tailscale/tempfork/gliderlabs/ssh/server.go
Brad Fitzpatrick 5a44f9f5b5 tempfork: temporarily fork gliderlabs/ssh and x/crypto/ssh
While we rearrange/upstream things.

gliderlabs/ssh is forked into tempfork from our prior fork
at be8b7add40

x/crypto/ssh OTOH is forked at
https://github.com/tailscale/golang-x-crypto because it was gnarlier
to vendor with various internal packages, etc.
Its git history shows where it starts (2c7772ba30643b7a2026cbea938420dce7c6384d).

Updates #3802

Change-Id: I546e5cdf831cfc030a6c42557c0ad2c58766c65f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2022-03-26 21:07:01 -07:00

450 lines
12 KiB
Go

package ssh
import (
"context"
"errors"
"fmt"
"net"
"sync"
"time"
gossh "github.com/tailscale/golang-x-crypto/ssh"
)
// ErrServerClosed is returned by the Server's Serve, ListenAndServe,
// and ListenAndServeTLS methods after a call to Shutdown or Close.
var ErrServerClosed = errors.New("ssh: Server closed")
type SubsystemHandler func(s Session)
var DefaultSubsystemHandlers = map[string]SubsystemHandler{}
type RequestHandler func(ctx Context, srv *Server, req *gossh.Request) (ok bool, payload []byte)
var DefaultRequestHandlers = map[string]RequestHandler{}
type ChannelHandler func(srv *Server, conn *gossh.ServerConn, newChan gossh.NewChannel, ctx Context)
var DefaultChannelHandlers = map[string]ChannelHandler{
"session": DefaultSessionHandler,
}
// Server defines parameters for running an SSH server. The zero value for
// Server is a valid configuration. When both PasswordHandler and
// PublicKeyHandler are nil, no client authentication is performed.
type Server struct {
Addr string // TCP address to listen on, ":22" if empty
Handler Handler // handler to invoke, ssh.DefaultHandler if nil
HostSigners []Signer // private keys for the host key, must have at least one
Version string // server version to be sent before the initial handshake
KeyboardInteractiveHandler KeyboardInteractiveHandler // keyboard-interactive authentication handler
PasswordHandler PasswordHandler // password authentication handler
PublicKeyHandler PublicKeyHandler // public key authentication handler
PtyCallback PtyCallback // callback for allowing PTY sessions, allows all if nil
ConnCallback ConnCallback // optional callback for wrapping net.Conn before handling
LocalPortForwardingCallback LocalPortForwardingCallback // callback for allowing local port forwarding, denies all if nil
ReversePortForwardingCallback ReversePortForwardingCallback // callback for allowing reverse port forwarding, denies all if nil
ServerConfigCallback ServerConfigCallback // callback for configuring detailed SSH options
SessionRequestCallback SessionRequestCallback // callback for allowing or denying SSH sessions
ConnectionFailedCallback ConnectionFailedCallback // callback to report connection failures
IdleTimeout time.Duration // connection timeout when no activity, none if empty
MaxTimeout time.Duration // absolute connection timeout, none if empty
// ChannelHandlers allow overriding the built-in session handlers or provide
// extensions to the protocol, such as tcpip forwarding. By default only the
// "session" handler is enabled.
ChannelHandlers map[string]ChannelHandler
// RequestHandlers allow overriding the server-level request handlers or
// provide extensions to the protocol, such as tcpip forwarding. By default
// no handlers are enabled.
RequestHandlers map[string]RequestHandler
// SubsystemHandlers are handlers which are similar to the usual SSH command
// handlers, but handle named subsystems.
SubsystemHandlers map[string]SubsystemHandler
listenerWg sync.WaitGroup
mu sync.RWMutex
listeners map[net.Listener]struct{}
conns map[*gossh.ServerConn]struct{}
connWg sync.WaitGroup
doneChan chan struct{}
}
func (srv *Server) ensureHostSigner() error {
srv.mu.Lock()
defer srv.mu.Unlock()
if len(srv.HostSigners) == 0 {
signer, err := generateSigner()
if err != nil {
return err
}
srv.HostSigners = append(srv.HostSigners, signer)
}
return nil
}
func (srv *Server) ensureHandlers() {
srv.mu.Lock()
defer srv.mu.Unlock()
if srv.RequestHandlers == nil {
srv.RequestHandlers = map[string]RequestHandler{}
for k, v := range DefaultRequestHandlers {
