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1 | // Copyright 2011 The Go Authors. All rights reserved. |
2 | // Use of this source code is governed by a BSD-style | |
3 | // license that can be found in the LICENSE file. | |
4 | ||
5 | package ssh | |
6 | ||
7 | import ( | |
8 | "errors" | |
9 | "fmt" | |
10 | "net" | |
11 | "sync" | |
12 | "time" | |
13 | ) | |
14 | ||
15 | // Client implements a traditional SSH client that supports shells, | |
16 | // subprocesses, port forwarding and tunneled dialing. | |
17 | type Client struct { | |
18 | Conn | |
19 | ||
20 | forwards forwardList // forwarded tcpip connections from the remote side | |
21 | mu sync.Mutex | |
22 | channelHandlers map[string]chan NewChannel | |
23 | } | |
24 | ||
25 | // HandleChannelOpen returns a channel on which NewChannel requests | |
26 | // for the given type are sent. If the type already is being handled, | |
27 | // nil is returned. The channel is closed when the connection is closed. | |
28 | func (c *Client) HandleChannelOpen(channelType string) <-chan NewChannel { | |
29 | c.mu.Lock() | |
30 | defer c.mu.Unlock() | |
31 | if c.channelHandlers == nil { | |
32 | // The SSH channel has been closed. | |
33 | c := make(chan NewChannel) | |
34 | close(c) | |
35 | return c | |
36 | } | |
37 | ||
38 | ch := c.channelHandlers[channelType] | |
39 | if ch != nil { | |
40 | return nil | |
41 | } | |
42 | ||
43 | ch = make(chan NewChannel, chanSize) | |
44 | c.channelHandlers[channelType] = ch | |
45 | return ch | |
46 | } | |
47 | ||
48 | // NewClient creates a Client on top of the given connection. | |
49 | func NewClient(c Conn, chans <-chan NewChannel, reqs <-chan *Request) *Client { | |
50 | conn := &Client{ | |
51 | Conn: c, | |
52 | channelHandlers: make(map[string]chan NewChannel, 1), | |
53 | } | |
54 | ||
55 | go conn.handleGlobalRequests(reqs) | |
56 | go conn.handleChannelOpens(chans) | |
57 | go func() { | |
58 | conn.Wait() | |
59 | conn.forwards.closeAll() | |
60 | }() | |
61 | go conn.forwards.handleChannels(conn.HandleChannelOpen("forwarded-tcpip")) | |
62 | return conn | |
63 | } | |
64 | ||
65 | // NewClientConn establishes an authenticated SSH connection using c | |
66 | // as the underlying transport. The Request and NewChannel channels | |
67 | // must be serviced or the connection will hang. | |
68 | func NewClientConn(c net.Conn, addr string, config *ClientConfig) (Conn, <-chan NewChannel, <-chan *Request, error) { | |
69 | fullConf := *config | |
70 | fullConf.SetDefaults() | |
71 | conn := &connection{ | |
72 | sshConn: sshConn{conn: c}, | |
73 | } | |
74 | ||
75 | if err := conn.clientHandshake(addr, &fullConf); err != nil { | |
76 | c.Close() | |
77 | return nil, nil, nil, fmt.Errorf("ssh: handshake failed: %v", err) | |
78 | } | |
79 | conn.mux = newMux(conn.transport) | |
80 | return conn, conn.mux.incomingChannels, conn.mux.incomingRequests, nil | |
81 | } | |
82 | ||
83 | // clientHandshake performs the client side key exchange. See RFC 4253 Section | |
84 | // 7. | |
85 | func (c *connection) clientHandshake(dialAddress string, config *ClientConfig) error { | |
86 | if config.ClientVersion != "" { | |
87 | c.clientVersion = []byte(config.ClientVersion) | |
88 | } else { | |
89 | c.clientVersion = []byte(packageVersion) | |
90 | } | |
91 | var err error | |
92 | c.serverVersion, err = exchangeVersions(c.sshConn.conn, c.clientVersion) | |
93 | if err != nil { | |
94 | return err | |
95 | } | |
96 | ||
97 | c.transport = newClientTransport( | |
98 | newTransport(c.sshConn.conn, config.Rand, true /* is client */), | |
99 | c.clientVersion, c.serverVersion, config, dialAddress, c.sshConn.RemoteAddr()) | |
100 | if err := c.transport.waitSession(); err != nil { | |
101 | return err | |
102 | } | |
103 | ||
104 | c.sessionID = c.transport.getSessionID() | |
105 | return c.clientAuthenticate(config) | |
106 | } | |
107 | ||
108 | // verifyHostKeySignature verifies the host key obtained in the key | |
109 | // exchange. | |
110 | func verifyHostKeySignature(hostKey PublicKey, result *kexResult) error { | |
