/
server.go
1354 lines (1248 loc) · 49.5 KB
/
server.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
// Copyright (C) 2019-2023 Nicola Murino
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, version 3.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
package sftpd
import (
"bytes"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"io"
"io/fs"
"net"
"os"
"path"
"path/filepath"
"runtime/debug"
"strings"
"sync"
"time"
"github.com/pkg/sftp"
"github.com/sftpgo/sdk/plugin/notifier"
"golang.org/x/crypto/ssh"
"github.com/drakkan/sftpgo/v2/internal/common"
"github.com/drakkan/sftpgo/v2/internal/dataprovider"
"github.com/drakkan/sftpgo/v2/internal/logger"
"github.com/drakkan/sftpgo/v2/internal/metric"
"github.com/drakkan/sftpgo/v2/internal/plugin"
"github.com/drakkan/sftpgo/v2/internal/util"
"github.com/drakkan/sftpgo/v2/internal/vfs"
)
const (
defaultPrivateRSAKeyName = "id_rsa"
defaultPrivateECDSAKeyName = "id_ecdsa"
defaultPrivateEd25519KeyName = "id_ed25519"
sourceAddressCriticalOption = "source-address"
kexDHGroupExchangeSHA1 = "diffie-hellman-group-exchange-sha1"
kexDHGroupExchangeSHA256 = "diffie-hellman-group-exchange-sha256"
)
var (
sftpExtensions = []string{"statvfs@openssh.com"}
supportedHostKeyAlgos = []string{
ssh.CertAlgoRSASHA512v01, ssh.CertAlgoRSASHA256v01,
ssh.CertAlgoRSAv01, ssh.CertAlgoDSAv01, ssh.CertAlgoECDSA256v01,
ssh.CertAlgoECDSA384v01, ssh.CertAlgoECDSA521v01, ssh.CertAlgoED25519v01,
ssh.KeyAlgoECDSA256, ssh.KeyAlgoECDSA384, ssh.KeyAlgoECDSA521,
ssh.KeyAlgoRSASHA512, ssh.KeyAlgoRSASHA256,
ssh.KeyAlgoRSA, ssh.KeyAlgoDSA,
ssh.KeyAlgoED25519,
}
preferredHostKeyAlgos = []string{
ssh.KeyAlgoRSASHA256, ssh.KeyAlgoRSASHA512,
ssh.KeyAlgoECDSA256, ssh.KeyAlgoECDSA384, ssh.KeyAlgoECDSA521,
ssh.KeyAlgoED25519,
}
supportedKexAlgos = []string{
"curve25519-sha256", "curve25519-sha256@libssh.org",
"ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
"diffie-hellman-group14-sha256", "diffie-hellman-group16-sha512",
"diffie-hellman-group18-sha512", "diffie-hellman-group14-sha1",
"diffie-hellman-group1-sha1",
}
preferredKexAlgos = []string{
"curve25519-sha256", "curve25519-sha256@libssh.org",
"ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
"diffie-hellman-group14-sha256",
}
supportedCiphers = []string{
"aes128-gcm@openssh.com", "aes256-gcm@openssh.com",
"chacha20-poly1305@openssh.com",
"aes128-ctr", "aes192-ctr", "aes256-ctr",
"aes128-cbc", "aes192-cbc", "aes256-cbc",
"3des-cbc",
"arcfour", "arcfour128", "arcfour256",
}
preferredCiphers = []string{
"aes128-gcm@openssh.com", "aes256-gcm@openssh.com",
"chacha20-poly1305@openssh.com",
"aes128-ctr", "aes192-ctr", "aes256-ctr",
}
supportedMACs = []string{
"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256",
"hmac-sha2-512-etm@openssh.com", "hmac-sha2-512",
"hmac-sha1", "hmac-sha1-96",
}
preferredMACs = []string{
"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256",
}
revokedCertManager = revokedCertificates{
certs: map[string]bool{},
}
sftpAuthError = newAuthenticationError(nil, "")
)
// Binding defines the configuration for a network listener
type Binding struct {
// The address to listen on. A blank value means listen on all available network interfaces.
Address string `json:"address" mapstructure:"address"`
// The port used for serving requests
Port int `json:"port" mapstructure:"port"`
// Apply the proxy configuration, if any, for this binding
ApplyProxyConfig bool `json:"apply_proxy_config" mapstructure:"apply_proxy_config"`
}
// GetAddress returns the binding address
func (b *Binding) GetAddress() string {
return fmt.Sprintf("%s:%d", b.Address, b.Port)
}
// IsValid returns true if the binding port is > 0
func (b *Binding) IsValid() bool {
return b.Port > 0
}
// HasProxy returns true if the proxy protocol is active for this binding
func (b *Binding) HasProxy() bool {
return b.ApplyProxyConfig && common.Config.ProxyProtocol > 0
}
// Configuration for the SFTP server
type Configuration struct {
// Identification string used by the server
Banner string `json:"banner" mapstructure:"banner"`
// Addresses and ports to bind to
Bindings []Binding `json:"bindings" mapstructure:"bindings"`
// Maximum number of authentication attempts permitted per connection.
