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sftp: add support for ssh keys

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This commit is contained in:
Matthew Penner 2021-07-17 17:22:13 -06:00
parent 2a370a8776
commit d3360f0fd9
3 changed files with 209 additions and 29 deletions
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3
remote/types.go
View File

@ -70,6 +70,7 @@ type SftpAuthRequest struct {
IP string `json:"ip"`
SessionID []byte `json:"session_id"`
ClientVersion []byte `json:"client_version"`
Type string `json:"type"`
}
// SftpAuthResponse is returned by the Panel when a pair of SFTP credentials
@ -77,8 +78,8 @@ type SftpAuthRequest struct {
// matched as well as the permissions that are assigned to the authenticated
// user for the SFTP subsystem.
type SftpAuthResponse struct {
SSHKeys []string `json:"ssh_keys"`
Server string `json:"server"`
Token string `json:"token"`
Permissions []string `json:"permissions"`
}

2
sftp/handler.go
View File

@ -118,7 +118,7 @@ func (h *Handler) Filewrite(request *sftp.Request) (io.WriterAt, error) {
return f, nil
}
// Filecmd hander for basic SFTP system calls related to files, but not anything to do with reading
// Filecmd handler for basic SFTP system calls related to files, but not anything to do with reading
// or writing to those files.
func (h *Handler) Filecmd(request *sftp.Request) error {
if h.ro {