srv.RequestHandlers[k] = v
}
}
if srv.ChannelHandlers == nil {
srv.ChannelHandlers = map[string]ChannelHandler{}
for k, v := range DefaultChannelHandlers {
srv.ChannelHandlers[k] = v
}
}
if srv.SubsystemHandlers == nil {
srv.SubsystemHandlers = map[string]SubsystemHandler{}
for k, v := range DefaultSubsystemHandlers {
srv.SubsystemHandlers[k] = v
}
}
}
func (srv *Server) config(ctx Context) *gossh.ServerConfig {
srv.mu.RLock()
defer srv.mu.RUnlock()
var config *gossh.ServerConfig
if srv.ServerConfigCallback == nil {
config = &gossh.ServerConfig{}
} else {
config = srv.ServerConfigCallback(ctx)
}
for _, signer := range srv.HostSigners {
config.AddHostKey(signer)
}
if srv.PasswordHandler == nil && srv.PublicKeyHandler == nil && srv.KeyboardInteractiveHandler == nil {
config.NoClientAuth = true
}
if srv.Version != "" {
config.ServerVersion = "SSH-2.0-" + srv.Version
}
if srv.PasswordHandler != nil {
config.PasswordCallback = func(conn gossh.ConnMetadata, password []byte) (*gossh.Permissions, error) {
applyConnMetadata(ctx, conn)
if ok := srv.PasswordHandler(ctx, string(password)); !ok {
return ctx.Permissions().Permissions, fmt.Errorf("permission denied")
}
return ctx.Permissions().Permissions, nil
}
}
if srv.PublicKeyHandler != nil {
config.PublicKeyCallback = func(conn gossh.ConnMetadata, key gossh.PublicKey) (*gossh.Permissions, error) {
applyConnMetadata(ctx, conn)
if ok := srv.PublicKeyHandler(ctx, key); !ok {
return ctx.Permissions().Permissions, fmt.Errorf("permission denied")
}
ctx.SetValue(ContextKeyPublicKey, key)
return ctx.Permissions().Permissions, nil
}
}
if srv.KeyboardInteractiveHandler != nil {
config.KeyboardInteractiveCallback = func(conn gossh.ConnMetadata, challenger gossh.KeyboardInteractiveChallenge) (*gossh.Permissions, error) {
applyConnMetadata(ctx, conn)
if ok := srv.KeyboardInteractiveHandler(ctx, challenger); !ok {
return ctx.Permissions().Permissions, fmt.Errorf("permission denied")
}
return ctx.Permissions().Permissions, nil
}
}
return config
}
// Handle sets the Handler for the server.
func (srv *Server) Handle(fn Handler) {
srv.mu.Lock()
defer srv.mu.Unlock()
srv.Handler = fn
}
// Close immediately closes all active listeners and all active
// connections.
//
// Close returns any error returned from closing the Server's
// underlying Listener(s).
func (srv *Server) Close() error {
srv.mu.Lock()
defer srv.mu.Unlock()
srv.closeDoneChanLocked()
err := srv.closeListenersLocked()
for c := range srv.conns {
c.Close()
delete(srv.conns, c)
}
return err
}
// Shutdown gracefully shuts down the server without interrupting any
// active connections. Shutdown works by first closing all open
// listeners, and then waiting indefinitely for connections to close.
// If the provided context expires before the shutdown is complete,
// then the context's error is returned.
func (srv *Server) Shutdown(ctx context.Context) error {
srv.mu.Lock()
lnerr := srv.closeListenersLocked()
srv.closeDoneChanLocked()
srv.mu.Unlock()
finished := make(chan struct{}, 1)
go func() {
srv.listenerWg.Wait()
srv.connWg.Wait()
finished <- struct{}{}
}()
select {
case <-ctx.Done():
return ctx.Err()
case <-finished:
return lnerr
}
}
// Serve accepts incoming connections on the Listener l, creating a new
// connection goroutine for each. The connection goroutines read requests and then
// calls srv.Handler to handle sessions.
//
// Serve always returns a non-nil error.
func (srv *Server) Serve(l net.Listener) error {
srv.ensureHandlers()
defer l.Close()
if err := srv.ensureHostSigner(); err != nil {
return err
}
if srv.Handler == nil {
srv.Handler = DefaultHandler
}
var tempDelay time.Duration
srv.trackListener(l, true)
defer srv.trackListener(l, false)
for {
conn, e := l.Accept()
if e != nil {
select {
case <-srv.getDoneChan():
return ErrServerClosed
default:
}
if ne, ok := e.(net.Error); ok && ne.Temporary() {
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
time.Sleep(tempDelay)
continue
}
return e
}
go srv.HandleConn(conn)
}
}
func (srv *Server) HandleConn(newConn net.Conn) {
ctx, cancel := newContext(srv)
if srv.ConnCallback != nil {
cbConn := srv.ConnCallback(ctx, newConn)
if cbConn == nil {
newConn.Close()
return
}
newConn = cbConn
