internal/sshd/sshd.go
581 lines · 17590 bytes
1// Package sshd implements the embedded SSH listener: public-key auth against
2// registered keys, then dispatch to git transport or control commands.
3package sshd
4
5import (
6 "context"
7 "crypto/ed25519"
8 "crypto/rand"
9 "encoding/base64"
10 "encoding/pem"
11 "errors"
12 "fmt"
13 "io"
14 "log/slog"
15 "maps"
16 "net"
17 "os"
18 "path/filepath"
19 "slices"
20 "strconv"
21 "sync"
22 "sync/atomic"
23 "time"
24
25 "golang.org/x/crypto/ssh"
26
27 "gitbay.org/gitbay/internal/config"
28 "gitbay.org/gitbay/internal/control"
29 "gitbay.org/gitbay/internal/gitutil"
30 "gitbay.org/gitbay/internal/hookd"
31 "gitbay.org/gitbay/internal/policy"
32 "gitbay.org/gitbay/internal/protocol"
33 "gitbay.org/gitbay/internal/store"
34)
35
36type Server struct {
37 cfg config.Config
38 st *store.Store
39 sshCfg *ssh.ServerConfig
40 authLimiter *rateLimiter
41 sessions sync.WaitGroup // accepted connections still being served
42 mu sync.Mutex
43 conns map[*conn]struct{}
44 stopping chan struct{} // closed by Stop
45 stopOnce sync.Once
46}
47
48// conn is one accepted connection and how many sessions it is running.
49// A CLI's shared connection sits idle between commands; on shutdown an
50// idle connection is closed at once and only a session mid-command is
51// waited for (#141).
52type conn struct {
53 net net.Conn
54 active atomic.Int32
55 // keyID and userID are the key that authenticated the connection and
56 // its account: 0 before the handshake and for an unregistered key.
57 // Guarded by Server.mu.
58 keyID, userID int64
59 revoked chan struct{} // closed by cut
60 cutOnce sync.Once
61}
62
63// cut ends the connection because its key was revoked: a git transport
64// on it is killed, and every other command loses its channel.
65func (c *conn) cut() {
66 c.cutOnce.Do(func() { close(c.revoked) })
67 c.net.Close()
68}
69
70func New(cfg config.Config, st *store.Store) (*Server, error) {
71 s := &Server{cfg: cfg, st: st, authLimiter: newRateLimiter(cfg.Limits.SSHAuthRate, time.Minute), conns: map[*conn]struct{}{}, stopping: make(chan struct{})}
72
73 sc := &ssh.ServerConfig{
74 PublicKeyCallback: s.authenticate,
75 ServerVersion: "SSH-2.0-gitbayd",
76 }
77 signers, err := loadHostKeys(cfg)
78 if err != nil {
79 return nil, err
80 }
81 for _, sg := range signers {
82 sc.AddHostKey(sg)
83 }
84 s.sshCfg = sc
85 st.OnRevoke(s.revoke)
86 return s, nil
87}
88
89// loadHostKeys loads the configured host keys, or generates an ed25519 key
90// under server.root/ssh/ when none are configured.
91func loadHostKeys(cfg config.Config) ([]ssh.Signer, error) {
92 paths := cfg.SSH.HostKeys
93 if len(paths) == 0 {
94 p := filepath.Join(cfg.Server.Root, "ssh", "host_ed25519")
95 if _, err := os.Stat(p); errors.Is(err, os.ErrNotExist) {
96 if err := generateHostKey(p); err != nil {
97 return nil, fmt.Errorf("generating host key: %w", err)
98 }
99 slog.Info("generated ssh host key", "path", p)
100 }
101 paths = []string{p}
102 }
103 var signers []ssh.Signer
104 for _, p := range paths {
105 raw, err := os.ReadFile(p)
106 if err != nil {
107 return nil, fmt.Errorf("host key %s: %w", p, err)
108 }
109 sg, err := ssh.ParsePrivateKey(raw)
110 if err != nil {
111 return nil, fmt.Errorf("host key %s: %w", p, err)
112 }
113 signers = append(signers, sg)
114 }
115 return signers, nil
116}
117
118func generateHostKey(path string) error {
119 if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
120 return err
121 }
122 _, priv, err := ed25519.GenerateKey(rand.Reader)
123 if err != nil {
124 return err
125 }
126 block, err := ssh.MarshalPrivateKey(priv, "")
127 if err != nil {
128 return err
129 }
130 return os.WriteFile(path, pem.EncodeToMemory(block), 0o600)
131}
132
133// authenticate resolves the presented key to a registered account. The SSH
134// username is ignored; identity comes from the key alone. When registration
135// is open or invite-based, unknown keys are admitted to run exactly one
136// command: register.