233
sftp/server.go
View File

@ -1,7 +1,11 @@
package sftp
import (
"bytes"
"context"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
@ -50,28 +54,21 @@ func New(m *server.Manager) *SFTPServer {
// Starts the SFTP server and add a persistent listener to handle inbound SFTP connections.
func (c *SFTPServer) Run() error {
if _, err := os.Stat(path.Join(c.BasePath, ".sftp/id_rsa")); os.IsNotExist(err) {
if err := c.generatePrivateKey(); err != nil {
return err
}
} else if err != nil {
return errors.Wrap(err, "sftp/server: could not stat private key file")
}
pb, err := ioutil.ReadFile(path.Join(c.BasePath, ".sftp/id_rsa"))
if err != nil {
return errors.Wrap(err, "sftp/server: could not read private key file")
}
private, err := ssh.ParsePrivateKey(pb)
keys, err := c.loadPrivateKeys()
if err != nil {
return err
}
conf := &ssh.ServerConfig{
NoClientAuth: false,
MaxAuthTries: 6,
PasswordCallback: c.passwordCallback,
NoClientAuth: false,
MaxAuthTries: 6,
PasswordCallback: c.passwordCallback,
PublicKeyCallback: c.publicKeyCallback,
}
for _, k := range keys {
conf.AddHostKey(k)
}
conf.AddHostKey(private)
listener, err := net.Listen("tcp", c.Listen)
if err != nil {
@ -104,7 +101,7 @@ func (c *SFTPServer) AcceptInbound(conn net.Conn, config *ssh.ServerConfig) {
// If its not a session channel we just move on because its not something we
// know how to handle at this point.
if ch.ChannelType() != "session" {
ch.Reject(ssh.UnknownChannelType, "unknown channel type")
_ = ch.Reject(ssh.UnknownChannelType, "unknown channel type")
continue
}
@ -118,7 +115,7 @@ func (c *SFTPServer) AcceptInbound(conn net.Conn, config *ssh.ServerConfig) {
// Channels have a type that is dependent on the protocol. For SFTP
// this is "subsystem" with a payload that (should) be "sftp". Discard
// anything else we receive ("pty", "shell", etc)
req.Reply(req.Type == "subsystem" && string(req.Payload[4:]) == "sftp", nil)
_ = req.Reply(req.Type == "subsystem" && string(req.Payload[4:]) == "sftp", nil)
}
}(requests)
@ -136,6 +133,7 @@ func (c *SFTPServer) AcceptInbound(conn net.Conn, config *ssh.ServerConfig) {
return s.ID() == uuid
})
if srv == nil {
_ = conn.Close()
continue
}
@ -143,31 +141,153 @@ func (c *SFTPServer) AcceptInbound(conn net.Conn, config *ssh.ServerConfig) {
// them access to the underlying filesystem.
handler := sftp.NewRequestServer(channel, NewHandler(sconn, srv.Filesystem()).Handlers())
if err := handler.Serve(); err == io.EOF {
handler.Close()
_ = handler.Close()
}
}
}
// Generates a private key that will be used by the SFTP server.
func (c *SFTPServer) generatePrivateKey() error {
key, err := rsa.GenerateKey(rand.Reader, 2048)
func (c *SFTPServer) loadPrivateKeys() ([]ssh.Signer, error) {
if _, err := os.Stat(path.Join(c.BasePath, ".sftp/id_rsa")); err != nil {
if !os.IsNotExist(err) {
return nil, err
}
if err := c.generateRSAPrivateKey(); err != nil {
return nil, err
}
}
rsaBytes, err := ioutil.ReadFile(path.Join(c.BasePath, ".sftp/id_rsa"))
if err != nil {
return errors.WithStack(err)
return nil, errors.Wrap(err, "sftp/server: could not read private key file")
}
rsaPrivateKey, err := ssh.ParsePrivateKey(rsaBytes)
if err != nil {
return nil, err
}
if _, err := os.Stat(path.Join(c.BasePath, ".sftp/id_ecdsa")); err != nil {
if !os.IsNotExist(err) {
return nil, err
}
if err := c.generateECDSAPrivateKey(); err != nil {
return nil, err
}
}
ecdsaBytes, err := ioutil.ReadFile(path.Join(c.BasePath, ".sftp/id_ecdsa"))
if err != nil {
return nil, errors.Wrap(err, "sftp/server: could not read private key file")
}
ecdsaPrivateKey, err := ssh.ParsePrivateKey(ecdsaBytes)
if err != nil {
return nil, err
}
if _, err := os.Stat(path.Join(c.BasePath, ".sftp/id_ed25519")); err != nil {
if !os.IsNotExist(err) {
return nil, err
}
if err := c.generateEd25519PrivateKey(); err != nil {
return nil, err
}
}
ed25519Bytes, err := ioutil.ReadFile(path.Join(c.BasePath, ".sftp/id_ed25519"))
if err != nil {
return nil, errors.Wrap(err, "sftp/server: could not read private key file")
}
ed25519PrivateKey, err := ssh.ParsePrivateKey(ed25519Bytes)
if err != nil {
return nil, err
}
return []ssh.Signer{
rsaPrivateKey,
ecdsaPrivateKey,
ed25519PrivateKey,
}, nil
}
// generateRSAPrivateKey generates a RSA-4096 private key that will be used by the SFTP server.
func (c *SFTPServer) generateRSAPrivateKey() error {
key, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
return err
}
if err := os.MkdirAll(path.Join(c.BasePath, ".sftp"), 0755); err != nil {