111 | sig, rest, ok := parseSignatureBody(result.Signature) | |
112 | if len(rest) > 0 || !ok { | |
113 | return errors.New("ssh: signature parse error") | |
114 | } | |
115 | ||
116 | return hostKey.Verify(result.H, sig) | |
117 | } | |
118 | ||
119 | // NewSession opens a new Session for this client. (A session is a remote | |
120 | // execution of a program.) | |
121 | func (c *Client) NewSession() (*Session, error) { | |
122 | ch, in, err := c.OpenChannel("session", nil) | |
123 | if err != nil { | |
124 | return nil, err | |
125 | } | |
126 | return newSession(ch, in) | |
127 | } | |
128 | ||
129 | func (c *Client) handleGlobalRequests(incoming <-chan *Request) { | |
130 | for r := range incoming { | |
131 | // This handles keepalive messages and matches | |
132 | // the behaviour of OpenSSH. | |
133 | r.Reply(false, nil) | |
134 | } | |
135 | } | |
136 | ||
137 | // handleChannelOpens channel open messages from the remote side. | |
138 | func (c *Client) handleChannelOpens(in <-chan NewChannel) { | |
139 | for ch := range in { | |
140 | c.mu.Lock() | |
141 | handler := c.channelHandlers[ch.ChannelType()] | |
142 | c.mu.Unlock() | |
143 | ||
144 | if handler != nil { | |
145 | handler <- ch | |
146 | } else { | |
147 | ch.Reject(UnknownChannelType, fmt.Sprintf("unknown channel type: %v", ch.ChannelType())) | |
148 | } | |
149 | } | |
150 | ||
151 | c.mu.Lock() | |
152 | for _, ch := range c.channelHandlers { | |
153 | close(ch) | |
154 | } | |
155 | c.channelHandlers = nil | |
156 | c.mu.Unlock() | |
157 | } | |
158 | ||
159 | // Dial starts a client connection to the given SSH server. It is a | |
160 | // convenience function that connects to the given network address, | |
161 | // initiates the SSH handshake, and then sets up a Client. For access | |
162 | // to incoming channels and requests, use net.Dial with NewClientConn | |
163 | // instead. | |
164 | func Dial(network, addr string, config *ClientConfig) (*Client, error) { | |
165 | conn, err := net.DialTimeout(network, addr, config.Timeout) | |
166 | if err != nil { | |
167 | return nil, err | |
168 | } | |
169 | c, chans, reqs, err := NewClientConn(conn, addr, config) | |
170 | if err != nil { | |
171 | return nil, err | |
172 | } | |
173 | return NewClient(c, chans, reqs), nil | |
174 | } | |
175 | ||
176 | // A ClientConfig structure is used to configure a Client. It must not be | |
177 | // modified after having been passed to an SSH function. | |
178 | type ClientConfig struct { | |
179 | // Config contains configuration that is shared between clients and | |
180 | // servers. | |
181 | Config | |
182 | ||
183 | // User contains the username to authenticate as. | |
184 | User string | |
185 | ||
186 | // Auth contains possible authentication methods to use with the | |
187 | // server. Only the first instance of a particular RFC 4252 method will | |
188 | // be used during authentication. | |
189 | Auth []AuthMethod | |
190 | ||
191 | // HostKeyCallback, if not nil, is called during the cryptographic | |
192 | // handshake to validate the server's host key. A nil HostKeyCallback | |
193 | // implies that all host keys are accepted. | |
194 | HostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error | |
195 | ||
196 | // ClientVersion contains the version identification string that will | |
197 | // be used for the connection. If empty, a reasonable default is used. | |
198 | ClientVersion string | |
199 | ||
200 | // HostKeyAlgorithms lists the key types that the client will | |
201 | // accept from the server as host key, in order of | |
202 | // preference. If empty, a reasonable default is used. Any | |
203 | // string returned from PublicKey.Type method may be used, or | |
204 | // any of the CertAlgoXxxx and KeyAlgoXxxx constants. | |
205 | HostKeyAlgorithms []string | |
206 | ||
207 | // Timeout is the maximum amount of time for the TCP connection to establish. | |
208 | // | |
209 | // A Timeout of zero means no timeout. | |
210 | Timeout time.Duration | |
211 | } |