aboutsummaryrefslogtreecommitdiff
path: root/vendor/golang.org/x/crypto/ssh/channel.go
blob: 6d709b50be094cd19897e50866cac102e9d37893 (plain)
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
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ssh

import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"log"
	"sync"
)

const (
	minPacketLength = 9
	// channelMaxPacket contains the maximum number of bytes that will be
	// sent in a single packet. As per RFC 4253, section 6.1, 32k is also
	// the minimum.
	channelMaxPacket = 1 << 15
	// We follow OpenSSH here.
	channelWindowSize = 64 * channelMaxPacket
)

// NewChannel represents an incoming request to a channel. It must either be
// accepted for use by calling Accept, or rejected by calling Reject.
type NewChannel interface {
	// Accept accepts the channel creation request. It returns the Channel
	// and a Go channel containing SSH requests. The Go channel must be
	// serviced otherwise the Channel will hang.
	Accept() (Channel, <-chan *Request, error)

	// Reject rejects the channel creation request. After calling
	// this, no other methods on the Channel may be called.
	Reject(reason RejectionReason, message string) error

	// ChannelType returns the type of the channel, as supplied by the
	// client.
	ChannelType() string

	// ExtraData returns the arbitrary payload for this channel, as supplied
	// by the client. This data is specific to the channel type.
	ExtraData() []byte
}

// A Channel is an ordered, reliable, flow-controlled, duplex stream
// that is multiplexed over an SSH connection.
type Channel interface {
	// Read reads up to len(data) bytes from the channel.
	Read(data []byte) (int, error)

	// Write writes len(data) bytes to the channel.
	Write(data []byte) (int, error)

	// Close signals end of channel use. No data may be sent after this
	// call.
	Close() error

	// CloseWrite signals the end of sending in-band
	// data. Requests may still be sent, and the other side may
	// still send data
	CloseWrite() error

	// SendRequest sends a channel request.  If wantReply is true,
	// it will wait for a reply and return the result as a
	// boolean, otherwise the return value will be false. Channel
	// requests are out-of-band messages so they may be sent even
	// if the data stream is closed or blocked by flow control.
	// If the channel is closed before a reply is returned, io.EOF
	// is returned.
	SendRequest(name string, wantReply bool, payload []byte) (bool, error)

	// Stderr returns an io.ReadWriter that writes to this channel
	// with the extended data type set to stderr. Stderr may
	// safely be read and written from a different goroutine than
	// Read and Write respectively.
	Stderr() io.ReadWriter
}

// Request is a request sent outside of the normal stream of
// data. Requests can either be specific to an SSH channel, or they
// can be global.
type Request struct {
	Type      string
	WantReply bool
	Payload   []byte

	ch  *channel
	mux *mux
}

// Reply sends a response to a request. It must be called for all requests
// where WantReply is true and is a no-op otherwise. The payload argument is
// ignored for replies to channel-specific requests.
func (r *Request) Reply(ok bool, payload []byte) error {
	if !r.WantReply {
		return nil
	}

	if r.ch == nil {
		return r.mux.ackRequest(ok, payload)
	}

	return r.ch.ackRequest(ok)
}

// RejectionReason is an enumeration used when rejecting channel creation
// requests. See RFC 4254, section 5.1.
type RejectionReason uint32

const (
	Prohibited RejectionReason = iota + 1
	ConnectionFailed
	UnknownChannelType
	ResourceShortage
)

// String converts the rejection reason to human readable form.
func (r RejectionReason) String() string {
	switch r {
	case Prohibited:
		return "administratively prohibited"
	case ConnectionFailed:
		return "connect failed"
	case UnknownChannelType:
		return "unknown channel type"
	case ResourceShortage:
		return "resource shortage"
	}
	return fmt.Sprintf("unknown reason %d", int(r))
}

func min(a uint32, b int) uint32 {
	if a < uint32(b) {
		return a
	}
	return uint32(b)
}

type channelDirection uint8

const (
	channelInbound channelDirection = iota
	channelOutbound
)

// channel is an implementation of the Channel interface that works
// with the mux class.
type channel struct {
	// R/O after creation
	chanType          string
	extraData         []byte
	localId, remoteId uint32

	// maxIncomingPayload and maxRemotePayload are the maximum
	// payload sizes of normal and extended data packets for
	// receiving and sending, respectively. The wire packet will
	// be 9 or 13 bytes larger (excluding encryption overhead).
	maxIncomingPayload uint32
	maxRemotePayload   uint32

	mux *mux

	// decided is set to true if an accept or reject message has been sent
	// (for outbound channels) or received (for inbound channels).
	decided bool

