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ssh.go
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ssh.go
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package main
import (
"bufio"
"fmt"
"github.com/gliderlabs/ssh"
"github.com/jonasbak/yasp/utils"
gossh "golang.org/x/crypto/ssh"
"io/ioutil"
"log"
"os"
"sync"
"unicode"
)
const (
forwardedTCPChannelType = "forwarded-tcpip"
)
type remoteForwardRequest struct {
BindAddr string
BindPort uint32
}
type remoteForwardSuccess struct {
BindPort uint32
}
type remoteForwardCancelRequest struct {
BindAddr string
BindPort uint32
}
type remoteForwardChannelData struct {
DestAddr string
DestPort uint32
OriginAddr string
OriginPort uint32
}
type session struct {
conn *gossh.ServerConn
pipeR *os.File
pipeW *os.File
settings utils.SessionSettings
errors []error
}
func (s *session) pushError(err error) {
s.errors = append(s.errors, err)
}
type forwardedTCPHandler struct {
sync.Mutex
sessions map[string]*session
subdomains map[string]string
onCreate map[string]chan struct{}
}
func (h *forwardedTCPHandler) HandleSSHRequest(ctx ssh.Context, srv *ssh.Server, req *gossh.Request) (bool, []byte) {
sessionID := ctx.SessionID()
h.Lock()
if h.sessions == nil {
h.sessions = make(map[string]*session)
}
if h.subdomains == nil {
h.subdomains = make(map[string]string)
}
if h.onCreate == nil {
h.onCreate = make(map[string]chan struct{})
}
onCreate, ok := h.onCreate[sessionID]
if !ok {
onCreate = make(chan struct{})
h.onCreate[sessionID] = onCreate
}
h.Unlock()
defer func() { onCreate <- struct{}{} }()
conn := ctx.Value(ssh.ContextKeyConn).(*gossh.ServerConn)
switch req.Type {
case "tcpip-forward":
var reqPayload remoteForwardRequest
if err := gossh.Unmarshal(req.Payload, &reqPayload); err != nil {
// TODO: log parse failure
return false, []byte{}
}
subdomain := reqPayload.BindAddr
pipeR, pipeW, _ := os.Pipe()
settings := utils.DefaultSettingsWithSubdomain(subdomain)
go func() {
<-ctx.Done()
h.Lock()
session, ok := h.sessions[sessionID]
if ok {
session.pipeR.Close()
session.pipeW.Close()
delete(h.sessions, sessionID)
delete(h.onCreate, sessionID)
subdomainSession, ok := h.subdomains[session.settings.Subdomain]
if ok && subdomainSession == sessionID {
delete(h.subdomains, session.settings.Subdomain)
}
}
log.Printf("cleaned up after %s", sessionID)
h.Unlock()
}()
h.Lock()
defer h.Unlock()
s := session{
conn,
pipeR,
pipeW,
settings,
[]error{},
}
h.sessions[sessionID] = &s
if err := h.ReversePortForwardingCallback(ctx, subdomain, reqPayload.BindPort); err != nil {
s.pushError(err)
return false, []byte("port forwarding failed")
}
h.subdomains[subdomain] = sessionID
return true, gossh.Marshal(&remoteForwardSuccess{reqPayload.BindPort})
case "cancel-tcpip-forward":
var reqPayload remoteForwardCancelRequest
if err := gossh.Unmarshal(req.Payload, &reqPayload); err != nil {
// TODO: log parse failure
return false, []byte{}
}
h.Lock()
session, ok := h.sessions[sessionID]
if ok {
session.pipeR.Close()
session.pipeW.Close()
delete(h.sessions, sessionID)
delete(h.onCreate, sessionID)
subdomainSession, ok := h.subdomains[session.settings.Subdomain]
if ok && subdomainSession == sessionID {
delete(h.subdomains, session.settings.Subdomain)
}
}
h.Unlock()
return true, nil
default:
return false, nil
}
}
func (h *forwardedTCPHandler) ReversePortForwardingCallback(ctx ssh.Context, subdomain string, port uint32) error {
if port != 80 {
return fmt.Errorf("Port must be 80 for http forwarding")
}
for _, r := range subdomain {
if !unicode.IsLetter(r) {
return fmt.Errorf("Subdomain can only contain letters")
}
}
_, exists := h.subdomains[subdomain]
if exists {
return fmt.Errorf("Subdomain '%s' already taken", subdomain)
}
return nil
}
func getPublicKeyHandler() ssh.PublicKeyHandler {
authorizedKeysDir := os.Getenv("AUTHORIZED_KEYS_DIR")
if authorizedKeysDir == "" {
return nil
}
authorizedKeysFiles, err := ioutil.ReadDir(authorizedKeysDir)
if err != nil {
panic(err)
}
authorizedUsersKeys := make(map[string][]ssh.PublicKey)
for _, file := range authorizedKeysFiles {
user := file.Name()
keys := []ssh.PublicKey{}
file, err := os.Open(fmt.Sprintf("%s/%s", authorizedKeysDir, user))
if err != nil {
log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() {
key, _, _, _, err := ssh.ParseAuthorizedKey(scanner.Bytes())
if err != nil {
panic(err)
}
keys = append(keys, key)
}
if err := scanner.Err(); err != nil {
log.Fatal(err)
}
authorizedUsersKeys[user] = keys
}
return func(ctx ssh.Context, key ssh.PublicKey) bool {
user := ctx.User()
log.Printf("user '%s' attempting to connect with authorized key", user)
keys, ok := authorizedUsersKeys[user]
if !ok {
keys = []ssh.PublicKey{}
}
authorized := false
for _, authKey := range keys {
if ssh.KeysEqual(key, authKey) {
authorized = true
break
}
}
log.Printf("user '%s' authorized: %t", user, authorized)
return authorized
}
}
func getPasswordHandler() ssh.PasswordHandler {
adminPassword := os.Getenv("ADMIN_PASSWORD")
if adminPassword == "" {
return nil
}
return func(ctx ssh.Context, password string) bool {
user := ctx.User()
log.Printf("user '%s' attempting to connect with password", user)
authorized := adminPassword == password
log.Printf("user '%s' authorized: %t", user, authorized)
return authorized
}
}