check inner packet srcIP against server-verified srcIP, Windows support

README.md

@@ -4,11 +4,19 @@ A hub-and-spoke VPN for IPv6
 
 ## Features
 * **Post-quantum security:** Uses [HPKE](https://datatracker.ietf.org/doc/html/rfc9180/)([XWingMLKEM768X25519](https://datatracker.ietf.org/doc/html/draft-connolly-cfrg-xwing-kem/), [HKDF-SHA-256](https://en.wikipedia.org/wiki/HKDF)) + [XChaCha20-Poly1305](https://en.wikipedia.org/wiki/ChaCha20-Poly1305#XChaCha20-Poly1305_%E2%80%93_extended_nonce_variant) for encryption and [ML-DSA-44](https://nvlpubs.nist.gov/nistpubs/fips/nist.fips.204.pdf) for signatures.
+* **NAT-resistant architecture:** Any device with Internet access can easily join the network.
+* **Cross-platform-ish:** Tested on Linux and Windows. macOS should probably work too.
 
 ## Protocol
 
-See [proto.go](https://git.ton1.dev/toni/baalvpn/src/branch/main/shared/proto.go)
+See [proto.go](https://git.ton1.dev/toni/baalvpn/src/branch/main/shared/proto.go) for details
+
+### Known limitations
+* Compromised server could give out fake pubkeys allowing a MITM attack and decrypting the peer-to-peer traffic
+* The keys are rotated only on client and server restart
+* The protocol is vulnerable to replay attacks
 
 ## Third-party dependencies
-* [`github.com/songgao/water`](https://github.com/songgao/water) - cross-platform wrapper around TUN interfaces
+* [`github.com/songgao/water`](https://github.com/songgao/water) - wrapper around TUN interfaces for \*nix
+* [`golang.zx2c4.com/wintun`](https://git.zx2c4.com/wintun-go) - wrapper around `wintun.dll`
 * [`github.com/cloudflare/circl`](https://github.com/cloudflare/circl) - used for ML-DSA, hopefully [not for long](https://github.com/golang/go/issues/77626)

client/main.go

@@ -8,26 +8,21 @@ import (
 	"encoding/hex"
 	"log"
 	"net"
-	"os"
-	"os/exec"
 	"sync"
 	"time"
 
 	"baalvpn/shared"
 
 	"github.com/cloudflare/circl/sign/mldsa/mldsa44"
-	"github.com/songgao/water"
 )
 
 // TODO: parse some sort of config+key file
 const (
 	SERVER_IP     = "172.20.12.47"
-	IFACE_NAME    = "baalvpn"
 	SERVER_PUBKEY = "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"
 )
 
 var (
-	iface        *water.Interface
 	conn         *net.UDPConn
 	serverAddr   *net.UDPAddr
 	internalIP   net.IP
@@ -43,8 +38,8 @@ var (
 )
 
 func main() {
-	if os.Geteuid() != 0 {
+	if !isAdmin() {
-		panic("root permissions needed")
+		panic("this program must be ran with administrative privileges")
 	}
 
 	listenAddr, err := net.ResolveUDPAddr("udp", ":38000")
@@ -157,23 +152,40 @@ func handleIncomingPkt(pkt []byte) {
 		srcIP := net.IP(pkt[52:68]).String()
 
 		sessionKey := getOrEstablishSessionKey(srcIP)
+		if sessionKey == nil {
+			return
+		}
 
 		decryptedPkt, err := DecryptSym(sessionKey, pkt[68:])
 		if err != nil {
 			panic(err)
 		}
 