	// direction contains either channelOutbound, for channels created
	// locally, or channelInbound, for channels created by the peer.
	direction channelDirection

	// Pending internal channel messages.
	msg chan interface{}

	// Since requests have no ID, there can be only one request
	// with WantReply=true outstanding.  This lock is held by a
	// goroutine that has such an outgoing request pending.
	sentRequestMu sync.Mutex

	incomingRequests chan *Request

	sentEOF bool

	// thread-safe data
	remoteWin  window
	pending    *buffer
	extPending *buffer

	// windowMu protects myWindow, the flow-control window.
	windowMu sync.Mutex
	myWindow uint32

	// writeMu serializes calls to mux.conn.writePacket() and
	// protects sentClose and packetPool. This mutex must be
	// different from windowMu, as writePacket can block if there
	// is a key exchange pending.
	writeMu   sync.Mutex
	sentClose bool

	// packetPool has a buffer for each extended channel ID to
	// save allocations during writes.
	packetPool map[uint32][]byte
}

// writePacket sends a packet. If the packet is a channel close, it updates
// sentClose. This method takes the lock c.writeMu.
func (c *channel) writePacket(packet []byte) error {
	c.writeMu.Lock()
	if c.sentClose {
		c.writeMu.Unlock()
		return io.EOF
	}
	c.sentClose = (packet[0] == msgChannelClose)
	err := c.mux.conn.writePacket(packet)
	c.writeMu.Unlock()
	return err
}

func (c *channel) sendMessage(msg interface{}) error {
	if debugMux {
		log.Printf("send(%d): %#v", c.mux.chanList.offset, msg)
	}

	p := Marshal(msg)
	binary.BigEndian.PutUint32(p[1:], c.remoteId)
	return c.writePacket(p)
}

// WriteExtended writes data to a specific extended stream. These streams are
// used, for example, for stderr.
func (c *channel) WriteExtended(data []byte, extendedCode uint32) (n int, err error) {
	if c.sentEOF {
		return 0, io.EOF
	}
	// 1 byte message type, 4 bytes remoteId, 4 bytes data length
	opCode := byte(msgChannelData)
	headerLength := uint32(9)
	if extendedCode > 0 {
		headerLength += 4
		opCode = msgChannelExtendedData
	}

	c.writeMu.Lock()
	packet := c.packetPool[extendedCode]
	// We don't remove the buffer from packetPool, so
	// WriteExtended calls from different goroutines will be
	// flagged as errors by the race detector.
	c.writeMu.Unlock()

	for len(data) > 0 {
		space := min(c.maxRemotePayload, len(data))
		if space, err = c.remoteWin.reserve(space); err != nil {
			return n, err
		}
		if want := headerLength + space; uint32(cap(packet)) < want {
			packet = make([]byte, want)
		} else {
			packet = packet[:want]
		}

		todo := data[:space]

		packet[0] = opCode
		binary.BigEndian.PutUint32(packet[1:], c.remoteId)
		if extendedCode > 0 {
			binary.BigEndian.PutUint32(packet[5:], uint32(extendedCode))
		}
		binary.BigEndian.PutUint32(packet[headerLength-4:], uint32(len(todo)))
		copy(packet[headerLength:], todo)
		if err = c.writePacket(packet); err != nil {
			return n, err
		}

		n += len(todo)
		data = data[len(todo):]
	}

	c.writeMu.Lock()
	c.packetPool[extendedCode] = packet
	c.writeMu.Unlock()

	return n, err
}

func (c *channel) handleData(packet []byte) error {
	headerLen := 9
	isExtendedData := packet[0] == msgChannelExtendedData
	if isExtendedData {
		headerLen = 13
	}
	if len(packet) < headerLen {
		// malformed data packet
		return parseError(packet[0])
	}

	var extended uint32
	if isExtendedData {
		extended = binary.BigEndian.Uint32(packet[5:])
	}

	length := binary.BigEndian.Uint32(packet[headerLen-4 : headerLen])
	if length == 0 {
		return nil
	}
	if length > c.maxIncomingPayload {
		// TODO(hanwen): should send Disconnect?
		return errors.New("ssh: incoming packet exceeds maximum payload size")
	}

