wgengine/netstack: add an SSH server experiment

Disabled by default.

To use, run tailscaled with:

    TS_SSH_ALLOW_LOGIN=you@bar.com

And enable with:

    $ TAILSCALE_USE_WIP_CODE=true tailscale up --ssh=true

Then ssh [any-user]@[your-tailscale-ip] for a root bash shell.
(both the "root" and "bash" part are temporary)

Updates #3802

Change-Id: I268f8c3c95c8eed5f3231d712a5dc89615a406f0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/up.go

@@ -24,6 +24,7 @@ import (
 	qrcode "github.com/skip2/go-qrcode"
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/safesocket"
@@ -81,6 +82,8 @@ func acceptRouteDefault(goos string) bool {
 
 var upFlagSet = newUpFlagSet(effectiveGOOS(), &upArgs)
 
+func inTest() bool { return flag.Lookup("test.v") != nil }
+
 func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
 	upf := newFlagSet("up")
 
@@ -96,6 +99,9 @@ func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
 	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP or base name) for internet traffic, or empty string to not use an exit node")
 	upf.BoolVar(&upArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
 	upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
+	if envknob.UseWIPCode() || inTest() {
+		upf.BoolVar(&upArgs.runSSH, "ssh", false, "run an SSH server, permitting access per tailnet admin's declared policy")
+	}
 	upf.StringVar(&upArgs.advertiseTags, "advertise-tags", "", "comma-separated ACL tags to request; each must start with \"tag:\" (e.g. \"tag:eng,tag:montreal,tag:ssh\")")
 	upf.StringVar(&upArgs.authKeyOrFile, "authkey", "", `node authorization key; if it begins with "file:", then it's a path to a file containing the authkey`)
 	upf.StringVar(&upArgs.hostname, "hostname", "", "hostname to use instead of the one provided by the OS")
@@ -131,6 +137,7 @@ type upArgsT struct {
 	exitNodeIP             string
 	exitNodeAllowLANAccess bool
 	shieldsUp              bool
+	runSSH                 bool
 	forceReauth            bool
 	forceDaemon            bool
 	advertiseRoutes        string
@@ -352,6 +359,7 @@ func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goo
 	prefs.CorpDNS = upArgs.acceptDNS
 	prefs.AllowSingleHosts = upArgs.singleRoutes
 	prefs.ShieldsUp = upArgs.shieldsUp
+	prefs.RunSSH = upArgs.runSSH
 	prefs.AdvertiseRoutes = routes
 	prefs.AdvertiseTags = tags
 	prefs.Hostname = upArgs.hostname
@@ -712,6 +720,7 @@ func init() {
 	addPrefFlagMapping("exit-node-allow-lan-access", "ExitNodeAllowLANAccess")
 	addPrefFlagMapping("unattended", "ForceDaemon")
 	addPrefFlagMapping("operator", "OperatorUser")
+	addPrefFlagMapping("ssh", "RunSSH")
 }
 
 func addPrefFlagMapping(flagName string, prefNames ...string) {
@@ -902,6 +911,8 @@ func prefsToFlags(env upCheckEnv, prefs *ipn.Prefs) (flagVal map[string]interfac
 		switch f.Name {
 		default:
 			panic(fmt.Sprintf("unhandled flag %q", f.Name))
+		case "ssh":
+			set(prefs.RunSSH)
 		case "login-server":
 			set(prefs.ControlURL)
 		case "accept-routes":