137func (s *Server) authenticate(meta ssh.ConnMetadata, pub ssh.PublicKey) (*ssh.Permissions, error) {
138 ip := remoteIP(meta.RemoteAddr())
139 if !s.authLimiter.allow(ip) {
140 // One audit entry per throttled window, not per rejected attempt.
141 if s.authLimiter.firstThrottle(ip) {
142 s.st.Audit(0, "auth.throttled", map[string]any{"ip": ip, "rate": s.cfg.Limits.SSHAuthRate})
143 }
144 return nil, fmt.Errorf("too many authentication attempts; try again shortly")
145 }
146 fp := ssh.FingerprintSHA256(pub)
147 key, err := s.st.SSHKeyByFingerprint(fp)
148 if err != nil && !errors.Is(err, store.ErrNotFound) {
149 // The store, not the key, failed. Neither a failure against the
150 // limiter nor "unknown key": a busy database during a restart
151 // would otherwise lock every client out for a minute.
152 slog.Error("ssh auth: key lookup", "err", err)
153 return nil, fmt.Errorf("authentication temporarily unavailable")
154 }
155 if err != nil {
156 if s.cfg.Registration.Mode != "closed" {
157 return &ssh.Permissions{Extensions: map[string]string{
158 "anon-key": base64.StdEncoding.EncodeToString(pub.Marshal()),
159 }}, nil
160 }
161 s.authLimiter.fail(ip)
162 s.st.Audit(0, "auth.failed", map[string]any{"ip": ip, "fingerprint": fp})
163 return nil, fmt.Errorf("unknown key %s", fp)
164 }
165 if key.Expired(time.Now()) {
166 s.st.Audit(key.UserID, "auth.expired", map[string]any{"ip": ip, "fingerprint": fp})
167 return nil, fmt.Errorf("key %s has expired", fp)
168 }
169 s.authLimiter.success(ip)
170 return &ssh.Permissions{Extensions: map[string]string{
171 "user-id": strconv.FormatInt(key.UserID, 10),
172 "key-id": strconv.FormatInt(key.ID, 10),
173 }}, nil
174}
175
176// Serve accepts connections on ln until it is closed.
177func (s *Server) Serve(ln net.Listener) error {
178 served := make(chan struct{})
179 defer close(served)
180 go s.sweep(served)
181 for {
182 nc, err := ln.Accept()
183 if err != nil {
184 return err
185 }
186 c := &conn{net: nc, revoked: make(chan struct{})}
187 s.mu.Lock()
188 s.conns[c] = struct{}{}
189 s.mu.Unlock()
190 s.sessions.Add(1)
191 go func() {
192 defer s.sessions.Done()
193 defer func() {
194 s.mu.Lock()
195 delete(s.conns, c)
196 s.mu.Unlock()
197 }()
198 s.handleConn(c)
199 }()
200 }
201}
202
203// revoke closes the connections opened by the keys r names.
204func (s *Server) revoke(r store.Revoked) {
205 var cut []*conn
206 s.mu.Lock()
207 for c := range s.conns {
208 if c.keyID == 0 {
209 continue
210 }
211 if (r.UserID != 0 && c.userID == r.UserID) || slices.Contains(r.KeyIDs, c.keyID) {
212 cut = append(cut, c)
213 }
214 }
215 s.mu.Unlock()
216 for _, c := range cut {
217 c.cut()
218 }
219}
220
221// sweepInterval bounds how long a revocation this process was not told
222// about (gitbayd admin on the host) leaves a connection open.
223const sweepInterval = 15 * time.Second
224
225func (s *Server) sweep(served <-chan struct{}) {
226 t := time.NewTicker(sweepInterval)
227 defer t.Stop()
228 for {
229 select {
230 case <-t.C:
231 s.sweepOnce()
232 case <-served:
233 return
234 case <-s.stopping:
235 return
236 }
237 }
238}
239
240// sweepOnce cuts every connection whose key is no longer live. Only
241// connections whose key was asked about are judged: one that
242// authenticated while the query ran waits for the next sweep.
