xsd: Added -aK,-aC,-aH to control accepted client proposals

xs/xs.go

@@ -34,9 +34,9 @@ import (
 	_ "net/http/pprof"
 
 	xs "blitter.com/go/xs"
-	"blitter.com/go/xs/xsnet"
 	"blitter.com/go/xs/logger"
 	"blitter.com/go/xs/spinsult"
+	"blitter.com/go/xs/xsnet"
 	isatty "github.com/mattn/go-isatty"
 )
 
@@ -831,13 +831,15 @@ func main() {
 		fmt.Println(err)
 		exitWithStatus(3)
 	}
-	defer conn.Close() // nolint: errcheck
-	// From this point on, conn is a secure encrypted channel
 
 	// Set stdin in raw mode if it's an interactive session
 	// TODO: send flag to server side indicating this
 	//  affects shell command used
 	var oldState *xs.State
+	defer conn.Close() // nolint: errcheck
+
+	// From this point on, conn is a secure encrypted channel
+
 	if shellMode {
 		if isatty.IsTerminal(os.Stdin.Fd()) {
 			oldState, err = xs.MakeRaw(int(os.Stdin.Fd()))
@@ -869,7 +871,11 @@ func main() {
 	rec := xs.NewSession(op, []byte(uname), []byte(remoteHost), []byte(os.Getenv("TERM")), []byte(cmdStr), []byte(authCookie), 0)
 	sendErr := sendSessionParams(&conn, rec)
 	if sendErr != nil {
-		log.Fatal(sendErr)
+		_ = xs.Restore(int(os.Stdin.Fd()), oldState) // nolint: errcheck,gosec
+		rec.SetStatus(254)
+		fmt.Fprintln(os.Stderr, "Error: server rejected secure proposal params") // nolint: errcheck
+		exitWithStatus(int(rec.Status()))
+		//log.Fatal(sendErr)
 	}
 
 	//Security scrub
@@ -931,6 +937,7 @@ func main() {
 
 	if oldState != nil {
 		_ = xs.Restore(int(os.Stdin.Fd()), oldState) // nolint: gosec
+		oldState = nil
 	}
 
 	exitWithStatus(int(rec.Status()))

xsd/xsd.go

@@ -23,14 +23,15 @@ import (
 	"os/signal"
 	"os/user"
 	"path"
+	"strings"
 	"sync"
 	"syscall"
 	"unsafe"
 
 	"blitter.com/go/goutmp"
 	xs "blitter.com/go/xs"
-	"blitter.com/go/xs/xsnet"
 	"blitter.com/go/xs/logger"
+	"blitter.com/go/xs/xsnet"
 	"github.com/kr/pty"
 )
 
@@ -429,9 +430,73 @@ func GenAuthToken(who string, connhost string) string {
 	return fmt.Sprintf("%s:%s", tokenA, hex.EncodeToString(tokenB))
 }
 