// If set to a negative number, the number of attempts is unlimited.
// If set to zero, the number of attempts are limited to 6.
MaxAuthTries int `json:"max_auth_tries" mapstructure:"max_auth_tries"`
// HostKeys define the daemon's private host keys.
// Each host key can be defined as a path relative to the configuration directory or an absolute one.
// If empty or missing, the daemon will search or try to generate "id_rsa" and "id_ecdsa" host keys
// inside the configuration directory.
HostKeys []string `json:"host_keys" mapstructure:"host_keys"`
// HostCertificates defines public host certificates.
// Each certificate can be defined as a path relative to the configuration directory or an absolute one.
// Certificate's public key must match a private host key otherwise it will be silently ignored.
HostCertificates []string `json:"host_certificates" mapstructure:"host_certificates"`
// HostKeyAlgorithms lists the public key algorithms that the server will accept for host
// key authentication.
HostKeyAlgorithms []string `json:"host_key_algorithms" mapstructure:"host_key_algorithms"`
// Diffie-Hellman moduli files.
// Each moduli file can be defined as a path relative to the configuration directory or an absolute one.
// If set and valid, "diffie-hellman-group-exchange-sha256" and "diffie-hellman-group-exchange-sha1" KEX algorithms
// will be available, `diffie-hellman-group-exchange-sha256` will be enabled by default if you
// don't explicitly set KEXs
Moduli []string `json:"moduli" mapstructure:"moduli"`
// KexAlgorithms specifies the available KEX (Key Exchange) algorithms in
// preference order.
KexAlgorithms []string `json:"kex_algorithms" mapstructure:"kex_algorithms"`
// Ciphers specifies the ciphers allowed
Ciphers []string `json:"ciphers" mapstructure:"ciphers"`
// MACs Specifies the available MAC (message authentication code) algorithms
// in preference order
MACs []string `json:"macs" mapstructure:"macs"`
// TrustedUserCAKeys specifies a list of public keys paths of certificate authorities
// that are trusted to sign user certificates for authentication.
// The paths can be absolute or relative to the configuration directory
TrustedUserCAKeys []string `json:"trusted_user_ca_keys" mapstructure:"trusted_user_ca_keys"`
// Path to a file containing the revoked user certificates.
// This file must contain a JSON list with the public key fingerprints of the revoked certificates.
// Example content:
// ["SHA256:bsBRHC/xgiqBJdSuvSTNpJNLTISP/G356jNMCRYC5Es","SHA256:119+8cL/HH+NLMawRsJx6CzPF1I3xC+jpM60bQHXGE8"]
RevokedUserCertsFile string `json:"revoked_user_certs_file" mapstructure:"revoked_user_certs_file"`
// LoginBannerFile the contents of the specified file, if any, are sent to
// the remote user before authentication is allowed.
LoginBannerFile string `json:"login_banner_file" mapstructure:"login_banner_file"`
// List of enabled SSH commands.
// We support the following SSH commands:
// - "scp". SCP is an experimental feature, we have our own SCP implementation since
// we can't rely on scp system command to proper handle permissions, quota and
// user's home dir restrictions.
// The SCP protocol is quite simple but there is no official docs about it,
// so we need more testing and feedbacks before enabling it by default.
// We may not handle some borderline cases or have sneaky bugs.
// Please do accurate tests yourself before enabling SCP and let us known
// if something does not work as expected for your use cases.
// SCP between two remote hosts is supported using the `-3` scp option.
// - "md5sum", "sha1sum", "sha256sum", "sha384sum", "sha512sum". Useful to check message
// digests for uploaded files. These commands are implemented inside SFTPGo so they
// work even if the matching system commands are not available, for example on Windows.
// - "cd", "pwd". Some mobile SFTP clients does not support the SFTP SSH_FXP_REALPATH and so
// they use "cd" and "pwd" SSH commands to get the initial directory.
// Currently `cd` do nothing and `pwd` always returns the "/" path.
//
// The following SSH commands are enabled by default: "md5sum", "sha1sum", "cd", "pwd".
// "*" enables all supported SSH commands.
EnabledSSHCommands []string `json:"enabled_ssh_commands" mapstructure:"enabled_ssh_commands"`
// KeyboardInteractiveAuthentication specifies whether keyboard interactive authentication is allowed.
// If no keyboard interactive hook or auth plugin is defined the default is to prompt for the user password and then the
// one time authentication code, if defined.
KeyboardInteractiveAuthentication bool `json:"keyboard_interactive_authentication" mapstructure:"keyboard_interactive_authentication"`
// Absolute path to an external program or an HTTP URL to invoke for keyboard interactive authentication.
// Leave empty to disable this authentication mode.
KeyboardInteractiveHook string `json:"keyboard_interactive_auth_hook" mapstructure:"keyboard_interactive_auth_hook"`
// PasswordAuthentication specifies whether password authentication is allowed.
PasswordAuthentication bool `json:"password_authentication" mapstructure:"password_authentication"`
// Virtual root folder prefix to include in all file operations (ex: /files).
// The virtual paths used for per-directory permissions, file patterns etc. must not include the folder prefix.