243func (s *Server) sweepOnce() {
244 asked := map[int64]bool{}
245 s.mu.Lock()
246 for c := range s.conns {
247 if c.keyID != 0 {
248 asked[c.keyID] = true
249 }
250 }
251 s.mu.Unlock()
252 if len(asked) == 0 {
253 return
254 }
255 live, err := s.st.LiveSSHKeys(slices.Collect(maps.Keys(asked)))
256 if err != nil {
257 slog.Error("ssh sweep: key lookup", "err", err)
258 return
259 }
260 var cut []*conn
261 s.mu.Lock()
262 for c := range s.conns {
263 if asked[c.keyID] && !live[c.keyID] {
264 cut = append(cut, c)
265 }
266 }
267 s.mu.Unlock()
268 for _, c := range cut {
269 c.cut()
270 }
271}
272
273// Stop ends the commands that run until something happens (build log
274// --follow), so a shutdown drain waits only for work that finishes. It
275// does not close connections; Shutdown does.
276func (s *Server) Stop() {
277 s.stopOnce.Do(func() { close(s.stopping) })
278}
279
280// Shutdown closes every idle connection, then waits for the ones with a
281// session running, or for ctx. The caller closes the listener first; a
282// push in flight completes rather than being cut mid-pack.
283func (s *Server) Shutdown(ctx context.Context) error {
284 s.Stop()
285 s.mu.Lock()
286 for c := range s.conns {
287 if c.active.Load() == 0 {
288 c.net.Close()
289 }
290 }
291 s.mu.Unlock()
292 done := make(chan struct{})
293 go func() {
294 s.sessions.Wait()
295 close(done)
296 }()
297 select {
298 case <-done:
299 return nil
300 case <-ctx.Done():
301 return ctx.Err()
302 }
303}
304
305func (s *Server) handleConn(c *conn) {
306 defer c.net.Close()
307 sconn, chans, reqs, err := ssh.NewServerConn(c.net, s.sshCfg)
308 if err != nil {
309 return
310 }
311 defer sconn.Close()
312 ext := sconn.Permissions.Extensions
313 s.mu.Lock()
314 c.keyID, _ = strconv.ParseInt(ext["key-id"], 10, 64)
315 c.userID, _ = strconv.ParseInt(ext["user-id"], 10, 64)
316 s.mu.Unlock()
317 go ssh.DiscardRequests(reqs)
318
319 for newCh := range chans {
320 if newCh.ChannelType() != "session" {
321 newCh.Reject(ssh.UnknownChannelType, "only session channels are supported")
322 continue
323 }
324 ch, chReqs, err := newCh.Accept()
325 if err != nil {
326 continue
327 }
328 c.active.Add(1)
329 go func() {
330 defer c.active.Add(-1)
331 s.handleSession(c, sconn, ch, chReqs)
332 }()
333 }
334}
335
336func (s *Server) handleSession(c *conn, sconn *ssh.ServerConn, ch ssh.Channel, reqs <-chan *ssh.Request) {
337 defer ch.Close()
338 var term control.Term
339 for req := range reqs {
340 switch req.Type {
341 case "exec":
342 var payload struct{ Command string }
343 if err := ssh.Unmarshal(req.Payload, &payload); err != nil {
344 req.Reply(false, nil)
345 continue
346 }
347 req.Reply(true, nil)
348 // x/crypto closes reqs when the client closes the channel. That
349 // is how a follow learns nobody is reading: the CLI's shared
350 // connection outlives a Ctrl-C, the channel does not. Stop
351 // ends it too, for a restart.
352 closed := make(chan struct{})
353 go func() {
354 for r := range reqs {
355 r.Reply(false, nil)
356 }
357 close(closed)
358 }()
359 done := make(chan struct{})
360 go func() {
361 select {
362 case <-closed:
363 case <-s.stopping:
364 }
365 close(done)
366 }()
367 code := s.runExec(c, sconn, ch, term, payload.Command, done)
368 sendExit(ch, code)
369 return
370 case "shell":
371 req.Reply(true, nil)
372 fmt.Fprintf(ch, "gitbay control plane: interactive shells are not available.\nTry: ssh %s help\n", s.cfg.Server.SiteURL)
373 sendExit(ch, protocol.ExitUsage)
374 return
375 case "env":
376 var kv struct{ Name, Value string }
377 if ssh.Unmarshal(req.Payload, &kv) == nil && kv.Name == "GITBAY_TERM" {
378 term = control.ParseTerm(kv.Value)
379 }
380 req.Reply(true, nil)
381 case "pty-req":
382 // Harmless; accept and ignore.