-// Demo of a simple server that listens and spawns goroutines for each
-// connecting client. Note this code is identical to standard tcp
-// server code, save for declaring 'xsnet' rather than 'net'
+var (
+	aKEXAlgs    allowedKEXAlgs
+	aCipherAlgs allowedCipherAlgs
+	aHMACAlgs   allowedHMACAlgs
+)
+
+type allowedKEXAlgs []string    // TODO
+type allowedCipherAlgs []string // TODO
+type allowedHMACAlgs []string   // TODO
+
+func (a allowedKEXAlgs) allowed(k xsnet.KEXAlg) bool {
+	for i := 0; i < len(a); i++ {
+		if a[i] == "KEX_all" || a[i] == k.String() {
+			return true
+		}
+	}
+	return false
+}
+
+func (a *allowedKEXAlgs) String() string {
+	return fmt.Sprintf("allowedKEXAlgs: %v", *a)
+}
+
+func (a *allowedKEXAlgs) Set(value string) error {
+	*a = append(*a, strings.TrimSpace(value))
+	return nil
+}
+
+func (a allowedCipherAlgs) allowed(c xsnet.CSCipherAlg) bool {
+	for i := 0; i < len(a); i++ {
+		if a[i] == "C_all" || a[i] == c.String() {
+			return true
+		}
+	}
+	return false
+}
+
+func (a *allowedCipherAlgs) String() string {
+	return fmt.Sprintf("allowedCipherAlgs: %v", *a)
+}
+
+func (a *allowedCipherAlgs) Set(value string) error {
+	*a = append(*a, strings.TrimSpace(value))
+	return nil
+}
+
+func (a allowedHMACAlgs) allowed(h xsnet.CSHmacAlg) bool {
+	for i := 0; i < len(a); i++ {
+		if a[i] == "H_all" || a[i] == h.String() {
+			return true
+		}
+	}
+	return false
+}
+
+func (a *allowedHMACAlgs) String() string {
+	return fmt.Sprintf("allowedHMACAlgs: %v", *a)
+}
+
+func (a *allowedHMACAlgs) Set(value string) error {
+	*a = append(*a, strings.TrimSpace(value))
+	return nil
+}
+
+// Main server that listens and spawns goroutines for each
+// connecting client. Note this code is mostly identical to standard
+// tcp server code, save for declaring 'xsnet' rather than 'net'
 // Listener and Conns. The KEx and encrypt/decrypt is done within the type.
 // Compare to 'serverp.go' in this directory to see the equivalence.
 // TODO: reduce gocyclo
@@ -453,6 +518,11 @@ func main() {
 	flag.UintVar(&chaffFreqMax, "F", 5000, "chaff pkt freq max (msecs)")
 	flag.UintVar(&chaffBytesMax, "B", 64, "chaff pkt size max (bytes)")
 	flag.BoolVar(&dbg, "d", false, "debug logging")
+
+	flag.Var(&aKEXAlgs, "aK", `List of allowed KEX algs (eg. 'KEXAlgA KEXAlgB ... KEXAlgN') (default allow all)`)
+	flag.Var(&aCipherAlgs, "aC", `List of allowed ciphers (eg. 'CipherAlgA CipherAlgB ... CipherAlgN') (default allow all)`)
+	flag.Var(&aHMACAlgs, "aH", `List of allowed HMACs (eg. 'HMACAlgA HMACAlgB ... HMACAlgN') (default allow all)`)
+
 	flag.Parse()
 
 	if vopt {
@@ -486,6 +556,22 @@ func main() {
 		log.SetOutput(ioutil.Discard)
 	}
 
+	// Set up allowed algs, if specified (default allow all)
+	if len(aKEXAlgs) == 0 {
+		aKEXAlgs = []string{"KEX_all"}
+	}
+	logger.LogNotice(fmt.Sprintf("Allowed KEXAlgs: %v\n", aKEXAlgs)) // nolint: gosec,errcheck
+
+	if len(aCipherAlgs) == 0 {
+		aCipherAlgs = []string{"C_all"}
+	}
+	logger.LogNotice(fmt.Sprintf("Allowed CipherAlgs: %v\n", aCipherAlgs)) // nolint: gosec,errcheck
+
+	if len(aHMACAlgs) == 0 {
+		aHMACAlgs = []string{"H_all"}
+	}
+	logger.LogNotice(fmt.Sprintf("Allowed HMACAlgs: %v\n", aHMACAlgs)) // nolint: gosec,errcheck
+
 	// Set up handler for daemon signalling
 	exitCh := make(chan os.Signal, 1)
 	signal.Notify(exitCh, os.Signal(syscall.SIGTERM), os.Signal(syscall.SIGINT), os.Signal(syscall.SIGHUP), os.Signal(syscall.SIGUSR1), os.Signal(syscall.SIGUSR2))
@@ -522,9 +608,22 @@ func main() {
 	log.Println("Serving on", laddr)
 	for {
 		// Wait for a connection.
+		// Then check if client-proposed algs are allowed
 		conn, err := l.Accept()
 		if err != nil {
 			log.Printf("Accept() got error(%v), hanging up.\n", err)
+		} else if !aKEXAlgs.allowed(conn.KEX()) {
+			log.Printf("Accept() rejected for banned KEX alg %d, hanging up.\n", conn.KEX())
+			conn.SetStatus(xsnet.CSEKEXAlgDenied)
+			conn.Close()
+		} else if !aCipherAlgs.allowed(conn.CAlg()) {
+			log.Printf("Accept() rejected for banned Cipher alg %d, hanging up.\n", conn.CAlg())
+			conn.SetStatus(xsnet.CSECipherAlgDenied)
+			conn.Close()
+		} else if !aHMACAlgs.allowed(conn.HAlg()) {
+			log.Printf("Accept() rejected for banned HMAC alg %d, hanging up.\n", conn.HAlg())
+			conn.SetStatus(xsnet.CSEHMACAlgDenied)
+			conn.Close()
 		} else {
 			log.Println("Accepted client")
 

xsnet/consts.go

@@ -29,6 +29,7 @@ const (
 	KEX_NEWHOPE_SIMPLE // 'NewHopeLP-Simple' - https://eprint.iacr.org/2016/1157
 	KEX_resvd14
 	KEX_resvd15
+	KEX_invalid = 255
 )
 