// The prefix is only applied to SFTP requests, SCP and other SSH commands will be automatically disabled if
// you configure a prefix.
// This setting can help some migrations from OpenSSH. It is not recommended for general usage.
FolderPrefix string `json:"folder_prefix" mapstructure:"folder_prefix"`
certChecker *ssh.CertChecker
parsedUserCAKeys []ssh.PublicKey
}
type authenticationError struct {
err error
loginMethod string
}
func (e *authenticationError) Error() string {
return fmt.Sprintf("Authentication error: %v", e.err)
}
// Is reports if target matches
func (e *authenticationError) Is(target error) bool {
_, ok := target.(*authenticationError)
return ok
}
// Unwrap returns the wrapped error
func (e *authenticationError) Unwrap() error {
return e.err
}
func (e *authenticationError) getLoginMethod() string {
return e.loginMethod
}
func newAuthenticationError(err error, loginMethod string) *authenticationError {
return &authenticationError{err: err, loginMethod: loginMethod}
}
// ShouldBind returns true if there is at least a valid binding
func (c *Configuration) ShouldBind() bool {
for _, binding := range c.Bindings {
if binding.IsValid() {
return true
}
}
return false
}
func (c *Configuration) getServerConfig() *ssh.ServerConfig {
serverConfig := &ssh.ServerConfig{
NoClientAuth: false,
MaxAuthTries: c.MaxAuthTries,
PublicKeyCallback: func(conn ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
sp, err := c.validatePublicKeyCredentials(conn, pubKey)
if err == ssh.ErrPartialSuccess {
return sp, err
}
if err != nil {
return nil, newAuthenticationError(fmt.Errorf("could not validate public key credentials: %w", err),
dataprovider.SSHLoginMethodPublicKey)
}
return sp, nil
},
NextAuthMethodsCallback: func(conn ssh.ConnMetadata) []string {
var nextMethods []string
user, err := dataprovider.GetUserWithGroupSettings(conn.User(), "")
if err == nil {
nextMethods = user.GetNextAuthMethods(conn.PartialSuccessMethods(), c.PasswordAuthentication)
}
return nextMethods
},
ServerVersion: fmt.Sprintf("SSH-2.0-%s", c.Banner),
}
if c.PasswordAuthentication {
serverConfig.PasswordCallback = func(conn ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
sp, err := c.validatePasswordCredentials(conn, pass)
if err != nil {
return nil, newAuthenticationError(fmt.Errorf("could not validate password credentials: %w", err),
dataprovider.SSHLoginMethodPassword)
}
return sp, nil
}
serviceStatus.Authentications = append(serviceStatus.Authentications, dataprovider.LoginMethodPassword)
}
serviceStatus.Authentications = append(serviceStatus.Authentications, dataprovider.SSHLoginMethodPublicKey)
return serverConfig
}
func (c *Configuration) updateSupportedAuthentications() {
serviceStatus.Authentications = util.RemoveDuplicates(serviceStatus.Authentications, false)
if util.Contains(serviceStatus.Authentications, dataprovider.LoginMethodPassword) &&
util.Contains(serviceStatus.Authentications, dataprovider.SSHLoginMethodPublicKey) {
serviceStatus.Authentications = append(serviceStatus.Authentications, dataprovider.SSHLoginMethodKeyAndPassword)
}
if util.Contains(serviceStatus.Authentications, dataprovider.SSHLoginMethodKeyboardInteractive) &&
util.Contains(serviceStatus.Authentications, dataprovider.SSHLoginMethodPublicKey) {
serviceStatus.Authentications = append(serviceStatus.Authentications, dataprovider.SSHLoginMethodKeyAndKeyboardInt)
}
}
func (c *Configuration) loadFromProvider() error {
configs, err := dataprovider.GetConfigs()
if err != nil {
return fmt.Errorf("unable to load config from provider: %w", err)
}
configs.SetNilsToEmpty()
if len(configs.SFTPD.HostKeyAlgos) > 0 {
if len(c.HostKeyAlgorithms) == 0 {
c.HostKeyAlgorithms = preferredHostKeyAlgos
}
c.HostKeyAlgorithms = append(c.HostKeyAlgorithms, configs.SFTPD.HostKeyAlgos...)
}
c.Moduli = append(c.Moduli, configs.SFTPD.Moduli...)
if len(configs.SFTPD.KexAlgorithms) > 0 {
if len(c.KexAlgorithms) == 0 {
c.KexAlgorithms = preferredKexAlgos
}
c.KexAlgorithms = append(c.KexAlgorithms, configs.SFTPD.KexAlgorithms...)
}
if len(configs.SFTPD.Ciphers) > 0 {
if len(c.Ciphers) == 0 {
c.Ciphers = preferredCiphers
}
c.Ciphers = append(c.Ciphers, configs.SFTPD.Ciphers...)
}
if len(configs.SFTPD.MACs) > 0 {
if len(c.MACs) == 0 {
c.MACs = preferredMACs
}
c.MACs = append(c.MACs, configs.SFTPD.MACs...)
