461 lines
12 KiB
Go
461 lines
12 KiB
Go
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// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ssh
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import (
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"crypto/rand"
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"errors"
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"fmt"
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"io"
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"log"
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"net"
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"sync"
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)
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// debugHandshake, if set, prints messages sent and received. Key
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// exchange messages are printed as if DH were used, so the debug
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// messages are wrong when using ECDH.
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const debugHandshake = false
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// keyingTransport is a packet based transport that supports key
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// changes. It need not be thread-safe. It should pass through
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// msgNewKeys in both directions.
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type keyingTransport interface {
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packetConn
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// prepareKeyChange sets up a key change. The key change for a
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// direction will be effected if a msgNewKeys message is sent
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// or received.
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prepareKeyChange(*algorithms, *kexResult) error
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}
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// handshakeTransport implements rekeying on top of a keyingTransport
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// and offers a thread-safe writePacket() interface.
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type handshakeTransport struct {
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conn keyingTransport
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config *Config
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serverVersion []byte
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clientVersion []byte
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// hostKeys is non-empty if we are the server. In that case,
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// it contains all host keys that can be used to sign the
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// connection.
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hostKeys []Signer
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// hostKeyAlgorithms is non-empty if we are the client. In that case,
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// we accept these key types from the server as host key.
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hostKeyAlgorithms []string
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// On read error, incoming is closed, and readError is set.
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incoming chan []byte
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readError error
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// data for host key checking
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hostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error
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dialAddress string
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remoteAddr net.Addr
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readSinceKex uint64
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// Protects the writing side of the connection
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mu sync.Mutex
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cond *sync.Cond
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sentInitPacket []byte
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sentInitMsg *kexInitMsg
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writtenSinceKex uint64
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writeError error
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// The session ID or nil if first kex did not complete yet.
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sessionID []byte
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}
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func newHandshakeTransport(conn keyingTransport, config *Config, clientVersion, serverVersion []byte) *handshakeTransport {
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t := &handshakeTransport{
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conn: conn,
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serverVersion: serverVersion,
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clientVersion: clientVersion,
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incoming: make(chan []byte, 16),
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config: config,
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}
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t.cond = sync.NewCond(&t.mu)
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return t
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}
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func newClientTransport(conn keyingTransport, clientVersion, serverVersion []byte, config *ClientConfig, dialAddr string, addr net.Addr) *handshakeTransport {
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t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion)
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t.dialAddress = dialAddr
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t.remoteAddr = addr
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t.hostKeyCallback = config.HostKeyCallback
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if config.HostKeyAlgorithms != nil {
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t.hostKeyAlgorithms = config.HostKeyAlgorithms
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} else {
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t.hostKeyAlgorithms = supportedHostKeyAlgos
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}
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go t.readLoop()
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return t
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}
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func newServerTransport(conn keyingTransport, clientVersion, serverVersion []byte, config *ServerConfig) *handshakeTransport {
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t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion)
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t.hostKeys = config.hostKeys
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go t.readLoop()
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return t
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}
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func (t *handshakeTransport) getSessionID() []byte {
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return t.sessionID
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}
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func (t *handshakeTransport) id() string {
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if len(t.hostKeys) > 0 {
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return "server"
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}
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return "client"
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}
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func (t *handshakeTransport) readPacket() ([]byte, error) {
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p, ok := <-t.incoming
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if !ok {
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return nil, t.readError
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}
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return p, nil
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}
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func (t *handshakeTransport) readLoop() {
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for {
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p, err := t.readOnePacket()
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if err != nil {
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t.readError = err
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close(t.incoming)
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break
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}
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if p[0] == msgIgnore || p[0] == msgDebug {
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continue
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}
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t.incoming <- p
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}
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// If we can't read, declare the writing part dead too.
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t.mu.Lock()
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defer t.mu.Unlock()
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if t.writeError == nil {
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t.writeError = t.readError
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}
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t.cond.Broadcast()
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}
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func (t *handshakeTransport) readOnePacket() ([]byte, error) {
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if t.readSinceKex > t.config.RekeyThreshold {
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if err := t.requestKeyChange(); err != nil {
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return nil, err
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}
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}
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p, err := t.conn.readPacket()
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if err != nil {
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return nil, err
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}
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t.readSinceKex += uint64(len(p))
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if debugHandshake {
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if p[0] == msgChannelData || p[0] == msgChannelExtendedData {
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log.Printf("%s got data (packet %d bytes)", t.id(), len(p))
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} else {
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msg, err := decode(p)
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log.Printf("%s got %T %v (%v)", t.id(), msg, msg, err)
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}
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}
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if p[0] != msgKexInit {
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return p, nil
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}
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t.mu.Lock()
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firstKex := t.sessionID == nil
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err = t.enterKeyExchangeLocked(p)
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if err != nil {
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// drop connection
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t.conn.Close()
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t.writeError = err
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}
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if debugHandshake {
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log.Printf("%s exited key exchange (first %v), err %v", t.id(), firstKex, err)
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}
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// Unblock writers.
