forgejo-federation/modules/ssh/ssh.go
zeripath 1d04e8641d
Set Setpgid on child git processes (#19865)
When Gitea is running as PID 1 git will occassionally orphan child processes leading
to (defunct) processes. This PR simply sets Setpgid to true on these child processes
meaning that these defunct processes will also be correctly reaped.

Fix #19077

Signed-off-by: Andrew Thornton <art27@cantab.net>
2022-06-03 15:36:18 +01:00

373 lines
10 KiB
Go

// Copyright 2017 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package ssh
import (
"bytes"
"context"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"fmt"
"io"
"net"
"os"
"os/exec"
"path/filepath"
"strconv"
"strings"
"sync"
"syscall"
asymkey_model "code.gitea.io/gitea/models/asymkey"
"code.gitea.io/gitea/modules/graceful"
"code.gitea.io/gitea/modules/log"
"code.gitea.io/gitea/modules/process"
"code.gitea.io/gitea/modules/setting"
"code.gitea.io/gitea/modules/util"
"github.com/gliderlabs/ssh"
gossh "golang.org/x/crypto/ssh"
)
type contextKey string
const giteaKeyID = contextKey("gitea-key-id")
func getExitStatusFromError(err error) int {
if err == nil {
return 0
}
exitErr, ok := err.(*exec.ExitError)
if !ok {
return 1
}
waitStatus, ok := exitErr.Sys().(syscall.WaitStatus)
if !ok {
// This is a fallback and should at least let us return something useful
// when running on Windows, even if it isn't completely accurate.
if exitErr.Success() {
return 0
}
return 1
}
return waitStatus.ExitStatus()
}
func sessionHandler(session ssh.Session) {
keyID := fmt.Sprintf("%d", session.Context().Value(giteaKeyID).(int64))
command := session.RawCommand()
log.Trace("SSH: Payload: %v", command)
args := []string{"serv", "key-" + keyID, "--config=" + setting.CustomConf}
log.Trace("SSH: Arguments: %v", args)
ctx, cancel := context.WithCancel(session.Context())
defer cancel()
cmd := exec.CommandContext(ctx, setting.AppPath, args...)
cmd.Env = append(
os.Environ(),
"SSH_ORIGINAL_COMMAND="+command,
"SKIP_MINWINSVC=1",
)
stdout, err := cmd.StdoutPipe()
if err != nil {
log.Error("SSH: StdoutPipe: %v", err)
return
}
defer stdout.Close()
stderr, err := cmd.StderrPipe()
if err != nil {
log.Error("SSH: StderrPipe: %v", err)
return
}
defer stderr.Close()
stdin, err := cmd.StdinPipe()
if err != nil {
log.Error("SSH: StdinPipe: %v", err)
return
}
defer stdin.Close()
process.SetSysProcAttribute(cmd)
wg := &sync.WaitGroup{}
wg.Add(2)
if err = cmd.Start(); err != nil {
log.Error("SSH: Start: %v", err)
return
}
go func() {
defer stdin.Close()
if _, err := io.Copy(stdin, session); err != nil {
log.Error("Failed to write session to stdin. %s", err)
}
}()
go func() {
defer wg.Done()
defer stdout.Close()
if _, err := io.Copy(session, stdout); err != nil {
log.Error("Failed to write stdout to session. %s", err)
}
}()
go func() {
defer wg.Done()
defer stderr.Close()
if _, err := io.Copy(session.Stderr(), stderr); err != nil {
log.Error("Failed to write stderr to session. %s", err)
}
}()
// Ensure all the output has been written before we wait on the command
// to exit.
wg.Wait()
// Wait for the command to exit and log any errors we get
err = cmd.Wait()
if err != nil {
log.Error("SSH: Wait: %v", err)
}
if err := session.Exit(getExitStatusFromError(err)); err != nil {
log.Error("Session failed to exit. %s", err)
}
}
func publicKeyHandler(ctx ssh.Context, key ssh.PublicKey) bool {
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Handle Public Key: Fingerprint: %s from %s", gossh.FingerprintSHA256(key), ctx.RemoteAddr())
}
if ctx.User() != setting.SSH.BuiltinServerUser {
log.Warn("Invalid SSH username %s - must use %s for all git operations via ssh", ctx.User(), setting.SSH.BuiltinServerUser)
log.Warn("Failed authentication attempt from %s", ctx.RemoteAddr())
return false
}
// check if we have a certificate
if cert, ok := key.(*gossh.Certificate); ok {
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Handle Certificate: %s Fingerprint: %s is a certificate", ctx.RemoteAddr(), gossh.FingerprintSHA256(key))
}
if len(setting.SSH.TrustedUserCAKeys) == 0 {
log.Warn("Certificate Rejected: No trusted certificate authorities for this server")
log.Warn("Failed authentication attempt from %s", ctx.RemoteAddr())
return false
}
// look for the exact principal
principalLoop:
for _, principal := range cert.ValidPrincipals {
pkey, err := asymkey_model.SearchPublicKeyByContentExact(ctx, principal)
if err != nil {
if asymkey_model.IsErrKeyNotExist(err) {
log.Debug("Principal Rejected: %s Unknown Principal: %s", ctx.RemoteAddr(), principal)
continue principalLoop
}
log.Error("SearchPublicKeyByContentExact: %v", err)
return false
}
c := &gossh.CertChecker{
IsUserAuthority: func(auth gossh.PublicKey) bool {
for _, k := range setting.SSH.TrustedUserCAKeysParsed {
if bytes.Equal(auth.Marshal(), k.Marshal()) {
return true
}
}
return false
},
}
// check the CA of the cert
if !c.IsUserAuthority(cert.SignatureKey) {
if log.IsDebug() {
log.Debug("Principal Rejected: %s Untrusted Authority Signature Fingerprint %s for Principal: %s", ctx.RemoteAddr(), gossh.FingerprintSHA256(cert.SignatureKey), principal)
