ssh/util.go at main · devsy-org/ssh · GitHub

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
package ssh

import (
	"crypto/rand"
	"crypto/rsa"
	"encoding/binary"

	"golang.org/x/crypto/ssh"
)

func generateSigner() (ssh.Signer, error) {
	key, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, err
	}
	return ssh.NewSignerFromKey(key)
}

func parsePtyRequest(payload []byte) (pty Pty, ok bool) {
	// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.2
	term, rem, ok := parseString(payload)
	if !ok {
		return
	}
	win, rem, ok := parseWindow(rem)
	if !ok {
		return
	}
	modes, ok := parseTerminalModes(rem)
	if !ok {
		return
	}
	pty = Pty{
		Term:   term,
		Window: win,
		Modes:  modes,
	}
	return
}

func parseX11Request(s []byte) (x11 X11, ok bool) {
	single, s, ok := parseBool(s)
	if !ok {
		return
	}
	protocol, s, ok := parseString(s)
	if !ok {
		return
	}
	data, s, ok := parseString(s)
	if !ok {
		return
	}
	screen, _, ok := parseUint32(s)
	if !ok {
		return
	}
	x11 = X11{
		SingleConnection: single,
		AuthProtocol:     protocol,
		AuthData:         data,
		ScreenNumber:     int(screen),
	}
	return
}

func parseTerminalModes(in []byte) (modes ssh.TerminalModes, ok bool) {
	// See https://datatracker.ietf.org/doc/html/rfc4254#section-8
	_, rem, ok := parseUint32(in)
	if !ok {
		return
	}
	const ttyOpEnd = 0
	for len(rem) > 0 {
		if modes == nil {
			modes = make(ssh.TerminalModes)
		}
		code := uint8(rem[0])
		rem = rem[1:]
		if code == ttyOpEnd || code > 160 {
			break
		}
		var val uint32
		val, rem, ok = parseUint32(rem)
		if !ok {
			return
		}
		modes[code] = val
	}
	ok = true
	return
}

func parseWindow(s []byte) (win Window, rem []byte, ok bool) {
	// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.7
	wCols, rem, ok := parseUint32(s)
	if !ok {
		return
	}
	hRows, rem, ok := parseUint32(rem)
	if !ok {
		return
	}
	wPixels, rem, ok := parseUint32(rem)
	if !ok {
		return
	}
	hPixels, rem, ok := parseUint32(rem)
	if !ok {
		return
	}
	win = Window{
		Width:        int(wCols),
		Height:       int(hRows),
		WidthPixels:  int(wPixels),
		HeightPixels: int(hPixels),
	}
	return
}

func parseString(in []byte) (out string, rem []byte, ok bool) {
	length, rem, ok := parseUint32(in)
	if uint32(len(rem)) < length || !ok { //nolint:gosec // length bounded by packet size
		ok = false
		return
	}
	out, rem = string(rem[:length]), rem[length:]
	ok = true
	return
}

func parseUint32(in []byte) (uint32, []byte, bool) {
	if len(in) < 4 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint32(in), in[4:], true
}

func parseBool(in []byte) (bool, []byte, bool) {
	if len(in) < 1 {
		return false, nil, false
	}
	return uint8(in[0]) == 1, in[1:], true
}