return errors.Wrap(err, "sftp/server: could not create .sftp directory")
}
o, err := os.OpenFile(path.Join(c.BasePath, ".sftp/id_rsa"), os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return errors.WithStack(err)
return err
}
defer o.Close()
err = pem.Encode(o, &pem.Block{
if err := pem.Encode(o, &pem.Block{
Type: "RSA PRIVATE KEY",
Bytes: x509.MarshalPKCS1PrivateKey(key),
})
return errors.WithStack(err)
}); err != nil {
return err
}
return nil
}
// generateECDSAPrivateKey generates a ECDSA-P256 private key that will be used by the SFTP server.
func (c *SFTPServer) generateECDSAPrivateKey() error {
key, err := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
if err != nil {
return err
}
if err := os.MkdirAll(path.Join(c.BasePath, ".sftp"), 0755); err != nil {
return errors.Wrap(err, "sftp/server: could not create .sftp directory")
}
o, err := os.OpenFile(path.Join(c.BasePath, ".sftp/id_ecdsa"), os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return err
}
defer o.Close()
privBytes, err := x509.MarshalPKCS8PrivateKey(key)
if err != nil {
return err
}
if err := pem.Encode(o, &pem.Block{
Type: "PRIVATE KEY",
Bytes: privBytes,
}); err != nil {
return err
}
return nil
}
// generateEd25519PrivateKey generates a ed25519 private key that will be used by the SFTP server.
func (c *SFTPServer) generateEd25519PrivateKey() error {
_, key, err := ed25519.GenerateKey(rand.Reader)
if err != nil {
return err
}
if err := os.MkdirAll(path.Join(c.BasePath, ".sftp"), 0755); err != nil {
return errors.Wrap(err, "sftp/server: could not create .sftp directory")
}
o, err := os.OpenFile(path.Join(c.BasePath, ".sftp/id_ed25519"), os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return err
}
defer o.Close()
privBytes, err := x509.MarshalPKCS8PrivateKey(key)
if err != nil {
return err
}
if err := pem.Encode(o, &pem.Block{
Type: "PRIVATE KEY",
Bytes: privBytes,
}); err != nil {
return err
}
return nil
}
// A function capable of validating user credentials with the Panel API.
@ -178,6 +298,7 @@ func (c *SFTPServer) passwordCallback(conn ssh.ConnMetadata, pass []byte) (*ssh.
IP: conn.RemoteAddr().String(),
SessionID: conn.SessionID(),
ClientVersion: conn.ClientVersion(),
Type: "password",
}
logger := log.WithFields(log.Fields{"subsystem": "sftp", "username": conn.User(), "ip": conn.RemoteAddr().String()})
@ -188,6 +309,11 @@ func (c *SFTPServer) passwordCallback(conn ssh.ConnMetadata, pass []byte) (*ssh.
return nil, &remote.SftpInvalidCredentialsError{}
}
if len(pass) < 1 {
logger.Warn("failed to validate user credentials (invalid format)")
return nil, &remote.SftpInvalidCredentialsError{}
}
resp, err := c.manager.Client().ValidateSftpCredentials(context.Background(), request)
if err != nil {
if _, ok := err.(*remote.SftpInvalidCredentialsError); ok {
@ -209,3 +335,56 @@ func (c *SFTPServer) passwordCallback(conn ssh.ConnMetadata, pass []byte) (*ssh.
return sshPerm, nil
}
func (c *SFTPServer) publicKeyCallback(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
request := remote.SftpAuthRequest{
User: conn.User(),
Pass: "KEKW",
IP: conn.RemoteAddr().String(),
SessionID: conn.SessionID(),
ClientVersion: conn.ClientVersion(),
Type: "publicKey",
}
logger := log.WithFields(log.Fields{"subsystem": "sftp", "username": conn.User(), "ip": conn.RemoteAddr().String()})
logger.Debug("validating public key for SFTP connection")
if !validUsernameRegexp.MatchString(request.User) {
logger.Warn("failed to validate user credentials (invalid format)")
return nil, &remote.SftpInvalidCredentialsError{}
}
resp, err := c.manager.Client().ValidateSftpCredentials(context.Background(), request)
if err != nil {
if _, ok := err.(*remote.SftpInvalidCredentialsError); ok {
logger.Warn("failed to validate user credentials (invalid username or password)")
} else {
logger.WithField("error", err).Error("encountered an error while trying to validate user credentials")
}
return nil, err
}
if len(resp.SSHKeys) < 1 {
return nil, &remote.SftpInvalidCredentialsError{}
}
for _, k := range resp.SSHKeys {
storedPublicKey, _, _, _, err := ssh.ParseAuthorizedKey([]byte(k))
if err != nil {
return nil, err
}
if !bytes.Equal(key.Marshal(), storedPublicKey.Marshal()) {
continue
}
return &ssh.Permissions{
Extensions: map[string]string{
"uuid": resp.Server,
"user": conn.User(),
"permissions": strings.Join(resp.Permissions, ","),
},
}, nil
}
return nil, &remote.SftpInvalidCredentialsError{}
}