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ssh.go
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ssh.go
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package main
import (
"crypto/x509"
"encoding/pem"
"errors"
"fmt"
"golang.org/x/crypto/ssh/agent"
"io"
"net"
"os"
"strings"
"go.uber.org/zap"
"golang.org/x/crypto/ssh"
)
func startSshTunnel(c *Config) {
if c.Tunnel == "" {
return
}
tunnelSplit := strings.Split(c.Tunnel, "@")
username, tunnel := tunnelSplit[0], tunnelSplit[1]
tunnelSplit = strings.Split(tunnel, ":")
tunnel, publishPort := strings.Join(tunnelSplit[:len(tunnelSplit)-1], ":"), tunnelSplit[len(tunnelSplit)-1]
sshConfig := &ssh.ClientConfig{
User: username,
Auth: []ssh.AuthMethod{},
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
}
if c.PrivateKeyPath != "" {
if auth, err := withKey(c.PrivateKeyPath, c.PrivateKeyPass); err == nil {
sshConfig.Auth = append(sshConfig.Auth, auth)
} else {
logs.FatalIf(err, "loading private key failed")
}
} else if os.Getenv("SSH_AUTH_SOCK") != "" {
// ssh-agent(1) provides a UNIX socket at $SSH_AUTH_SOCK.
agentConnection, err := net.Dial("unix", os.Getenv("SSH_AUTH_SOCK"))
logs.FatalIf(err, "opening SSH_AUTH_SOCK")
sshConfig.Auth = append(sshConfig.Auth, ssh.PublicKeysCallback(agent.NewClient(agentConnection).Signers))
}
sshClient, err := ssh.Dial("tcp", tunnel, sshConfig)
logs.FatalIf(err, "dialing ssh server")
defer func() { _ = sshClient.Close() }()
// Listen on remote server port
listener, err := sshClient.Listen("tcp", fmt.Sprintf("0.0.0.0:%s", publishPort))
logs.FatalIf(err, "opening port on remote server")
defer func() { _ = listener.Close() }()
logs.Info("listening on remote server", zap.String("host", listener.Addr().String()))
for {
remote, err := listener.Accept()
logs.FatalIf(err, "error accepting connection")
local, err := net.Dial("tcp", c.ListenAddress)
logs.FatalIf(err, "dialing local service")
err = handleClient(local, remote)
logs.ErrorIf(err, "handling transport")
_ = remote.Close()
_ = local.Close()
}
}
func withKey(privateKeyPath, privateKeyPassword string) (ssh.AuthMethod, error) {
// read private key file
pemBytes, err := os.ReadFile(privateKeyPath)
if err != nil {
return nil, fmt.Errorf("Reading private key file failed %v", err)
}
// create signer
signer, err := signerFromPem(pemBytes, []byte(privateKeyPassword))
if err != nil {
return nil, err
}
return ssh.PublicKeys(signer), nil
}
// From https://sosedoff.com/2015/05/25/ssh-port-forwarding-with-go.html
// Handle local client connections and tunnel data to the remote server
// Will use io.Copy - http://golang.org/pkg/io/#Copy
func handleClient(local net.Conn, remote net.Conn) error {
chDone := make(chan error)
// Start remote -> local data transfer
go func() {
_, err := io.Copy(local, remote)
logs.ErrorIf(err, "error while copy remote->local")
chDone <- err
}()
// Start local -> remote data transfer
go func() {
_, err := io.Copy(remote, local)
logs.ErrorIf(err, "error while copy local->remote")
chDone <- err
}()
return <-chDone
}
func signerFromPem(pemBytes []byte, password []byte) (ssh.Signer, error) {
// read pem block
err := errors.New("Pem decode failed, no key found")
pemBlock, _ := pem.Decode(pemBytes)
if pemBlock == nil {
return nil, err
}
// handle encrypted key
if x509.IsEncryptedPEMBlock(pemBlock) {
// decrypt PEM
pemBlock.Bytes, err = x509.DecryptPEMBlock(pemBlock, []byte(password))
if err != nil {
return nil, fmt.Errorf("Decrypting PEM block failed %v", err)
}
// get RSA, EC or DSA key
key, err := parsePemBlock(pemBlock)
if err != nil {
return nil, err
}
// generate signer instance from key
signer, err := ssh.NewSignerFromKey(key)
if err != nil {
return nil, fmt.Errorf("Creating signer from encrypted key failed %v", err)
}
return signer, nil
} else {
// generate signer instance from plain key
signer, err := ssh.ParsePrivateKey(pemBytes)
if err != nil {
return nil, fmt.Errorf("Parsing plain private key failed %v", err)
}
return signer, nil
}
}
func parsePemBlock(block *pem.Block) (interface{}, error) {
switch block.Type {
case "RSA PRIVATE KEY":
key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("Parsing PKCS private key failed %v", err)
} else {
return key, nil
}
case "EC PRIVATE KEY":
key, err := x509.ParseECPrivateKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("Parsing EC private key failed %v", err)
} else {
return key, nil
}
case "DSA PRIVATE KEY":
key, err := ssh.ParseDSAPrivateKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("Parsing DSA private key failed %v", err)
} else {
return key, nil
}
default:
return nil, fmt.Errorf("Parsing private key failed, unsupported key type %q", block.Type)
}
}