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t.sentInitMsg = nil
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t.sentInitPacket = nil
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t.cond.Broadcast()
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t.writtenSinceKex = 0
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t.mu.Unlock()
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if err != nil {
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return nil, err
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}
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t.readSinceKex = 0
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// By default, a key exchange is hidden from higher layers by
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// translating it into msgIgnore.
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successPacket := []byte{msgIgnore}
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if firstKex {
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// sendKexInit() for the first kex waits for
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// msgNewKeys so the authentication process is
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// guaranteed to happen over an encrypted transport.
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successPacket = []byte{msgNewKeys}
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}
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return successPacket, nil
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}
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// keyChangeCategory describes whether a key exchange is the first on a
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// connection, or a subsequent one.
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type keyChangeCategory bool
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const (
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firstKeyExchange keyChangeCategory = true
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subsequentKeyExchange keyChangeCategory = false
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)
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// sendKexInit sends a key change message, and returns the message
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// that was sent. After initiating the key change, all writes will be
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// blocked until the change is done, and a failed key change will
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// close the underlying transport. This function is safe for
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// concurrent use by multiple goroutines.
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func (t *handshakeTransport) sendKexInit(isFirst keyChangeCategory) error {
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var err error
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t.mu.Lock()
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// If this is the initial key change, but we already have a sessionID,
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// then do nothing because the key exchange has already completed
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// asynchronously.
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if !isFirst || t.sessionID == nil {
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_, _, err = t.sendKexInitLocked(isFirst)
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}
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t.mu.Unlock()
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if err != nil {
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return err
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}
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if isFirst {
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if packet, err := t.readPacket(); err != nil {
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return err
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} else if packet[0] != msgNewKeys {
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return unexpectedMessageError(msgNewKeys, packet[0])
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}
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}
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return nil
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}
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func (t *handshakeTransport) requestInitialKeyChange() error {
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return t.sendKexInit(firstKeyExchange)
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}
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func (t *handshakeTransport) requestKeyChange() error {
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return t.sendKexInit(subsequentKeyExchange)
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}
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// sendKexInitLocked sends a key change message. t.mu must be locked
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// while this happens.
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func (t *handshakeTransport) sendKexInitLocked(isFirst keyChangeCategory) (*kexInitMsg, []byte, error) {
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// kexInits may be sent either in response to the other side,
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// or because our side wants to initiate a key change, so we
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// may have already sent a kexInit. In that case, don't send a
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// second kexInit.
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if t.sentInitMsg != nil {
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return t.sentInitMsg, t.sentInitPacket, nil
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}
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msg := &kexInitMsg{
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KexAlgos: t.config.KeyExchanges,
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CiphersClientServer: t.config.Ciphers,
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CiphersServerClient: t.config.Ciphers,
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MACsClientServer: t.config.MACs,
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MACsServerClient: t.config.MACs,
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CompressionClientServer: supportedCompressions,
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CompressionServerClient: supportedCompressions,
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}
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io.ReadFull(rand.Reader, msg.Cookie[:])
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if len(t.hostKeys) > 0 {
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for _, k := range t.hostKeys {
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msg.ServerHostKeyAlgos = append(
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msg.ServerHostKeyAlgos, k.PublicKey().Type())
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}
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} else {
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msg.ServerHostKeyAlgos = t.hostKeyAlgorithms
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}
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packet := Marshal(msg)
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// writePacket destroys the contents, so save a copy.
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packetCopy := make([]byte, len(packet))
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copy(packetCopy, packet)
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if err := t.conn.writePacket(packetCopy); err != nil {
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return nil, nil, err
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}
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t.sentInitMsg = msg
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t.sentInitPacket = packet
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return msg, packet, nil
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}
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func (t *handshakeTransport) writePacket(p []byte) error {
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t.mu.Lock()
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defer t.mu.Unlock()
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if t.writtenSinceKex > t.config.RekeyThreshold {
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t.sendKexInitLocked(subsequentKeyExchange)
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}
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for t.sentInitMsg != nil && t.writeError == nil {
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t.cond.Wait()
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}
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if t.writeError != nil {
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return t.writeError
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}
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t.writtenSinceKex += uint64(len(p))
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switch p[0] {
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case msgKexInit:
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return errors.New("ssh: only handshakeTransport can send kexInit")
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case msgNewKeys:
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return errors.New("ssh: only handshakeTransport can send newKeys")
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default:
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return t.conn.writePacket(p)
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}
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}
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func (t *handshakeTransport) Close() error {
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return t.conn.Close()
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}
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// enterKeyExchange runs the key exchange. t.mu must be held while running this.