}
return nil
}
// Initialize the SFTP server and add a persistent listener to handle inbound SFTP connections.
func (c *Configuration) Initialize(configDir string) error {
if err := c.loadFromProvider(); err != nil {
return fmt.Errorf("unable to load configs from provider: %w", err)
}
serviceStatus = ServiceStatus{}
serverConfig := c.getServerConfig()
if !c.ShouldBind() {
return common.ErrNoBinding
}
c.loadModuli(configDir)
sftp.SetSFTPExtensions(sftpExtensions...) //nolint:errcheck // we configure valid SFTP Extensions so we cannot get an error
if err := c.configureSecurityOptions(serverConfig); err != nil {
return err
}
if err := c.checkAndLoadHostKeys(configDir, serverConfig); err != nil {
serviceStatus.HostKeys = nil
return err
}
if err := c.initializeCertChecker(configDir); err != nil {
return err
}
c.configureKeyboardInteractiveAuth(serverConfig)
c.configureLoginBanner(serverConfig, configDir)
c.checkSSHCommands()
c.checkFolderPrefix()
exitChannel := make(chan error, 1)
serviceStatus.Bindings = nil
for _, binding := range c.Bindings {
if !binding.IsValid() {
continue
}
serviceStatus.Bindings = append(serviceStatus.Bindings, binding)
go func(binding Binding) {
addr := binding.GetAddress()
util.CheckTCP4Port(binding.Port)
listener, err := net.Listen("tcp", addr)
if err != nil {
logger.Warn(logSender, "", "error starting listener on address %v: %v", addr, err)
exitChannel <- err
return
}
if binding.ApplyProxyConfig && common.Config.ProxyProtocol > 0 {
proxyListener, err := common.Config.GetProxyListener(listener)
if err != nil {
logger.Warn(logSender, "", "error enabling proxy listener: %v", err)
exitChannel <- err
return
}
listener = proxyListener
}
exitChannel <- c.serve(listener, serverConfig)
}(binding)
}
serviceStatus.IsActive = true
serviceStatus.SSHCommands = c.EnabledSSHCommands
c.updateSupportedAuthentications()
return <-exitChannel
}
func (c *Configuration) serve(listener net.Listener, serverConfig *ssh.ServerConfig) error {
logger.Info(logSender, "", "server listener registered, address: %s", listener.Addr().String())
var tempDelay time.Duration // how long to sleep on accept failure
for {
conn, err := listener.Accept()
if err != nil {
// see https://github.com/golang/go/blob/4aa1efed4853ea067d665a952eee77c52faac774/src/net/http/server.go#L3046
if ne, ok := err.(net.Error); ok && ne.Temporary() { //nolint:staticcheck
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
logger.Warn(logSender, "", "accept error: %v; retrying in %v", err, tempDelay)
time.Sleep(tempDelay)
continue
}
logger.Warn(logSender, "", "unrecoverable accept error: %v", err)
return err
}
tempDelay = 0
go c.AcceptInboundConnection(conn, serverConfig)
}
}
func (c *Configuration) configureSecurityOptions(serverConfig *ssh.ServerConfig) error {
if len(c.HostKeyAlgorithms) == 0 {
c.HostKeyAlgorithms = preferredHostKeyAlgos
} else {
c.HostKeyAlgorithms = util.RemoveDuplicates(c.HostKeyAlgorithms, true)
}
for _, hostKeyAlgo := range c.HostKeyAlgorithms {
if !util.Contains(supportedHostKeyAlgos, hostKeyAlgo) {
return fmt.Errorf("unsupported host key algorithm %q", hostKeyAlgo)
}
}
if len(c.KexAlgorithms) > 0 {
hasDHGroupKEX := util.Contains(supportedKexAlgos, kexDHGroupExchangeSHA256)
if !hasDHGroupKEX {
c.KexAlgorithms = util.Remove(c.KexAlgorithms, kexDHGroupExchangeSHA1)
c.KexAlgorithms = util.Remove(c.KexAlgorithms, kexDHGroupExchangeSHA256)
}
c.KexAlgorithms = util.RemoveDuplicates(c.KexAlgorithms, true)
for _, kex := range c.KexAlgorithms {
if !util.Contains(supportedKexAlgos, kex) {
return fmt.Errorf("unsupported key-exchange algorithm %q", kex)
}
}
serverConfig.KeyExchanges = c.KexAlgorithms
serviceStatus.KexAlgorithms = c.KexAlgorithms
} else {
serviceStatus.KexAlgorithms = preferredKexAlgos
}
if len(c.Ciphers) > 0 {
c.Ciphers = util.RemoveDuplicates(c.Ciphers, true)
for _, cipher := range c.Ciphers {
if !util.Contains(supportedCiphers, cipher) {
return fmt.Errorf("unsupported cipher %q", cipher)
}
}
serverConfig.Ciphers = c.Ciphers
serviceStatus.Ciphers = c.Ciphers
} else {
serviceStatus.Ciphers = preferredCiphers
}
if len(c.MACs) > 0 {
c.MACs = util.RemoveDuplicates(c.MACs, true)
for _, mac := range c.MACs {
if !util.Contains(supportedMACs, mac) {
return fmt.Errorf("unsupported MAC algorithm %q", mac)
}
}
serverConfig.MACs = c.MACs
serviceStatus.MACs = c.MACs
} else {
serviceStatus.MACs = preferredMACs