}
continue principalLoop
}
// validate the cert for this principal
if err := c.CheckCert(principal, cert); err != nil {
// User is presenting an invalid certificate - STOP any further processing
if log.IsError() {
log.Error("Invalid Certificate KeyID %s with Signature Fingerprint %s presented for Principal: %s from %s", cert.KeyId, gossh.FingerprintSHA256(cert.SignatureKey), principal, ctx.RemoteAddr())
}
log.Warn("Failed authentication attempt from %s", ctx.RemoteAddr())
return false
}
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Successfully authenticated: %s Certificate Fingerprint: %s Principal: %s", ctx.RemoteAddr(), gossh.FingerprintSHA256(key), principal)
}
ctx.SetValue(giteaKeyID, pkey.ID)
return true
}
if log.IsWarn() {
log.Warn("From %s Fingerprint: %s is a certificate, but no valid principals found", ctx.RemoteAddr(), gossh.FingerprintSHA256(key))
log.Warn("Failed authentication attempt from %s", ctx.RemoteAddr())
}
return false
}
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Handle Public Key: %s Fingerprint: %s is not a certificate", ctx.RemoteAddr(), gossh.FingerprintSHA256(key))
}
pkey, err := asymkey_model.SearchPublicKeyByContent(ctx, strings.TrimSpace(string(gossh.MarshalAuthorizedKey(key))))
if err != nil {
if asymkey_model.IsErrKeyNotExist(err) {
if log.IsWarn() {
log.Warn("Unknown public key: %s from %s", gossh.FingerprintSHA256(key), ctx.RemoteAddr())
log.Warn("Failed authentication attempt from %s", ctx.RemoteAddr())
}
return false
}
log.Error("SearchPublicKeyByContent: %v", err)
return false
}
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Successfully authenticated: %s Public Key Fingerprint: %s", ctx.RemoteAddr(), gossh.FingerprintSHA256(key))
}
ctx.SetValue(giteaKeyID, pkey.ID)
return true
}
// sshConnectionFailed logs a failed connection
// - this mainly exists to give a nice function name in logging
func sshConnectionFailed(conn net.Conn, err error) {
// Log the underlying error with a specific message
log.Warn("Failed connection from %s with error: %v", conn.RemoteAddr(), err)
// Log with the standard failed authentication from message for simpler fail2ban configuration
log.Warn("Failed authentication attempt from %s", conn.RemoteAddr())
}
// Listen starts a SSH server listens on given port.
func Listen(host string, port int, ciphers, keyExchanges, macs []string) {
srv := ssh.Server{
Addr: net.JoinHostPort(host, strconv.Itoa(port)),
PublicKeyHandler: publicKeyHandler,
Handler: sessionHandler,
ServerConfigCallback: func(ctx ssh.Context) *gossh.ServerConfig {
config := &gossh.ServerConfig{}
config.KeyExchanges = keyExchanges
config.MACs = macs
config.Ciphers = ciphers
return config
},
ConnectionFailedCallback: sshConnectionFailed,
// We need to explicitly disable the PtyCallback so text displays
// properly.
PtyCallback: func(ctx ssh.Context, pty ssh.Pty) bool {
return false
},
}
keys := make([]string, 0, len(setting.SSH.ServerHostKeys))
for _, key := range setting.SSH.ServerHostKeys {
isExist, err := util.IsExist(key)
if err != nil {
log.Fatal("Unable to check if %s exists. Error: %v", setting.SSH.ServerHostKeys, err)
}
if isExist {
keys = append(keys, key)
}
}
if len(keys) == 0 {
filePath := filepath.Dir(setting.SSH.ServerHostKeys[0])
if err := os.MkdirAll(filePath, os.ModePerm); err != nil {
log.Error("Failed to create dir %s: %v", filePath, err)
}
err := GenKeyPair(setting.SSH.ServerHostKeys[0])
if err != nil {
log.Fatal("Failed to generate private key: %v", err)
}
log.Trace("New private key is generated: %s", setting.SSH.ServerHostKeys[0])
keys = append(keys, setting.SSH.ServerHostKeys[0])
}
for _, key := range keys {
log.Info("Adding SSH host key: %s", key)
err := srv.SetOption(ssh.HostKeyFile(key))
if err != nil {
log.Error("Failed to set Host Key. %s", err)
}
}
go func() {
_, _, finished := process.GetManager().AddTypedContext(graceful.GetManager().HammerContext(), "Service: Built-in SSH server", process.SystemProcessType, true)
defer finished()
listen(&srv)
}()
}
// GenKeyPair make a pair of public and private keys for SSH access.
// Public key is encoded in the format for inclusion in an OpenSSH authorized_keys file.
// Private Key generated is PEM encoded
func GenKeyPair(keyPath string) error {
privateKey, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
return err
}
privateKeyPEM := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)}
f, err := os.OpenFile(keyPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
return err
}
defer func() {
if err = f.Close(); err != nil {
log.Error("Close: %v", err)
}
}()
if err := pem.Encode(f, privateKeyPEM); err != nil {
return err
}
// generate public key
pub, err := gossh.NewPublicKey(&privateKey.PublicKey)
if err != nil {
return err
}
public := gossh.MarshalAuthorizedKey(pub)
p, err := os.OpenFile(keyPath+".pub", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
return err
}
defer func() {
if err = p.Close(); err != nil {
log.Error("Close: %v", err)
}
}()
_, err = p.Write(public)
return err
}