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