}
return nil
}
func (c *Configuration) configureLoginBanner(serverConfig *ssh.ServerConfig, configDir string) {
if len(c.LoginBannerFile) > 0 {
bannerFilePath := c.LoginBannerFile
if !filepath.IsAbs(bannerFilePath) {
bannerFilePath = filepath.Join(configDir, bannerFilePath)
}
bannerContent, err := os.ReadFile(bannerFilePath)
if err == nil {
banner := string(bannerContent)
serverConfig.BannerCallback = func(conn ssh.ConnMetadata) string {
return banner
}
} else {
logger.WarnToConsole("unable to read SFTPD login banner file: %v", err)
logger.Warn(logSender, "", "unable to read login banner file: %v", err)
}
}
}
func (c *Configuration) configureKeyboardInteractiveAuth(serverConfig *ssh.ServerConfig) {
if !c.KeyboardInteractiveAuthentication {
return
}
if c.KeyboardInteractiveHook != "" {
if !strings.HasPrefix(c.KeyboardInteractiveHook, "http") {
if !filepath.IsAbs(c.KeyboardInteractiveHook) {
logger.WarnToConsole("invalid keyboard interactive authentication program: %q must be an absolute path",
c.KeyboardInteractiveHook)
logger.Warn(logSender, "", "invalid keyboard interactive authentication program: %q must be an absolute path",
c.KeyboardInteractiveHook)
return
}
_, err := os.Stat(c.KeyboardInteractiveHook)
if err != nil {
logger.WarnToConsole("invalid keyboard interactive authentication program:: %v", err)
logger.Warn(logSender, "", "invalid keyboard interactive authentication program:: %v", err)
return
}
}
}
serverConfig.KeyboardInteractiveCallback = func(conn ssh.ConnMetadata, client ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error) {
sp, err := c.validateKeyboardInteractiveCredentials(conn, client)
if err != nil {
return nil, newAuthenticationError(fmt.Errorf("could not validate keyboard interactive credentials: %w", err),
dataprovider.SSHLoginMethodKeyboardInteractive)
}
return sp, nil
}
serviceStatus.Authentications = append(serviceStatus.Authentications, dataprovider.SSHLoginMethodKeyboardInteractive)
}
// AcceptInboundConnection handles an inbound connection to the server instance and determines if the request should be served or not.
func (c *Configuration) AcceptInboundConnection(conn net.Conn, config *ssh.ServerConfig) {
defer func() {
if r := recover(); r != nil {
logger.Error(logSender, "", "panic in AcceptInboundConnection: %q stack trace: %v", r, string(debug.Stack()))
}
}()
ipAddr := util.GetIPFromRemoteAddress(conn.RemoteAddr().String())
common.Connections.AddClientConnection(ipAddr)
defer common.Connections.RemoveClientConnection(ipAddr)
if !canAcceptConnection(ipAddr) {
conn.Close()
return
}
// Before beginning a handshake must be performed on the incoming net.Conn
// we'll set a Deadline for handshake to complete, the default is 2 minutes as OpenSSH
conn.SetDeadline(time.Now().Add(handshakeTimeout)) //nolint:errcheck
sconn, chans, reqs, err := ssh.NewServerConn(conn, config)
if err != nil {
logger.Debug(logSender, "", "failed to accept an incoming connection from ip %q: %v", ipAddr, err)
checkAuthError(ipAddr, err)
return
}
// handshake completed so remove the deadline, we'll use IdleTimeout configuration from now on
conn.SetDeadline(time.Time{}) //nolint:errcheck
go ssh.DiscardRequests(reqs)
defer conn.Close()
var user dataprovider.User
// Unmarshal cannot fails here and even if it fails we'll have a user with no permissions
json.Unmarshal([]byte(sconn.Permissions.Extensions["sftpgo_user"]), &user) //nolint:errcheck
loginType := sconn.Permissions.Extensions["sftpgo_login_method"]
connectionID := hex.EncodeToString(sconn.SessionID())
defer user.CloseFs() //nolint:errcheck
if err = user.CheckFsRoot(connectionID); err != nil {
logger.Warn(logSender, connectionID, "unable to check fs root for user %q: %v", user.Username, err)
go discardAllChannels(chans, "invalid root fs", connectionID)
return
}
logger.Log(logger.LevelInfo, common.ProtocolSSH, connectionID,
"User %q logged in with %q, from ip %q, client version %q", user.Username, loginType,
ipAddr, string(sconn.ClientVersion()))
dataprovider.UpdateLastLogin(&user)
sshConnection := common.NewSSHConnection(connectionID, conn)
common.Connections.AddSSHConnection(sshConnection)
defer common.Connections.RemoveSSHConnection(connectionID)
channelCounter := int64(0)
for newChannel := range chans {
// If its not a session channel we just move on because its not something we
// know how to handle at this point.