+		if len(decryptedPkt) >= 24 {
+			innerSrcIP := net.IP(decryptedPkt[8:24]).String()
+			if innerSrcIP != srcIP {
+				return
+			}
+		}
+
 		log.Println("received pkt:", hex.EncodeToString(decryptedPkt))
-		if _, err := iface.Write(decryptedPkt); err != nil {
+		if err := writePkt(decryptedPkt); err != nil {
 			log.Println(err)
 		}
 	case shared.BROADCAST_PKT:
-		decryptedPkt, err := DecryptSym(multicastKey, pkt[36:])
+		decryptedPkt, err := DecryptSym(multicastKey, pkt[52:])
 		if err != nil {
 			panic(err)
 		}
+		if len(decryptedPkt) >= 24 {
+			outerSrcIP := net.IP(pkt[36:52]).String()
+			innerSrcIP := net.IP(decryptedPkt[8:24]).String()
+			if innerSrcIP != outerSrcIP {
+				return
+			}
+		}
 		log.Println("received broadcast:", hex.EncodeToString(decryptedPkt))
-		if _, err := iface.Write(decryptedPkt); err != nil {
+		if err := writePkt(decryptedPkt); err != nil {
 			log.Println(err)
 		}
 	case shared.RESP_GET_PUBKEY:
@@ -226,9 +238,10 @@ func getOrEstablishSessionKey(ip string) []byte {
 		return key
 	}
 
+	log.Println("lets try to get " + ip + "'s pubkey")
+
 	// TODO: this definitely shouldnt block the main thread
-	// TODO: this should try like 10 times tops since server doesnt respond at all if it doesnt have the pubkey
+	for range 30 {
-	for {
 		// request pubkey every 50ms
 		time.Sleep(50 * time.Millisecond)
 		peerPubKey, ok := peerPubKeys.GetOK(ip)
@@ -250,51 +263,41 @@ func getOrEstablishSessionKey(ip string) []byte {
 
 		send(buildAuthPkt(shared.REQ_ESTABLISH, net.ParseIP(ip), internalIP, ciphertext))
 
-		for {
+		success := false
+		for range 30 {
 			// TODO: eww
 			time.Sleep(50 * time.Millisecond)
 			if peerEstablishAcks.Get(ip) {
 				peerEstablishAcks.Delete(ip)
+				success = true
 				break
 			}
 		}
+		if !success {
+			log.Println("failed to establish")
+			return nil
+		}
 
 		peerSessionKeys.Set(ip, sessionKey)
 		return sessionKey
 	}
-}
 
-func setupInterface() {
+	log.Println("failed to get the pubkey")
-	config := water.Config{DeviceType: water.TUN}
+	return nil
-	config.Name = IFACE_NAME
-
-	var err error
-	iface, err = water.New(config)
-	if err != nil {
-		panic(err)
-	}
-
-	if err := exec.Command("ip", "addr", "add", internalIP.String()+"/32", "dev", IFACE_NAME).Run(); err != nil {
-		panic(err)
-	}
-	if err := exec.Command("ip", "link", "set", "dev", IFACE_NAME, "up").Run(); err != nil {
-		panic(err)
-	}
 }
 
 func relayPackets() {
 	log.Println("Listening for packets...")
 
 	for {
-		pkt := make([]byte, 2000)
+		pkt, err := readPkt()
-		n, err := iface.Read([]byte(pkt))
 		if err != nil {
 			panic(err)
 		}
-		pkt = pkt[:n]
 
 		version := pkt[0] >> 4
 		if version != 6 {
+			releasePkt(pkt)
 			continue
 		}
 
@@ -306,9 +309,13 @@ func relayPackets() {
 				panic(err)
 			}
 
-			send(buildAuthPkt(shared.BROADCAST_PKT, encryptedPkt))
+			send(buildAuthPkt(shared.BROADCAST_PKT, internalIP, encryptedPkt))
 		} else {
 			destSessionKey := getOrEstablishSessionKey(destIP)
+			if destSessionKey == nil {
+				releasePkt(pkt)
+				continue
+			}
 
 			encryptedPkt, err := EncryptSym(destSessionKey, pkt)
 			if err != nil {
@@ -317,6 +324,8 @@ func relayPackets() {
 
 			send(buildAuthPkt(shared.UNICAST_PKT, net.ParseIP(destIP), internalIP, encryptedPkt))
 		}
+
+		releasePkt(pkt)
 	}
 }
 