 // Sent from client to server in order to specify which
@@ -44,6 +45,9 @@ const (
 	CSEExecFail        // cmd.Start() (exec) failed
 	CSEPtyExecFail     // pty.Start() (exec w/pty) failed
 	CSEPtyGetNameFail  // failed to obtain pty name
+	CSEKEXAlgDenied    // server rejected proposed KEX alg
+	CSECipherAlgDenied // server rejected proposed Cipher alg
+	CSEHMACAlgDenied   // server rejected proposed HMAC alg
 )
 
 // Extended (>255 UNIX exit status) codes

xsnet/net.go

@@ -71,6 +71,7 @@ type (
 	// Conn is a connection wrapping net.Conn with KEX & session state
 	Conn struct {
 		kex KEXAlg // KEX/KEM proposal (client -> server)
+
 		m *sync.Mutex // (internal)
 		c *net.Conn   // which also implements io.Reader, io.Writer, ...
 
@@ -105,6 +106,67 @@ func (t *TunEndpoint) String() string {
 	return fmt.Sprintf("[%d:%s:%d]", t.Lport, t.Peer, t.Rport)
 }
 
+func (k *KEXAlg) String() string {
+	switch *k {
+	case KEX_HERRADURA256:
+		return "KEX_HERRADURA256"
+	case KEX_HERRADURA512:
+		return "KEX_HERRADURA512"
+	case KEX_HERRADURA1024:
+		return "KEX_HERRADURA1024"
+	case KEX_HERRADURA2048:
+		return "KEX_HERRADURA2048"
+	case KEX_KYBER512:
+		return "KEX_KYBER512"
+	case KEX_KYBER768:
+		return "KEX_KYBER768"
+	case KEX_KYBER1024:
+		return "KEX_KYBER1024"
+	case KEX_NEWHOPE:
+		return "KEX_NEWHOPE"
+	case KEX_NEWHOPE_SIMPLE:
+		return "KEX_NEWHOPE_SIMPLE"
+	default:
+		return "KEX_ERR_UNK"
+	}
+}
+
+func (hc *Conn) CAlg() CSCipherAlg {
+	return CSCipherAlg(hc.cipheropts & 0x0FF)
+}
+
+func (c *CSCipherAlg) String() string {
+	switch *c & 0x0FF {
+	case CAlgAES256:
+		return "C_AES_256"
+	case CAlgTwofish128:
+		return "C_TWOFISH_128"
+	case CAlgBlowfish64:
+		return "C_BLOWFISH_64"
+	case CAlgCryptMT1:
+		return "C_CRYPTMT1"
+	case CAlgWanderer:
+		return "C_WANDERER"
+	default:
+		return "C_ERR_UNK"
+	}
+}
+
+func (hc *Conn) HAlg() CSHmacAlg {
+	return CSHmacAlg((hc.cipheropts >> 8) & 0x0FF)
+}
+
+func (h *CSHmacAlg) String() string {
+	switch (*h >> 8) & 0x0FF {
+	case HmacSHA256:
+		return "H_SHA256"
+	case HmacSHA512:
+		return "C_SHA512"
+	default:
+		return "H_ERR_UNK"
+	}
+}
+
 func _initLogging(d bool, c string, f logger.Priority) {
 	if Log == nil {
 		Log, _ = logger.New(f, fmt.Sprintf("%s:xsnet", c))
@@ -129,6 +191,10 @@ func (hc *Conn) Unlock() {
 	hc.m.Unlock()
 }
 
+func (hc Conn) KEX() KEXAlg {
+	return hc.kex
+}
+
 func (hc Conn) GetStatus() CSOType {
 	return *hc.closeStat
 }
@@ -935,6 +1001,9 @@ func (hl *HKExListener) Accept() (hc Conn, err error) {
 	default:
 		return Conn{}, err
 	}
+
+	// Finally, ensure alg proposed by client is allowed by server config
+	//if hc.kex.String() {
 	log.Println("[hc.Accept successful]")
 	return
 }