if newChannel.ChannelType() != "session" {
logger.Log(logger.LevelDebug, common.ProtocolSSH, connectionID, "received an unknown channel type: %v",
newChannel.ChannelType())
newChannel.Reject(ssh.UnknownChannelType, "unknown channel type") //nolint:errcheck
continue
}
channel, requests, err := newChannel.Accept()
if err != nil {
logger.Log(logger.LevelWarn, common.ProtocolSSH, connectionID, "could not accept a channel: %v", err)
continue
}
channelCounter++
sshConnection.UpdateLastActivity()
// Channels have a type that is dependent on the protocol. For SFTP this is "subsystem"
// with a payload that (should) be "sftp". Discard anything else we receive ("pty", "shell", etc)
go func(in <-chan *ssh.Request, counter int64) {
for req := range in {
ok := false
connID := fmt.Sprintf("%s_%d", connectionID, counter)
switch req.Type {
case "subsystem":
if string(req.Payload[4:]) == "sftp" {
ok = true
connection := &Connection{
BaseConnection: common.NewBaseConnection(connID, common.ProtocolSFTP, conn.LocalAddr().String(),
conn.RemoteAddr().String(), user),
ClientVersion: string(sconn.ClientVersion()),
RemoteAddr: conn.RemoteAddr(),
LocalAddr: conn.LocalAddr(),
channel: channel,
folderPrefix: c.FolderPrefix,
}
go c.handleSftpConnection(channel, connection)
}
case "exec":
// protocol will be set later inside processSSHCommand it could be SSH or SCP
connection := Connection{
BaseConnection: common.NewBaseConnection(connID, "sshd_exec", conn.LocalAddr().String(),
conn.RemoteAddr().String(), user),
ClientVersion: string(sconn.ClientVersion()),
RemoteAddr: conn.RemoteAddr(),
LocalAddr: conn.LocalAddr(),
channel: channel,
folderPrefix: c.FolderPrefix,
}
ok = processSSHCommand(req.Payload, &connection, c.EnabledSSHCommands)
}
if req.WantReply {
req.Reply(ok, nil) //nolint:errcheck
}
}
}(requests, channelCounter)
}
}
func (c *Configuration) handleSftpConnection(channel ssh.Channel, connection *Connection) {
defer func() {
if r := recover(); r != nil {
logger.Error(logSender, "", "panic in handleSftpConnection: %q stack trace: %v", r, string(debug.Stack()))
}
}()
if err := common.Connections.Add(connection); err != nil {
errClose := connection.Disconnect()
logger.Info(logSender, "", "unable to add connection: %v, close err: %v", err, errClose)
return
}
defer common.Connections.Remove(connection.GetID())
// Create the server instance for the channel using the handler we created above.
server := sftp.NewRequestServer(channel, c.createHandlers(connection), sftp.WithRSAllocator(),
sftp.WithStartDirectory(connection.User.Filters.StartDirectory))
defer server.Close()
if err := server.Serve(); errors.Is(err, io.EOF) {
exitStatus := sshSubsystemExitStatus{Status: uint32(0)}
_, err = channel.SendRequest("exit-status", false, ssh.Marshal(&exitStatus))
connection.Log(logger.LevelInfo, "connection closed, sent exit status %+v error: %v", exitStatus, err)
} else if err != nil {
connection.Log(logger.LevelError, "connection closed with error: %v", err)
}
}
func (c *Configuration) createHandlers(connection *Connection) sftp.Handlers {
if c.FolderPrefix != "" {
prefixMiddleware := newPrefixMiddleware(c.FolderPrefix, connection)
return sftp.Handlers{
FileGet: prefixMiddleware,
FilePut: prefixMiddleware,
FileCmd: prefixMiddleware,
FileList: prefixMiddleware,
}
}
return sftp.Handlers{
FileGet: connection,
FilePut: connection,
FileCmd: connection,
FileList: connection,
}
}
func canAcceptConnection(ip string) bool {
if common.IsBanned(ip, common.ProtocolSSH) {
logger.Log(logger.LevelDebug, common.ProtocolSSH, "", "connection refused, ip %q is banned", ip)
return false
}
if err := common.Connections.IsNewConnectionAllowed(ip, common.ProtocolSSH); err != nil {
logger.Log(logger.LevelDebug, common.ProtocolSSH, "", "connection not allowed from ip %q: %v", ip, err)
return false
}
_, err := common.LimitRate(common.ProtocolSSH, ip)
if err != nil {
return false
}
if err := common.Config.ExecutePostConnectHook(ip, common.ProtocolSSH); err != nil {
return false
}
return true
}
func discardAllChannels(in <-chan ssh.NewChannel, message, connectionID string) {
for req := range in {
err := req.Reject(ssh.ConnectionFailed, message)
logger.Debug(logSender, connectionID, "discarded channel request, message %q err: %v", message, err)
}
}
func checkAuthError(ip string, err error) {
if authErrors, ok := err.(*ssh.ServerAuthError); ok {
// check public key auth errors here
for _, err := range authErrors.Errors {
