mirror of
https://github.com/go-gitea/gitea.git
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647 lines
16 KiB
Go
647 lines
16 KiB
Go
// 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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// chanSize sets the amount of buffering SSH connections. This is
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// primarily for testing: setting chanSize=0 uncovers deadlocks more
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// quickly.
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const chanSize = 16
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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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mu sync.Mutex
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writeError error
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sentInitPacket []byte
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sentInitMsg *kexInitMsg
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pendingPackets [][]byte // Used when a key exchange is in progress.
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// If the read loop wants to schedule a kex, it pings this
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// channel, and the write loop will send out a kex
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// message.
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requestKex chan struct{}
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// If the other side requests or confirms a kex, its kexInit
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// packet is sent here for the write loop to find it.
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startKex chan *pendingKex
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// data for host key checking
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hostKeyCallback HostKeyCallback
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dialAddress string
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remoteAddr net.Addr
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// bannerCallback is non-empty if we are the client and it has been set in
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// ClientConfig. In that case it is called during the user authentication
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// dance to handle a custom server's message.
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bannerCallback BannerCallback
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// Algorithms agreed in the last key exchange.
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algorithms *algorithms
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readPacketsLeft uint32
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readBytesLeft int64
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writePacketsLeft uint32
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writeBytesLeft int64
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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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type pendingKex struct {
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otherInit []byte
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done chan error
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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, chanSize),
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requestKex: make(chan struct{}, 1),
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startKex: make(chan *pendingKex, 1),
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config: config,
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}
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t.resetReadThresholds()
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t.resetWriteThresholds()
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// We always start with a mandatory key exchange.
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t.requestKex <- struct{}{}
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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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t.bannerCallback = config.BannerCallback
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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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go t.kexLoop()
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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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go t.kexLoop()
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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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// waitSession waits for the session to be established. This should be
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// the first thing to call after instantiating handshakeTransport.
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func (t *handshakeTransport) waitSession() error {
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p, err := t.readPacket()
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if err != nil {
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return err
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}
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if p[0] != msgNewKeys {
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return fmt.Errorf("ssh: first packet should be msgNewKeys")
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}
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return nil
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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) printPacket(p []byte, write bool) {
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action := "got"
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if write {
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action = "sent"
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}
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if p[0] == msgChannelData || p[0] == msgChannelExtendedData {
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log.Printf("%s %s data (packet %d bytes)", t.id(), action, len(p))
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} else {
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msg, err := decode(p)
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log.Printf("%s %s %T %v (%v)", t.id(), action, msg, msg, err)
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}
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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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first := true
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for {
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p, err := t.readOnePacket(first)
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first = false
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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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// Stop writers too.
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t.recordWriteError(t.readError)
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// Unblock the writer should it wait for this.
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close(t.startKex)
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// Don't close t.requestKex; it's also written to from writePacket.
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}
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func (t *handshakeTransport) pushPacket(p []byte) error {
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if debugHandshake {
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t.printPacket(p, true)
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}
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return t.conn.writePacket(p)
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}
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func (t *handshakeTransport) getWriteError() error {
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t.mu.Lock()
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defer t.mu.Unlock()
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return t.writeError
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}
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func (t *handshakeTransport) recordWriteError(err error) {
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t.mu.Lock()
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defer t.mu.Unlock()
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if t.writeError == nil && err != nil {
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t.writeError = err
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}
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}
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func (t *handshakeTransport) requestKeyExchange() {
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select {
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case t.requestKex <- struct{}{}:
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default:
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// something already requested a kex, so do nothing.
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}
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}
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func (t *handshakeTransport) resetWriteThresholds() {
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t.writePacketsLeft = packetRekeyThreshold
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if t.config.RekeyThreshold > 0 {
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t.writeBytesLeft = int64(t.config.RekeyThreshold)
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} else if t.algorithms != nil {
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t.writeBytesLeft = t.algorithms.w.rekeyBytes()
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} else {
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t.writeBytesLeft = 1 << 30
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}
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}
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func (t *handshakeTransport) kexLoop() {
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write:
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for t.getWriteError() == nil {
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var request *pendingKex
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var sent bool
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for request == nil || !sent {
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var ok bool
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select {
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case request, ok = <-t.startKex:
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if !ok {
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break write
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}
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case <-t.requestKex:
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break
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}
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if !sent {
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if err := t.sendKexInit(); err != nil {
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t.recordWriteError(err)
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break
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}
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sent = true
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}
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}
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if err := t.getWriteError(); err != nil {
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if request != nil {
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request.done <- err
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}
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break
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}
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// We're not servicing t.requestKex, but that is OK:
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// we never block on sending to t.requestKex.
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// We're not servicing t.startKex, but the remote end
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// has just sent us a kexInitMsg, so it can't send
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// another key change request, until we close the done
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// channel on the pendingKex request.