}
conn := &serverConn{
Conn: newConn,
idleTimeout: srv.IdleTimeout,
closeCanceler: cancel,
}
if srv.MaxTimeout > 0 {
conn.maxDeadline = time.Now().Add(srv.MaxTimeout)
}
defer conn.Close()
sshConn, chans, reqs, err := gossh.NewServerConn(conn, srv.config(ctx))
if err != nil {
if srv.ConnectionFailedCallback != nil {
srv.ConnectionFailedCallback(conn, err)
}
return
}
srv.trackConn(sshConn, true)
defer srv.trackConn(sshConn, false)
ctx.SetValue(ContextKeyConn, sshConn)
applyConnMetadata(ctx, sshConn)
//go gossh.DiscardRequests(reqs)
go srv.handleRequests(ctx, reqs)
for ch := range chans {
handler := srv.ChannelHandlers[ch.ChannelType()]
if handler == nil {
handler = srv.ChannelHandlers["default"]
}
if handler == nil {
ch.Reject(gossh.UnknownChannelType, "unsupported channel type")
continue
}
go handler(srv, sshConn, ch, ctx)
}
}
func (srv *Server) handleRequests(ctx Context, in <-chan *gossh.Request) {
for req := range in {
handler := srv.RequestHandlers[req.Type]
if handler == nil {
handler = srv.RequestHandlers["default"]
}
if handler == nil {
req.Reply(false, nil)
continue
}
/*reqCtx, cancel := context.WithCancel(ctx)
defer cancel() */
ret, payload := handler(ctx, srv, req)
req.Reply(ret, payload)
}
}
// ListenAndServe listens on the TCP network address srv.Addr and then calls
// Serve to handle incoming connections. If srv.Addr is blank, ":22" is used.
// ListenAndServe always returns a non-nil error.
func (srv *Server) ListenAndServe() error {
addr := srv.Addr
if addr == "" {
addr = ":22"
}
ln, err := net.Listen("tcp", addr)
if err != nil {
return err
}
return srv.Serve(ln)
}
// AddHostKey adds a private key as a host key. If an existing host key exists
// with the same algorithm, it is overwritten. Each server config must have at
// least one host key.
func (srv *Server) AddHostKey(key Signer) {
srv.mu.Lock()
defer srv.mu.Unlock()
// these are later added via AddHostKey on ServerConfig, which performs the
// check for one of every algorithm.
// This check is based on the AddHostKey method from the x/crypto/ssh
// library. This allows us to only keep one active key for each type on a
// server at once. So, if you're dynamically updating keys at runtime, this
// list will not keep growing.
for i, k := range srv.HostSigners {
if k.PublicKey().Type() == key.PublicKey().Type() {
srv.HostSigners[i] = key
return
}
}
srv.HostSigners = append(srv.HostSigners, key)
}
// SetOption runs a functional option against the server.
func (srv *Server) SetOption(option Option) error {
// NOTE: there is a potential race here for any option that doesn't call an
// internal method. We can't actually lock here because if something calls
// (as an example) AddHostKey, it will deadlock.
//srv.mu.Lock()
//defer srv.mu.Unlock()
return option(srv)
}
func (srv *Server) getDoneChan() <-chan struct{} {
srv.mu.Lock()
defer srv.mu.Unlock()
return srv.getDoneChanLocked()
}
func (srv *Server) getDoneChanLocked() chan struct{} {
if srv.doneChan == nil {
srv.doneChan = make(chan struct{})
}
return srv.doneChan
}
func (srv *Server) closeDoneChanLocked() {
ch := srv.getDoneChanLocked()
select {
case <-ch:
// Already closed. Don't close again.
default:
// Safe to close here. We're the only closer, guarded
// by srv.mu.
close(ch)
}
}
func (srv *Server) closeListenersLocked() error {
var err error
for ln := range srv.listeners {
if cerr := ln.Close(); cerr != nil && err == nil {
err = cerr
}
delete(srv.listeners, ln)
}
return err
}
func (srv *Server) trackListener(ln net.Listener, add bool) {
srv.mu.Lock()
defer srv.mu.Unlock()
if srv.listeners == nil {
srv.listeners = make(map[net.Listener]struct{})
}
if add {
// If the *Server is being reused after a previous
// Close or Shutdown, reset its doneChan:
if len(srv.listeners) == 0 && len(srv.conns) == 0 {
srv.doneChan = nil
}
srv.listeners[ln] = struct{}{}
srv.listenerWg.Add(1)
} else {
delete(srv.listeners, ln)
srv.listenerWg.Done()
}
}
func (srv *Server) trackConn(c *gossh.ServerConn, add bool) {
srv.mu.Lock()
defer srv.mu.Unlock()
if srv.conns == nil {
srv.conns = make(map[*gossh.ServerConn]struct{})
}
if add {
srv.conns[c] = struct{}{}
srv.connWg.Add(1)
} else {
delete(srv.conns, c)
srv.connWg.Done()
}
}