var sftpAuthErr *authenticationError
if errors.As(err, &sftpAuthErr) {
if sftpAuthErr.getLoginMethod() == dataprovider.SSHLoginMethodPublicKey {
event := common.HostEventLoginFailed
logEv := notifier.LogEventTypeLoginFailed
if errors.Is(err, util.ErrNotFound) {
event = common.HostEventUserNotFound
logEv = notifier.LogEventTypeLoginNoUser
}
common.AddDefenderEvent(ip, common.ProtocolSSH, event)
plugin.Handler.NotifyLogEvent(logEv, common.ProtocolSSH, "", ip, "", err)
return
}
}
}
} else {
logger.ConnectionFailedLog("", ip, dataprovider.LoginMethodNoAuthTried, common.ProtocolSSH, err.Error())
metric.AddNoAuthTried()
common.AddDefenderEvent(ip, common.ProtocolSSH, common.HostEventNoLoginTried)
dataprovider.ExecutePostLoginHook(&dataprovider.User{}, dataprovider.LoginMethodNoAuthTried, ip, common.ProtocolSSH, err)
logEv := notifier.LogEventTypeNoLoginTried
if errors.Is(err, ssh.ErrNoCommonAlgo) {
logEv = notifier.LogEventTypeNotNegotiated
}
plugin.Handler.NotifyLogEvent(logEv, common.ProtocolSSH, "", ip, "", err)
}
}
func loginUser(user *dataprovider.User, loginMethod, publicKey string, conn ssh.ConnMetadata) (*ssh.Permissions, error) {
connectionID := ""
if conn != nil {
connectionID = hex.EncodeToString(conn.SessionID())
}
if !filepath.IsAbs(user.HomeDir) {
logger.Warn(logSender, connectionID, "user %q has an invalid home dir: %q. Home dir must be an absolute path, login not allowed",
user.Username, user.HomeDir)
return nil, fmt.Errorf("cannot login user with invalid home dir: %q", user.HomeDir)
}
if util.Contains(user.Filters.DeniedProtocols, common.ProtocolSSH) {
logger.Info(logSender, connectionID, "cannot login user %q, protocol SSH is not allowed", user.Username)
return nil, fmt.Errorf("protocol SSH is not allowed for user %q", user.Username)
}
if user.MaxSessions > 0 {
activeSessions := common.Connections.GetActiveSessions(user.Username)
if activeSessions >= user.MaxSessions {
logger.Info(logSender, "", "authentication refused for user: %q, too many open sessions: %v/%v", user.Username,
activeSessions, user.MaxSessions)
return nil, fmt.Errorf("too many open sessions: %v", activeSessions)
}
}
if !user.IsLoginMethodAllowed(loginMethod, common.ProtocolSSH, conn.PartialSuccessMethods()) {
logger.Info(logSender, connectionID, "cannot login user %q, login method %q is not allowed",
user.Username, loginMethod)
return nil, fmt.Errorf("login method %q is not allowed for user %q", loginMethod, user.Username)
}
if user.MustSetSecondFactorForProtocol(common.ProtocolSSH) {
logger.Info(logSender, connectionID, "cannot login user %q, second factor authentication is not set",
user.Username)
return nil, fmt.Errorf("second factor authentication is not set for user %q", user.Username)
}
remoteAddr := conn.RemoteAddr().String()
if !user.IsLoginFromAddrAllowed(remoteAddr) {
logger.Info(logSender, connectionID, "cannot login user %q, remote address is not allowed: %v",
user.Username, remoteAddr)
return nil, fmt.Errorf("login for user %q is not allowed from this address: %v", user.Username, remoteAddr)
}
json, err := json.Marshal(user)
if err != nil {
logger.Warn(logSender, connectionID, "error serializing user info: %v, authentication rejected", err)
return nil, err
}
if publicKey != "" {
loginMethod = fmt.Sprintf("%v: %v", loginMethod, publicKey)
}
p := &ssh.Permissions{}
p.Extensions = make(map[string]string)
p.Extensions["sftpgo_user"] = string(json)
p.Extensions["sftpgo_login_method"] = loginMethod
return p, nil
}
func (c *Configuration) checkSSHCommands() {
if util.Contains(c.EnabledSSHCommands, "*") {
c.EnabledSSHCommands = GetSupportedSSHCommands()
return
}
sshCommands := []string{}
for _, command := range c.EnabledSSHCommands {
command = strings.TrimSpace(command)
if util.Contains(supportedSSHCommands, command) {
sshCommands = append(sshCommands, command)
} else {
logger.Warn(logSender, "", "unsupported ssh command: %q ignored", command)
logger.WarnToConsole("unsupported ssh command: %q ignored", command)
}
}
c.EnabledSSHCommands = sshCommands
logger.Debug(logSender, "", "enabled SSH commands %v", c.EnabledSSHCommands)
}
func (c *Configuration) checkFolderPrefix() {
if c.FolderPrefix != "" {
c.FolderPrefix = path.Join("/", c.FolderPrefix)
if c.FolderPrefix == "/" {
c.FolderPrefix = ""
}
}
if c.FolderPrefix != "" {
c.EnabledSSHCommands = nil
logger.Debug(logSender, "", "folder prefix %q configured, SSH commands are disabled", c.FolderPrefix)
}
}
