIXME: force close all channels
+					_ = ch.Close()
 					return
 				}
-				fmt.Fprintf(ch, "error: %v\n", err)
+				sessionConfigs = append([]bastionsession.Config{{
-				// FIXME: force close all channels
+					Addr:         currentHost.DialAddr(),
-				_ = ch.Close()
+					ClientConfig: clientConfig,
-				return
+					Logs:         actx.config.logsLocation,
+				}}, sessionConfigs...)
+				if currentHost.HopID != 0 {
+					var newHost Host
+					actx.db.Model(currentHost).Related(&newHost, "HopID")
+					hostname := newHost.Name
+					currentHost, _ = HostByName(actx.db, hostname)
+				} else {
+					currentHost = nil
+				}
 			}
 
 			sess := Session{
@@ -140,11 +157,7 @@ func channelHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewCh
 				return
 			}
 
-			err = bastionsession.ChannelHandler(srv, conn, newChan, ctx, bastionsession.Config{
+			err = bastionsession.MultiChannelHandler(srv, conn, newChan, ctx, sessionConfigs)
-				Addr:         host.DialAddr(),
-				ClientConfig: clientConfig,
-				Logs:         actx.config.logsLocation,
-			})
 
 			now := time.Now()
 			sessUpdate := Session{