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err := t.enterKeyExchange(request.otherInit)
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t.mu.Lock()
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t.writeError = err
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t.sentInitPacket = nil
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t.sentInitMsg = nil
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t.resetWriteThresholds()
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// we have completed the key exchange. Since the
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// reader is still blocked, it is safe to clear out
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// the requestKex channel. This avoids the situation
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// where: 1) we consumed our own request for the
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// initial kex, and 2) the kex from the remote side
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// caused another send on the requestKex channel,
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clear:
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for {
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select {
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case <-t.requestKex:
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//
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default:
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break clear
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}
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}
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request.done <- t.writeError
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// kex finished. Push packets that we received while
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// the kex was in progress. Don't look at t.startKex
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// and don't increment writtenSinceKex: if we trigger
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// another kex while we are still busy with the last
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// one, things will become very confusing.
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for _, p := range t.pendingPackets {
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t.writeError = t.pushPacket(p)
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if t.writeError != nil {
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break
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}
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}
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t.pendingPackets = t.pendingPackets[:0]
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t.mu.Unlock()
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}
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// drain startKex channel. We don't service t.requestKex
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// because nobody does blocking sends there.
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go func() {
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for init := range t.startKex {
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init.done <- t.writeError
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}
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}()
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// Unblock reader.
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t.conn.Close()
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}
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// The protocol uses uint32 for packet counters, so we can't let them
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// reach 1<<32. We will actually read and write more packets than
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// this, though: the other side may send more packets, and after we
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// hit this limit on writing we will send a few more packets for the
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// key exchange itself.
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const packetRekeyThreshold = (1 << 31)
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func (t *handshakeTransport) resetReadThresholds() {
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t.readPacketsLeft = packetRekeyThreshold
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if t.config.RekeyThreshold > 0 {
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t.readBytesLeft = int64(t.config.RekeyThreshold)
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} else if t.algorithms != nil {
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t.readBytesLeft = t.algorithms.r.rekeyBytes()
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} else {
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t.readBytesLeft = 1 << 30
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}
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}
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func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) {
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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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if t.readPacketsLeft > 0 {
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t.readPacketsLeft--
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} else {
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t.requestKeyExchange()
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}
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if t.readBytesLeft > 0 {
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t.readBytesLeft -= int64(len(p))
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} else {
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t.requestKeyExchange()
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}
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if debugHandshake {
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t.printPacket(p, false)
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}
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if first && p[0] != msgKexInit {
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return nil, fmt.Errorf("ssh: first packet should be msgKexInit")
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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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firstKex := t.sessionID == nil
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kex := pendingKex{
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done: make(chan error, 1),
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otherInit: p,
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}
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t.startKex <- &kex
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err = <-kex.done
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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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if err != nil {
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return nil, err
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}
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t.resetReadThresholds()
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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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// sendKexInit sends a key change message.
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func (t *handshakeTransport) sendKexInit() error {
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t.mu.Lock()
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defer t.mu.Unlock()
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if t.sentInitMsg != nil {
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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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return 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.pushPacket(packetCopy); err != nil {
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return err
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}
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t.sentInitMsg = msg
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t.sentInitPacket = packet
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return nil
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}
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func (t *handshakeTransport) writePacket(p []byte) error {
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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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}
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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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return t.writeError
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}
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if t.sentInitMsg != nil {
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// Copy the packet so the writer can reuse the buffer.
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cp := make([]byte, len(p))
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copy(cp, p)
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t.pendingPackets = append(t.pendingPackets, cp)
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return nil
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}
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if t.writeBytesLeft > 0 {
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t.writeBytesLeft -= int64(len(p))
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} else {
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t.requestKeyExchange()
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}
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if t.writePacketsLeft > 0 {
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t.writePacketsLeft--
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} else {
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t.requestKeyExchange()
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}
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if err := t.pushPacket(p); err != nil {
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t.writeError = err
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}
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return nil
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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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func (t *handshakeTransport) enterKeyExchange(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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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: t.sentInitPacket,
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}
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clientInit := otherInit
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serverInit := t.sentInitMsg
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if len(t.hostKeys) == 0 {
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clientInit, serverInit = serverInit, clientInit
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magics.clientKexInit = t.sentInitPacket
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magics.serverKexInit = otherInitPacket
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}
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var err error
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t.algorithms, 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.
|
|
if _, err := t.conn.readPacket(); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
kex, ok := kexAlgoMap[t.algorithms.kex]
|
|
if !ok {
|
|
return fmt.Errorf("ssh: unexpected key exchange algorithm %v", t.algorithms.kex)
|
|
}
|
|
|
|
var result *kexResult
|
|
if len(t.hostKeys) > 0 {
|
|
result, err = t.server(kex, t.algorithms, &magics)
|
|
} else {
|
|
result, err = t.client(kex, t.algorithms, &magics)
|
|
}
|
|
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
if t.sessionID == nil {
|
|
t.sessionID = result.H
|
|
}
|
|
result.SessionID = t.sessionID
|
|
|
|
if err := t.conn.prepareKeyChange(t.algorithms, result); err != nil {
|
|
return err
|
|
}
|
|
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
|
|
}
|
|
|
|
err = t.hostKeyCallback(t.dialAddress, t.remoteAddr, hostKey)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
return result, nil
|
|
}
|