func (c *Configuration) generateDefaultHostKeys(configDir string) error {
var err error
defaultHostKeys := []string{defaultPrivateRSAKeyName, defaultPrivateECDSAKeyName, defaultPrivateEd25519KeyName}
for _, k := range defaultHostKeys {
autoFile := filepath.Join(configDir, k)
if _, err = os.Stat(autoFile); errors.Is(err, fs.ErrNotExist) {
logger.Info(logSender, "", "No host keys configured and %q does not exist; try to create a new host key", autoFile)
logger.InfoToConsole("No host keys configured and %q does not exist; try to create a new host key", autoFile)
if k == defaultPrivateRSAKeyName {
err = util.GenerateRSAKeys(autoFile)
} else if k == defaultPrivateECDSAKeyName {
err = util.GenerateECDSAKeys(autoFile)
} else {
err = util.GenerateEd25519Keys(autoFile)
}
if err != nil {
logger.Warn(logSender, "", "error creating host key %q: %v", autoFile, err)
logger.WarnToConsole("error creating host key %q: %v", autoFile, err)
return err
}
}
c.HostKeys = append(c.HostKeys, k)
}
return err
}
func (c *Configuration) checkHostKeyAutoGeneration(configDir string) error {
for _, k := range c.HostKeys {
k = strings.TrimSpace(k)
if filepath.IsAbs(k) {
if _, err := os.Stat(k); errors.Is(err, fs.ErrNotExist) {
keyName := filepath.Base(k)
switch keyName {
case defaultPrivateRSAKeyName:
logger.Info(logSender, "", "try to create non-existent host key %q", k)
logger.InfoToConsole("try to create non-existent host key %q", k)
err = util.GenerateRSAKeys(k)
if err != nil {
logger.Warn(logSender, "", "error creating host key %q: %v", k, err)
logger.WarnToConsole("error creating host key %q: %v", k, err)
return err
}
case defaultPrivateECDSAKeyName:
logger.Info(logSender, "", "try to create non-existent host key %q", k)
logger.InfoToConsole("try to create non-existent host key %q", k)
err = util.GenerateECDSAKeys(k)
if err != nil {
logger.Warn(logSender, "", "error creating host key %q: %v", k, err)
logger.WarnToConsole("error creating host key %q: %v", k, err)
return err
}
case defaultPrivateEd25519KeyName:
logger.Info(logSender, "", "try to create non-existent host key %q", k)
logger.InfoToConsole("try to create non-existent host key %q", k)
err = util.GenerateEd25519Keys(k)
if err != nil {
logger.Warn(logSender, "", "error creating host key %q: %v", k, err)
logger.WarnToConsole("error creating host key %q: %v", k, err)
return err
}
default:
logger.Warn(logSender, "", "non-existent host key %q will not be created", k)
logger.WarnToConsole("non-existent host key %q will not be created", k)
}
}
}
}
if len(c.HostKeys) == 0 {
if err := c.generateDefaultHostKeys(configDir); err != nil {
return err
}
}
return nil
}
func (c *Configuration) loadModuli(configDir string) {
supportedKexAlgos = util.Remove(supportedKexAlgos, kexDHGroupExchangeSHA1)
supportedKexAlgos = util.Remove(supportedKexAlgos, kexDHGroupExchangeSHA256)
preferredKexAlgos = util.Remove(preferredKexAlgos, kexDHGroupExchangeSHA256)
c.Moduli = util.RemoveDuplicates(c.Moduli, false)
for _, m := range c.Moduli {
m = strings.TrimSpace(m)
if !util.IsFileInputValid(m) {
logger.Warn(logSender, "", "unable to load invalid moduli file %q", m)
logger.WarnToConsole("unable to load invalid host moduli file %q", m)
continue
}
if !filepath.IsAbs(m) {
m = filepath.Join(configDir, m)
}
logger.Info(logSender, "", "loading moduli file %q", m)
if err := ssh.ParseModuli(m); err != nil {
logger.Warn(logSender, "", "ignoring moduli file %q, error: %v", m, err)
continue
}
if !util.Contains(supportedKexAlgos, kexDHGroupExchangeSHA1) {
supportedKexAlgos = append(supportedKexAlgos, kexDHGroupExchangeSHA1)
}
if !util.Contains(supportedKexAlgos, kexDHGroupExchangeSHA256) {
supportedKexAlgos = append(supportedKexAlgos, kexDHGroupExchangeSHA256)
}
if !util.Contains(preferredKexAlgos, kexDHGroupExchangeSHA256) {
preferredKexAlgos = append(preferredKexAlgos, kexDHGroupExchangeSHA256)
}
}
}
func (c *Configuration) getHostKeyAlgorithms(keyFormat string) []string {
var algos []string
for _, algo := range algorithmsForKeyFormat(keyFormat) {
if util.Contains(c.HostKeyAlgorithms, algo) {
algos = append(algos, algo)
}
}
return algos
}
// If no host keys are defined we try to use or generate the default ones.
func (c *Configuration) checkAndLoadHostKeys(configDir string, serverConfig *ssh.ServerConfig) error { //nolint:gocyclo
if err := c.checkHostKeyAutoGeneration(configDir); err != nil {
return err
}
hostCertificates, err := c.loadHostCertificates(configDir)