cmd/tailscaled/depaware.txt

@@ -3,6 +3,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    W 💣 github.com/alexbrainman/sspi                                 from github.com/alexbrainman/sspi/internal/common+
    W    github.com/alexbrainman/sspi/internal/common                 from github.com/alexbrainman/sspi/negotiate
    W 💣 github.com/alexbrainman/sspi/negotiate                       from tailscale.com/net/tshttpproxy
+   L    github.com/anmitsu/go-shlex                                  from github.com/gliderlabs/ssh
    L    github.com/aws/aws-sdk-go-v2                                 from github.com/aws/aws-sdk-go-v2/internal/ini
    L    github.com/aws/aws-sdk-go-v2/aws                             from github.com/aws/aws-sdk-go-v2/aws/middleware+
    L    github.com/aws/aws-sdk-go-v2/aws/arn                         from tailscale.com/ipn/store/aws
@@ -60,6 +61,8 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    L    github.com/aws/smithy-go/transport/http/internal/io          from github.com/aws/smithy-go/transport/http
    L    github.com/aws/smithy-go/waiter                              from github.com/aws/aws-sdk-go-v2/service/ssm
    L    github.com/coreos/go-iptables/iptables                       from tailscale.com/wgengine/router
+   L 💣 github.com/creack/pty                                        from tailscale.com/wgengine/netstack
+   L    github.com/gliderlabs/ssh                                    from tailscale.com/wgengine/netstack
    W 💣 github.com/go-ole/go-ole                                     from github.com/go-ole/go-ole/oleutil+
    W 💣 github.com/go-ole/go-ole/oleutil                             from tailscale.com/wgengine/winnet
    L 💣 github.com/godbus/dbus/v5                                    from tailscale.com/net/dns
@@ -256,7 +259,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/filter                                from tailscale.com/control/controlclient+
         tailscale.com/wgengine/magicsock                             from tailscale.com/wgengine+
         tailscale.com/wgengine/monitor                               from tailscale.com/cmd/tailscaled+
-        tailscale.com/wgengine/netstack                              from tailscale.com/cmd/tailscaled
+     💣 tailscale.com/wgengine/netstack                              from tailscale.com/cmd/tailscaled
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
         tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
@@ -265,16 +268,19 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/acme                                     from tailscale.com/ipn/localapi
         golang.org/x/crypto/blake2b                                  from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/blake2s                                  from golang.zx2c4.com/wireguard/device
-        golang.org/x/crypto/chacha20                                 from golang.org/x/crypto/chacha20poly1305
+   L    golang.org/x/crypto/blowfish                                 from golang.org/x/crypto/ssh/internal/bcrypt_pbkdf
+        golang.org/x/crypto/chacha20                                 from golang.org/x/crypto/chacha20poly1305+
         golang.org/x/crypto/chacha20poly1305                         from crypto/tls+
         golang.org/x/crypto/cryptobyte                               from crypto/ecdsa+
         golang.org/x/crypto/cryptobyte/asn1                          from crypto/ecdsa+
         golang.org/x/crypto/curve25519                               from crypto/tls+
+   L    golang.org/x/crypto/ed25519                                  from golang.org/x/crypto/ssh
         golang.org/x/crypto/hkdf                                     from crypto/tls
         golang.org/x/crypto/nacl/box                                 from tailscale.com/types/key
         golang.org/x/crypto/nacl/secretbox                           from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/poly1305                                 from golang.org/x/crypto/chacha20poly1305+
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
+   L    golang.org/x/crypto/ssh                                      from github.com/gliderlabs/ssh+
         golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from net+
         golang.org/x/net/http/httpguts                               from net/http+
@@ -312,14 +318,14 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         crypto/aes                                                   from crypto/ecdsa+
         crypto/cipher                                                from crypto/aes+
         crypto/des                                                   from crypto/tls+
-        crypto/dsa                                                   from crypto/x509
+        crypto/dsa                                                   from crypto/x509+
         crypto/ecdsa                                                 from crypto/tls+
         crypto/ed25519                                               from crypto/tls+
         crypto/elliptic                                              from crypto/ecdsa+
         crypto/hmac                                                  from crypto/tls+
         crypto/md5                                                   from crypto/tls+
         crypto/rand                                                  from crypto/ed25519+
-        crypto/rc4                                                   from crypto/tls
+        crypto/rc4                                                   from crypto/tls+
         crypto/rsa                                                   from crypto/tls+
         crypto/sha1                                                  from crypto/tls+
         crypto/sha256                                                from crypto/tls+

cmd/tailscaled/tailscaled.go

@@ -329,9 +329,6 @@ func run() error {
 	}
 	ns.ProcessLocalIPs = useNetstack
 	ns.ProcessSubnets = useNetstack || wrapNetstack
-	if err := ns.Start(); err != nil {
-		return fmt.Errorf("failed to start netstack: %w", err)
-	}
 
 	if useNetstack {
 		dialer.UseNetstackForIP = func(ip netaddr.IP) bool {
@@ -342,7 +339,6 @@ func run() error {
 			return ns.DialContextTCP(ctx, dst)
 		}
 	}
-
 	if socksListener != nil || httpProxyListener != nil {
 		if httpProxyListener != nil {
 			hs := &http.Server{Handler: httpProxyHandler(dialer.UserDial)}
@@ -392,6 +388,10 @@ func run() error {
 	if err != nil {
 		return fmt.Errorf("ipnserver.New: %w", err)
 	}
+	ns.SetLocalBackend(srv.LocalBackend())
+	if err := ns.Start(); err != nil {
+		log.Fatalf("failed to start netstack: %v", err)
+	}
 
 	if debugMux != nil {
 		debugMux.HandleFunc("/debug/ipn", srv.ServeHTMLStatus)

envknob/envknob.go

@@ -100,3 +100,7 @@ func LookupInt(envVar string) (v int, ok bool) {
 	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
 	panic("unreachable")
 }
+
+// UseWIPCode is whether TAILSCALE_USE_WIP_CODE is set to permit use
+// of Work-In-Progress code.
+func UseWIPCode() bool { return Bool("TAILSCALE_USE_WIP_CODE") }