	data := packet[headerLen:]
	if length != uint32(len(data)) {
		return errors.New("ssh: wrong packet length")
	}

	c.windowMu.Lock()
	if c.myWindow < length {
		c.windowMu.Unlock()
		// TODO(hanwen): should send Disconnect with reason?
		return errors.New("ssh: remote side wrote too much")
	}
	c.myWindow -= length
	c.windowMu.Unlock()

	if extended == 1 {
		c.extPending.write(data)
	} else if extended > 0 {
		// discard other extended data.
	} else {
		c.pending.write(data)
	}
	return nil
}

func (c *channel) adjustWindow(n uint32) error {
	c.windowMu.Lock()
	// Since myWindow is managed on our side, and can never exceed
	// the initial window setting, we don't worry about overflow.
	c.myWindow += uint32(n)
	c.windowMu.Unlock()
	return c.sendMessage(windowAdjustMsg{
		AdditionalBytes: uint32(n),
	})
}

func (c *channel) ReadExtended(data []byte, extended uint32) (n int, err error) {
	switch extended {
	case 1:
		n, err = c.extPending.Read(data)
	case 0:
		n, err = c.pending.Read(data)
	default:
		return 0, fmt.Errorf("ssh: extended code %d unimplemented", extended)
	}

	if n > 0 {
		err = c.adjustWindow(uint32(n))
		// sendWindowAdjust can return io.EOF if the remote
		// peer has closed the connection, however we want to
		// defer forwarding io.EOF to the caller of Read until
		// the buffer has been drained.
		if n > 0 && err == io.EOF {
			err = nil
		}
	}

	return n, err
}

func (c *channel) close() {
	c.pending.eof()
	c.extPending.eof()
	close(c.msg)
	close(c.incomingRequests)
	c.writeMu.Lock()
	// This is not necessary for a normal channel teardown, but if
	// there was another error, it is.
	c.sentClose = true
	c.writeMu.Unlock()
	// Unblock writers.
	c.remoteWin.close()
}

// responseMessageReceived is called when a success or failure message is
// received on a channel to check that such a message is reasonable for the
// given channel.
func (c *channel) responseMessageReceived() error {
	if c.direction == channelInbound {
		return errors.New("ssh: channel response message received on inbound channel")
	}
	if c.decided {
		return errors.New("ssh: duplicate response received for channel")
	}
	c.decided = true
	return nil
}

func (c *channel) handlePacket(packet []byte) error {
	switch packet[0] {
	case msgChannelData, msgChannelExtendedData:
		return c.handleData(packet)
	case msgChannelClose:
		c.sendMessage(channelCloseMsg{PeersId: c.remoteId})
		c.mux.chanList.remove(c.localId)
		c.close()
		return nil
	case msgChannelEOF:
		// RFC 4254 is mute on how EOF affects dataExt messages but
		// it is logical to signal EOF at the same time.
		c.extPending.eof()
		c.pending.eof()
		return nil
	}

	decoded, err := decode(packet)
	if err != nil {
		return err
	}

	switch msg := decoded.(type) {
	case *channelOpenFailureMsg:
		if err := c.responseMessageReceived(); err != nil {
			return err
		}
		c.mux.chanList.remove(msg.PeersId)
		c.msg <- msg
	case *channelOpenConfirmMsg:
		if err := c.responseMessageReceived(); err != nil {
			return err
		}
		if msg.MaxPacketSize < minPacketLength || msg.MaxPacketSize > 1<<31 {
			return fmt.Errorf("ssh: invalid MaxPacketSize %d from peer", msg.MaxPacketSize)
		}
		c.remoteId = msg.MyId
		c.maxRemotePayload = msg.MaxPacketSize
		c.remoteWin.add(msg.MyWindow)
		c.msg <- msg
	case *windowAdjustMsg:
		if !c.remoteWin.add(msg.AdditionalBytes) {
			return fmt.Errorf("ssh: invalid window update for %d bytes", msg.AdditionalBytes)
		}
	case *channelRequestMsg:
		req := Request{
			Type:      msg.Request,
			WantReply: msg.WantReply,
			Payload:   msg.RequestSpecificData,
			ch:        c,
		}