client/os.go

@@ -0,0 +1,61 @@
+//go:build linux || darwin
+
+package main
+
+import (
+	"os"
+	"os/exec"
+	"runtime"
+
+	"github.com/songgao/water"
+)
+
+var iface *water.Interface
+
+func isAdmin() bool {
+	return os.Geteuid() == 0
+}
+
+func setupInterface() {
+	config := water.Config{DeviceType: water.TUN}
+	if runtime.GOOS == "linux" {
+		config.Name = "baalvpn"
+	} else {
+		panic("TODO")
+	}
+
+	var err error
+	iface, err = water.New(config)
+	if err != nil {
+		panic(err)
+	}
+
+	if runtime.GOOS == "linux" {
+		if err := exec.Command("ip", "addr", "add", internalIP.String()+"/32", "dev", "baalvpn").Run(); err != nil {
+			panic(err)
+		}
+		if err := exec.Command("ip", "link", "set", "dev", "baalvpn", "up").Run(); err != nil {
+			panic(err)
+		}
+	} else {
+		if err := exec.Command("ifconfig", iface.Name(), "inet6", internalIP.String(), internalIP.String(), "prefixlen", "128", "up").Run(); err != nil {
+			panic(err)
+		}
+	}
+}
+
+func writePkt(pkt []byte) error {
+	_, err := iface.Write(pkt)
+	return err
+}
+
+func readPkt() ([]byte, error) {
+	pkt := make([]byte, 2000)
+	n, err := iface.Read(pkt)
+	if err != nil {
+		return nil, err
+	}
+	return pkt[:n], nil
+}
+
+func releasePkt(pkt []byte) {}

client/os_windows.go

@@ -0,0 +1,76 @@
+//go:build windows
+
+package main
+
+import (
+	"os"
+	"os/exec"
+
+	"golang.org/x/sys/windows"
+	"golang.zx2c4.com/wintun"
+)
+
+var session wintun.Session
+var readWait windows.Handle
+
+func isAdmin() bool {
+	f, err := os.Open("\\\\.\\PHYSICALDRIVE0")
+	if err != nil {
+		return false
+	}
+	f.Close()
+	return true
+}
+
+func setupInterface() {
+	adapter, err := wintun.CreateAdapter("baalvpn", "Wintun", nil)
+	if err != nil {
+		panic(err)
+	}
+
+	session, err = adapter.StartSession(0x800000)
+	if err != nil {
+		panic(err)
+	}
+	readWait = session.ReadWaitEvent()
+
+	if err := exec.Command("netsh", "interface", "ipv6", "add", "address", "interface=baalvpn", "address="+internalIP.String()).Run(); err != nil {
+		panic(err)
+	}
+	if err := exec.Command("netsh", "interface", "ipv6", "set", "interface", "interface=baalvpn", "forwarding=disabled").Run(); err != nil {
+		panic(err)
+	}
+	if err := exec.Command("netsh", "interface", "ipv6", "add", "route", "fd00:baa1::/32", "interface=baalvpn").Run(); err != nil {
+		panic(err)
+	}
+	if err := exec.Command("netsh", "advfirewall", "firewall", "add", "rule", "name=BaalVPN In", "dir=in", "action=allow", "remoteip=fd00:baa1::/32").Run(); err != nil {
+		panic(err)
+	}
+	if err := exec.Command("netsh", "advfirewall", "firewall", "add", "rule", "name=BaalVPN Out", "dir=out", "action=allow", "remoteip=fd00:baa1::/32").Run(); err != nil {
+		panic(err)
+	}
+}
+
+func writePkt(pkt []byte) error {
+	sp, err := session.AllocateSendPacket(len(pkt))
+	if err != nil {
+		return err
+	}
+	copy(sp, pkt)
+	session.SendPacket(sp)
+	return nil
+}
+
+func readPkt() ([]byte, error) {
+	for {
+		pkt, err := session.ReceivePacket()
+		if err == nil {
+			return pkt, nil
+		}
+		windows.WaitForSingleObject(readWait, windows.INFINITE)
+	}
+}
+
+func releasePkt(pkt []byte) {
+	session.ReleaseReceivePacket(pkt)
+}

go.mod

@@ -6,6 +6,6 @@ require (
 	github.com/cloudflare/circl v1.6.4
 	github.com/songgao/water v0.0.0-20200317203138-2b4b6d7c09d8
 	golang.org/x/crypto v0.54.0
+	golang.org/x/sys v0.47.0
+	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2
 )
-
-require golang.org/x/sys v0.47.0 // indirect