383 req.Reply(true, nil)
384 default:
385 req.Reply(false, nil)
386 }
387 }
388}
389
390func sendExit(ch ssh.Channel, code int) {
391 var msg = struct{ Status uint32 }{uint32(code)}
392 ch.SendRequest("exit-status", false, ssh.Marshal(&msg))
393}
394
395func (s *Server) runExec(c *conn, sconn *ssh.ServerConn, ch ssh.Channel, term control.Term, cmdline string, done <-chan struct{}) int {
396 ext := sconn.Permissions.Extensions
397 if blob := ext["anon-key"]; blob != "" {
398 return s.runAnonymous(ch, blob, cmdline)
399 }
400 userID, _ := strconv.ParseInt(ext["user-id"], 10, 64)
401 keyID, _ := strconv.ParseInt(ext["key-id"], 10, 64)
402 // A connection outlives its commands, so the key is read again for
403 // each one: what it may do is what it may do now (#256).
404 key, err := s.st.SSHKeyByID(keyID)
405 if errors.Is(err, store.ErrNotFound) || (err == nil && key.UserID != userID) {
406 fmt.Fprintln(ch.Stderr(), "this key is no longer registered")
407 return protocol.ExitDenied
408 }
409 if err != nil {
410 slog.Error("ssh exec: key lookup", "err", err)
411 fmt.Fprintln(ch.Stderr(), "authentication temporarily unavailable")
412 return protocol.ExitFailure
413 }
414 if key.Expired(time.Now()) {
415 fmt.Fprintln(ch.Stderr(), "this key has expired; remove it and add a new one")
416 return protocol.ExitDenied
417 }
418 user, err := s.st.UserByID(userID)
419 if err != nil {
420 fmt.Fprintln(ch.Stderr(), "account no longer exists")
421 return protocol.ExitDenied
422 }
423 _ = s.st.TouchSSHKey(keyID)
424 return Exec(s.cfg, s.st, user, key, term, cmdline, ch, ch, ch.Stderr(), done, s.stopping, c.revoked)
425}
426
427// runAnonymous handles a session from an unregistered key: the register
428// command and nothing else.
429func (s *Server) runAnonymous(ch ssh.Channel, keyB64, cmdline string) int {
430 raw, err := base64.StdEncoding.DecodeString(keyB64)
431 if err != nil {
432 return protocol.ExitFailure
433 }
434 pub, err := ssh.ParsePublicKey(raw)
435 if err != nil {
436 return protocol.ExitFailure
437 }
438 argv, err := protocol.Tokenize(cmdline)
439 if err != nil {
440 fmt.Fprintf(ch.Stderr(), "cannot parse command: %v\n", err)
441 return protocol.ExitUsage
442 }
443 if len(argv) == 0 || argv[0] != "register" {
444 fmt.Fprintf(ch.Stderr(), "this key is not registered here. Create an account with:\n ssh <host> register --username <name> %s\n",
445 map[string]string{"open": "--email <address>", "invite": "--invite <code>"}[s.cfg.Registration.Mode])
446 return protocol.ExitDenied
447 }
448 return control.RunRegister(s.cfg, s.st, pub, argv, ch, ch.Stderr())
449}
450
451// Exec runs one SSH exec command line for an authenticated key. It is the
452// single dispatch path shared by the embedded listener and the system-sshd
453// forced command (gitbayd shell). Closing revoked kills a git transport.
454func Exec(cfg config.Config, st *store.Store, user store.User, key store.SSHKey, term control.Term, cmdline string,
455 stdin io.Reader, stdout, stderr io.Writer, done, stopping, revoked <-chan struct{}) int {
456 if user.Disabled {
457 fmt.Fprintln(stderr, "this account is disabled; contact the instance admin")
458 return protocol.ExitDenied
459 }
460 argv, err := protocol.Tokenize(cmdline)
461 if err != nil {
462 fmt.Fprintf(stderr, "cannot parse command: %v\n", err)
463 return protocol.ExitUsage
464 }
465 if len(argv) > 0 {
466 switch argv[0] {
467 case "git-upload-pack", "git-receive-pack", "git-upload-archive":
468 if user.Pending {
469 fmt.Fprintln(stderr, "your account is not active yet: verify your email first")
470 return protocol.ExitDenied
471 }
472 return runGit(cfg, st, user, key.Scope, argv, stdin, stdout, stderr, revoked)
473 case "git-lfs-authenticate":
474 // Part of the git transport, not the control plane: usable by
475 // git-scoped and deploy keys, with the transports' access rules.