		c.incomingRequests <- &req
	default:
		c.msg <- msg
	}
	return nil
}

func (m *mux) newChannel(chanType string, direction channelDirection, extraData []byte) *channel {
	ch := &channel{
		remoteWin:        window{Cond: newCond()},
		myWindow:         channelWindowSize,
		pending:          newBuffer(),
		extPending:       newBuffer(),
		direction:        direction,
		incomingRequests: make(chan *Request, 16),
		msg:              make(chan interface{}, 16),
		chanType:         chanType,
		extraData:        extraData,
		mux:              m,
		packetPool:       make(map[uint32][]byte),
	}
	ch.localId = m.chanList.add(ch)
	return ch
}

var errUndecided = errors.New("ssh: must Accept or Reject channel")
var errDecidedAlready = errors.New("ssh: can call Accept or Reject only once")

type extChannel struct {
	code uint32
	ch   *channel
}

func (e *extChannel) Write(data []byte) (n int, err error) {
	return e.ch.WriteExtended(data, e.code)
}

func (e *extChannel) Read(data []byte) (n int, err error) {
	return e.ch.ReadExtended(data, e.code)
}

func (c *channel) Accept() (Channel, <-chan *Request, error) {
	if c.decided {
		return nil, nil, errDecidedAlready
	}
	c.maxIncomingPayload = channelMaxPacket
	confirm := channelOpenConfirmMsg{
		PeersId:       c.remoteId,
		MyId:          c.localId,
		MyWindow:      c.myWindow,
		MaxPacketSize: c.maxIncomingPayload,
	}
	c.decided = true
	if err := c.sendMessage(confirm); err != nil {
		return nil, nil, err
	}

	return c, c.incomingRequests, nil
}

func (ch *channel) Reject(reason RejectionReason, message string) error {
	if ch.decided {
		return errDecidedAlready
	}
	reject := channelOpenFailureMsg{
		PeersId:  ch.remoteId,
		Reason:   reason,
		Message:  message,
		Language: "en",
	}
	ch.decided = true
	return ch.sendMessage(reject)
}

func (ch *channel) Read(data []byte) (int, error) {
	if !ch.decided {
		return 0, errUndecided
	}
	return ch.ReadExtended(data, 0)
}

func (ch *channel) Write(data []byte) (int, error) {
	if !ch.decided {
		return 0, errUndecided
	}
	return ch.WriteExtended(data, 0)
}

func (ch *channel) CloseWrite() error {
	if !ch.decided {
		return errUndecided
	}
	ch.sentEOF = true
	return ch.sendMessage(channelEOFMsg{
		PeersId: ch.remoteId})
}

func (ch *channel) Close() error {
	if !ch.decided {
		return errUndecided
	}

	return ch.sendMessage(channelCloseMsg{
		PeersId: ch.remoteId})
}

// Extended returns an io.ReadWriter that sends and receives data on the given,
// SSH extended stream. Such streams are used, for example, for stderr.
func (ch *channel) Extended(code uint32) io.ReadWriter {
	if !ch.decided {
		return nil
	}
	return &extChannel{code, ch}
}

func (ch *channel) Stderr() io.ReadWriter {
	return ch.Extended(1)
}

func (ch *channel) SendRequest(name string, wantReply bool, payload []byte) (bool, error) {
	if !ch.decided {
		return false, errUndecided
	}

	if wantReply {
		ch.sentRequestMu.Lock()
		defer ch.sentRequestMu.Unlock()
	}

	msg := channelRequestMsg{
		PeersId:             ch.remoteId,
		Request:             name,
		WantReply:           wantReply,
		RequestSpecificData: payload,
	}

	if err := ch.sendMessage(msg); err != nil {
		return false, err
	}

	if wantReply {
		m, ok := (<-ch.msg)
		if !ok {
			return false, io.EOF
		}
		switch m.(type) {
		case *channelRequestFailureMsg:
			return false, nil
		case *channelRequestSuccessMsg:
			return true, nil
		default:
			return false, fmt.Errorf("ssh: unexpected response to channel request: %#v", m)
		}
	}

	return false, nil
}

// ackRequest either sends an ack or nack to the channel request.
func (ch *channel) ackRequest(ok bool) error {
	if !ch.decided {
		return errUndecided
	}

	var msg interface{}
	if !ok {
		msg = channelRequestFailureMsg{
			PeersId: ch.remoteId,
		}
	} else {
		msg = channelRequestSuccessMsg{
			PeersId: ch.remoteId,
		}
	}
	return ch.sendMessage(msg)
}

func (ch *channel) ChannelType() string {
	return ch.chanType
}

func (ch *channel) ExtraData() []byte {
	return ch.extraData
}