go.sum

@@ -6,3 +6,5 @@ golang.org/x/crypto v0.54.0 h1:YLIA59K4fiNzHzjnZt2tUJQjQtUWfWbeHBqKtk3eScw=
 golang.org/x/crypto v0.54.0/go.mod h1:KWL8ny2AZdGR2cWmzeHrp2azQPGogOv+HeQaVEXC2dk=
 golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
 golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 h1:B82qJJgjvYKsXS9jeunTOisW56dUokqW/FOteYJJ/yg=
+golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2/go.mod h1:deeaetjYA+DHMHg+sMSMI58GrEteJUUzzw7en6TJQcI=

server/main.go

@@ -217,7 +217,7 @@ func handleReq(req []byte, addr *net.UDPAddr) {
 			log.Println(srcIP + " -/> " + destIP + " (unrecognized IP)")
 		}
 	case shared.BROADCAST_PKT:
-		if len(req) <= 36 {
+		if len(req) <= 52 {
 			log.Println("BROADCAST_PKT packet too short")
 			return
 		}
@@ -227,6 +227,12 @@ func handleReq(req []byte, addr *net.UDPAddr) {
 			return
 		}
 
+		srcIP := net.IP(req[36:52]).String()
+		if srcIP != peer.InternalIP {
+			log.Println("rejected spoofed srcIP in BROADCAST_PKT")
+			return
+		}
+
 		mac := hmac.New(sha256.New, peer.AuthSecret)
 		mac.Write(req[36:])
 		if !hmac.Equal(mac.Sum(nil), req[4:36]) {
@@ -241,17 +247,23 @@ func handleReq(req []byte, addr *net.UDPAddr) {
 			log.Println("REQ_GET_PUBKEY packet too short")
 			return
 		}
-		peerIP := net.IP(req[36:52]).String()
-		peer := peersByInternal.Get(peerIP)
-		if peer != nil {
-			mac := hmac.New(sha256.New, peer.AuthSecret)
-			mac.Write(req[36:])
-			if !hmac.Equal(mac.Sum(nil), req[4:36]) {
-				log.Println("failed to authenticate REQ_GET_PUBKEY")
-				return
-			}
 
-			pubKey, err := hex.DecodeString(peer.HexPublicKey)
+		peer := peers.Get(addr.String())
+		if peer == nil {
+			log.Println("REQ_GET_PUBKEY from unregistered peer:", addr.String())
+			return
+		}
+		mac := hmac.New(sha256.New, peer.AuthSecret)
+		mac.Write(req[36:])
+		if !hmac.Equal(mac.Sum(nil), req[4:36]) {
+			log.Println("failed to authenticate REQ_GET_PUBKEY")
+			return
+		}
+
+		peerIP := net.IP(req[36:52]).String()
+		targetPeer := peersByInternal.Get(peerIP)
+		if targetPeer != nil {
+			pubKey, err := hex.DecodeString(targetPeer.HexPublicKey)
 			if err != nil {
 				panic(err) // should never happen
 			}

shared/proto.go

@@ -12,7 +12,7 @@ const PROTO_VERSION uint16 = 1
 // multicastKey  - key shared between everyone for encrypting multicast packets
 // authSecret    - secret assigned to a client for authenticating subsequent requests
 
-// SYM  = XChaCha20‑Poly1305 with nonce prepended
+// SYM  = XChaCha20-Poly1305 with nonce prepended
 // HMAC = HMAC-SHA-256
 // hpke = HPKE(MLKEM768X25519, ChaCha20Poly1305, HKDF-SHA-256)
 // ds   = ML-DSA
@@ -49,7 +49,7 @@ const (
 	// [ HMAC(authSecret, rest) - 32 bytes ] [ destIP - 16 bytes ] [ srcIP - 16 bytes ] [ SYM(sessionKey, pkt) ]
 	UNICAST_PKT
 	// (client -> server -> *) broadcasts an encrypted packet
-	// [ HMAC(authSecret, rest) - 32 bytes ] [ SYM(multicastKey, pkt) ]
+	// [ HMAC(authSecret, rest) - 32 bytes ] [ srcIP - 16 bytes ] [ SYM(multicastKey, pkt) ]
 	BROADCAST_PKT
 )