476 if user.Pending {
477 fmt.Fprintln(stderr, "your account is not active yet: verify your email first")
478 return protocol.ExitDenied
479 }
480 return runLFSAuthenticate(cfg, st, user, key.Scope, argv, stdout, stderr)
481 }
482 }
483 ctx := &control.Ctx{
484 User: user,
485 Scope: key.Scope,
486 Source: key.Fingerprint,
487 Term: term,
488 Store: st,
489 Cfg: cfg,
490 Stdin: stdin,
491 Stdout: stdout,
492 Stderr: stderr,
493 Done: done,
494 Stopping: stopping,
495 Expires: key.ExpiresAt,
496 }
497 return control.Dispatch(ctx, argv)
498}
499
500// runGit streams a git transport service after access checks.
501func runGit(cfg config.Config, st *store.Store, user store.User, scope string, argv []string,
502 stdin io.Reader, stdout, stderr io.Writer, revoked <-chan struct{}) int {
503 service := argv[0]
504 if len(argv) != 2 {
505 fmt.Fprintf(stderr, "usage: %s <path>\n", service)
506 return protocol.ExitUsage
507 }
508 write := service == "git-receive-pack"
509
510 repo, err := st.RepoByPath(argv[1])
511 if err != nil {
512 fmt.Fprintln(stderr, "repository not found")
513 return protocol.ExitNotFound
514 }
515 if policy.IsDeployScope(scope) {
516 // A deploy key authorizes by its binding alone: one repository,
517 // its mode, nothing inherited from whoever registered it. Any
518 // mismatch reads as nonexistence, same as the access rules.
519 if !policy.DeployScopeAllows(scope, repo.ID, write) {
520 fmt.Fprintln(stderr, "repository not found")
521 return protocol.ExitNotFound
522 }
523 } else {
524 grant, err := st.AccessRole(repo.ID, user.ID)
525 if err != nil {
526 fmt.Fprintln(stderr, "internal error")
527 return protocol.ExitFailure
528 }
529 if !policy.CanRead(user, repo, grant) {
530 // Same answer as nonexistence: private repos must not be enumerable.
531 fmt.Fprintln(stderr, "repository not found")
532 return protocol.ExitNotFound
533 }
534 if !policy.ScopeAllowsGit(scope, repo.Path(), write) {
535 fmt.Fprintf(stderr, "this key's scope (%s) does not allow %s on %s\n", scope, service, repo.Path())
536 return protocol.ExitDenied
537 }
538 if write && !policy.CanWrite(user, repo, grant) {
539 fmt.Fprintf(stderr, "write access to %s denied\n", repo.Path())
540 return protocol.ExitDenied
541 }
542 }
543 if write && repo.Settings.Archived {
544 fmt.Fprintf(stderr, "%s is archived and read-only\n", repo.Path())
545 return protocol.ExitDenied
546 }
547 if write {
548 if mirrored, err := st.PullMirrored(repo.ID); err == nil && mirrored {
549 fmt.Fprintf(stderr, "%s is a pull mirror: its refs come from the upstream; push there instead\n", repo.Path())
550 return protocol.ExitDenied
551 }
552 }
553
554 dir := control.RepoDir(cfg.Server.Root, repo.OwnerName, repo.Name)
555 env := []string{
556 hookd.EnvSocket + "=" + hookd.SocketPath(cfg.Server.Root),
557 hookd.EnvRepoID + "=" + strconv.FormatInt(repo.ID, 10),
558 hookd.EnvUserID + "=" + strconv.FormatInt(user.ID, 10),
559 hookd.EnvScope + "=" + scope,
560 }
561 // A storage quota on the owner rides the same mechanism as the pack
562 // cap: the pack may be no larger than what the owner has left.
563 maxPack := cfg.Limits.MaxPackBytes
564 if write && repo.OwnerKind == "user" {
565 if limit := control.ByteLimit(st, control.QuotaConfig(cfg), repo.OwnerID); limit > 0 {
566 used := control.OwnedBytes(st, cfg.Server.Root, repo.OwnerID)
567 left := limit - used
568 if left <= 0 {
569 fmt.Fprintf(stderr, "%s's storage quota is used up (%d of %d bytes); delete something, or ask an admin to raise the limit\n", repo.OwnerName, used, limit)
570 return protocol.ExitDenied
571 }
572 if maxPack == 0 || left < maxPack {
573 maxPack = left
574 }
575 }
576 }
577 if err := gitutil.Transport(service, dir, stdin, stdout, stderr, env, maxPack, revoked); err != nil {
578 return protocol.ExitFailure
579 }
580 return protocol.ExitOK
581}