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func (t *handshakeTransport) enterKeyExchangeLocked(otherInitPacket []byte) error {
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if debugHandshake {
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log.Printf("%s entered key exchange", t.id())
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}
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myInit, myInitPacket, err := t.sendKexInitLocked(subsequentKeyExchange)
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if err != nil {
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return err
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}
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otherInit := &kexInitMsg{}
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if err := Unmarshal(otherInitPacket, otherInit); err != nil {
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return err
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}
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magics := handshakeMagics{
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clientVersion: t.clientVersion,
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serverVersion: t.serverVersion,
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clientKexInit: otherInitPacket,
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serverKexInit: myInitPacket,
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}
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clientInit := otherInit
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serverInit := myInit
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if len(t.hostKeys) == 0 {
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clientInit = myInit
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serverInit = otherInit
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magics.clientKexInit = myInitPacket
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magics.serverKexInit = otherInitPacket
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}
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algs, err := findAgreedAlgorithms(clientInit, serverInit)
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if err != nil {
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return err
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}
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// We don't send FirstKexFollows, but we handle receiving it.
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//
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// RFC 4253 section 7 defines the kex and the agreement method for
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// first_kex_packet_follows. It states that the guessed packet
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// should be ignored if the "kex algorithm and/or the host
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// key algorithm is guessed wrong (server and client have
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// different preferred algorithm), or if any of the other
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// algorithms cannot be agreed upon". The other algorithms have
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// already been checked above so the kex algorithm and host key
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// algorithm are checked here.
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if otherInit.FirstKexFollows && (clientInit.KexAlgos[0] != serverInit.KexAlgos[0] || clientInit.ServerHostKeyAlgos[0] != serverInit.ServerHostKeyAlgos[0]) {
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// other side sent a kex message for the wrong algorithm,
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// which we have to ignore.
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if _, err := t.conn.readPacket(); err != nil {
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return err
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}
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}
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kex, ok := kexAlgoMap[algs.kex]
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if !ok {
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return fmt.Errorf("ssh: unexpected key exchange algorithm %v", algs.kex)
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}
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|
|
||
|
|
var result *kexResult
|
||
|
|
if len(t.hostKeys) > 0 {
|
||
|
|
result, err = t.server(kex, algs, &magics)
|
||
|
|
} else {
|
||
|
|
result, err = t.client(kex, algs, &magics)
|
||
|
|
}
|
||
|
|
|
||
|
|
if err != nil {
|
||
|
|
return err
|
||
|
|
}
|
||
|
|
|
||
|
|
if t.sessionID == nil {
|
||
|
|
t.sessionID = result.H
|
||
|
|
}
|
||
|
|
result.SessionID = t.sessionID
|
||
|
|
|
||
|
|
t.conn.prepareKeyChange(algs, result)
|
||
|
|
if err = t.conn.writePacket([]byte{msgNewKeys}); err != nil {
|
||
|
|
return err
|
||
|
|
}
|
||
|
|
if packet, err := t.conn.readPacket(); err != nil {
|
||
|
|
return err
|
||
|
|
} else if packet[0] != msgNewKeys {
|
||
|
|
return unexpectedMessageError(msgNewKeys, packet[0])
|
||
|
|
}
|
||
|
|
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
func (t *handshakeTransport) server(kex kexAlgorithm, algs *algorithms, magics *handshakeMagics) (*kexResult, error) {
|
||
|
|
var hostKey Signer
|
||
|
|
for _, k := range t.hostKeys {
|
||
|
|
if algs.hostKey == k.PublicKey().Type() {
|
||
|
|
hostKey = k
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
r, err := kex.Server(t.conn, t.config.Rand, magics, hostKey)
|
||
|
|
return r, err
|
||
|
|
}
|
||
|
|
|
||
|
|
func (t *handshakeTransport) client(kex kexAlgorithm, algs *algorithms, magics *handshakeMagics) (*kexResult, error) {
|
||
|
|
result, err := kex.Client(t.conn, t.config.Rand, magics)
|
||
|
|
if err != nil {
|
||
|
|
return nil, err
|
||
|
|
}
|
||
|
|
|
||
|
|
hostKey, err := ParsePublicKey(result.HostKey)
|
||
|
|
if err != nil {
|
||
|
|
return nil, err
|
||
|
|
}
|
||
|
|
|
||
|
|
if err := verifyHostKeySignature(hostKey, result); err != nil {
|
||
|
|
return nil, err
|
||
|
|
}
|
||
|
|
|
||
|
|
if t.hostKeyCallback != nil {
|
||
|
|
err = t.hostKeyCallback(t.dialAddress, t.remoteAddr, hostKey)
|
||
|
|
if err != nil {
|
||
|
|
return nil, err
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return result, nil
|
||
|
|
}
|