diff options
Diffstat (limited to 'modules/ssh/ssh.go')
| -rw-r--r-- | modules/ssh/ssh.go | 388 |
1 files changed, 388 insertions, 0 deletions
diff --git a/modules/ssh/ssh.go b/modules/ssh/ssh.go new file mode 100644 index 0000000..6ee10f7 --- /dev/null +++ b/modules/ssh/ssh.go @@ -0,0 +1,388 @@ +// Copyright 2017 The Gitea Authors. All rights reserved. +// SPDX-License-Identifier: MIT + +package ssh + +import ( + "bytes" + "context" + "crypto/rand" + "crypto/rsa" + "crypto/x509" + "encoding/pem" + "errors" + "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" +) + +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 := session.ConnPermissions().Extensions["forgejo-key-id"] + + command := session.RawCommand() + + log.Trace("SSH: Payload: %v", command) + + args := []string{"--config=" + setting.CustomConf, "serv", "key-" + keyID} + log.Trace("SSH: Arguments: %v", args) + + ctx, cancel := context.WithCancel(session.Context()) + defer cancel() + + gitProtocol := "" + for _, env := range session.Environ() { + if strings.HasPrefix(env, "GIT_PROTOCOL=") { + _, gitProtocol, _ = strings.Cut(env, "=") + break + } + } + + cmd := exec.CommandContext(ctx, setting.AppPath, args...) + cmd.Env = append( + os.Environ(), + "SSH_ORIGINAL_COMMAND="+command, + "SKIP_MINWINSVC=1", + "GIT_PROTOCOL="+gitProtocol, + ) + + 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 { + // Cannot use errors.Is here because ExitError doesn't implement Is + // Thus errors.Is will do equality test NOT type comparison + if _, ok := err.(*exec.ExitError); !ok { + log.Error("SSH: Wait: %v", err) + } + } + + if err := session.Exit(getExitStatusFromError(err)); err != nil && !errors.Is(err, io.EOF) { + 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 + } + + if cert.CertType != gossh.UserCert { + log.Warn("Certificate Rejected: Not a user certificate") + 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 { + marshaled := auth.Marshal() + for _, k := range setting.SSH.TrustedUserCAKeysParsed { + if bytes.Equal(marshaled, 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 + 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) + } + if ctx.Permissions().Extensions == nil { + ctx.Permissions().Extensions = map[string]string{} + } + ctx.Permissions().Extensions["forgejo-key-id"] = strconv.FormatInt(pkey.ID, 10) + + return true + } + + 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) { + 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)) + } + if ctx.Permissions().Extensions == nil { + ctx.Permissions().Extensions = map[string]string{} + } + ctx.Permissions().Extensions["forgejo-key-id"] = strconv.FormatInt(pkey.ID, 10) + + 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 +} |