ipn/ipnlocal/local.go

@@ -39,6 +39,7 @@ import (
 	"tailscale.com/net/tsdial"
 	"tailscale.com/paths"
 	"tailscale.com/portlist"
+	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/dnstype"
 	"tailscale.com/types/empty"
@@ -100,6 +101,7 @@ type LocalBackend struct {
 	serverURL             string           // tailcontrol URL
 	newDecompressor       func() (controlclient.Decompressor, error)
 	varRoot               string // or empty if SetVarRoot never called
+	sshAtomicBool         syncs.AtomicBool
 
 	filterHash deephash.Sum
 
@@ -1536,6 +1538,9 @@ func (b *LocalBackend) loadStateLocked(key ipn.StateKey, prefs *ipn.Prefs) (err
 	}
 
 	b.logf("backend prefs for %q: %s", key, b.prefs.Pretty())
+
+	b.sshAtomicBool.Set(b.prefs != nil && b.prefs.RunSSH)
+
 	return nil
 }
 
@@ -1709,6 +1714,8 @@ func (b *LocalBackend) setPrefsLockedOnEntry(caller string, newp *ipn.Prefs) {
 	netMap := b.netMap
 	stateKey := b.stateKey
 
+	b.sshAtomicBool.Set(newp.RunSSH)
+
 	oldp := b.prefs
 	newp.Persist = oldp.Persist // caller isn't allowed to override this
 	b.prefs = newp
@@ -2618,8 +2625,11 @@ func (b *LocalBackend) ResetForClientDisconnect() {
 	b.authURL = ""
 	b.authURLSticky = ""
 	b.activeLogin = ""
+	b.sshAtomicBool.Set(false)
 }
 
+func (b *LocalBackend) ShouldRunSSH() bool { return b.sshAtomicBool.Get() }
+
 // Logout tells the controlclient that we want to log out, and
 // transitions the local engine to the logged-out state without
 // waiting for controlclient to be in that state.

ipn/prefs.go

@@ -98,6 +98,11 @@ type Prefs struct {
 	// DNS configuration, if it exists.
 	CorpDNS bool
 
+	// RunSSH bool is whether this node should run an SSH
+	// server, permitting access to peers according to the
+	// policies as configured by the Tailnet's admin(s).
+	RunSSH bool
+
 	// WantRunning indicates whether networking should be active on
 	// this node.
 	WantRunning bool
@@ -193,6 +198,7 @@ type MaskedPrefs struct {
 	ExitNodeIPSet             bool `json:",omitempty"`
 	ExitNodeAllowLANAccessSet bool `json:",omitempty"`
 	CorpDNSSet                bool `json:",omitempty"`
+	RunSSHSet                 bool `json:",omitempty"`
 	WantRunningSet            bool `json:",omitempty"`
 	LoggedOutSet              bool `json:",omitempty"`
 	ShieldsUpSet              bool `json:",omitempty"`
@@ -277,6 +283,9 @@ func (p *Prefs) pretty(goos string) string {
 		sb.WriteString("mesh=false ")
 	}
 	fmt.Fprintf(&sb, "dns=%v want=%v ", p.CorpDNS, p.WantRunning)
+	if p.RunSSH {
+		sb.WriteString("ssh=true ")
+	}
 	if p.LoggedOut {
 		sb.WriteString("loggedout=true ")
 	}
@@ -348,6 +357,7 @@ func (p *Prefs) Equals(p2 *Prefs) bool {
 		p.ExitNodeIP == p2.ExitNodeIP &&
 		p.ExitNodeAllowLANAccess == p2.ExitNodeAllowLANAccess &&
 		p.CorpDNS == p2.CorpDNS &&
+		p.RunSSH == p2.RunSSH &&
 		p.WantRunning == p2.WantRunning &&
 		p.LoggedOut == p2.LoggedOut &&
 		p.NotepadURLs == p2.NotepadURLs &&

ipn/prefs_test.go

@@ -42,6 +42,7 @@ func TestPrefsEqual(t *testing.T) {
 		"ExitNodeIP",
 		"ExitNodeAllowLANAccess",
 		"CorpDNS",
+		"RunSSH",
 		"WantRunning",
 		"LoggedOut",
 		"ShieldsUp",

tsnet/tsnet.go

@@ -16,14 +16,14 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
 
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale"
 	"tailscale.com/control/controlclient"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/localapi"
@@ -89,7 +89,7 @@ func (s *Server) Start() error {
 }
 
 func (s *Server) start() error {
-	if v, _ := strconv.ParseBool(os.Getenv("TAILSCALE_USE_WIP_CODE")); !v {
+	if !envknob.UseWIPCode() {
 		return errors.New("code disabled without environment variable TAILSCALE_USE_WIP_CODE set true")
 	}