Merge pull request #208 from fosrl/icmp2

Support ICMP test requests for clients

Dockerfile

@@ -20,7 +20,7 @@ RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /newt
 
 FROM alpine:3.23 AS runner
 
-RUN apk --no-cache add ca-certificates tzdata
+RUN apk --no-cache add ca-certificates tzdata iputils
 
 COPY --from=builder /newt /usr/local/bin/
 COPY entrypoint.sh /

clients/clients.go

@@ -40,12 +40,13 @@ type Target struct {
 	SourcePrefix string      `json:"sourcePrefix"`
 	DestPrefix   string      `json:"destPrefix"`
 	RewriteTo    string      `json:"rewriteTo,omitempty"`
+	DisableIcmp  bool        `json:"disableIcmp,omitempty"`
 	PortRange    []PortRange `json:"portRange,omitempty"`
 }
 
 type PortRange struct {
-	Min uint16 `json:"min"`
-	Max uint16 `json:"max"`
+	Min      uint16 `json:"min"`
+	Max      uint16 `json:"max"`
 	Protocol string `json:"protocol"` // "tcp" or "udp"
 }
 
@@ -593,8 +594,9 @@ func (s *WireGuardService) ensureWireguardInterface(wgconfig WgConfig) error {
 		s.dns,
 		s.mtu,
 		netstack2.NetTunOptions{
-			EnableTCPProxy: true,
-			EnableUDPProxy: true,
+			EnableTCPProxy:  true,
+			EnableUDPProxy:  true,
+			EnableICMPProxy: true,
 		},
 	)
 	if err != nil {
@@ -700,13 +702,13 @@ func (s *WireGuardService) ensureTargets(targets []Target) error {
 		var portRanges []netstack2.PortRange
 		for _, pr := range target.PortRange {
 			portRanges = append(portRanges, netstack2.PortRange{
-				Min: pr.Min,
-				Max: pr.Max,
+				Min:      pr.Min,
+				Max:      pr.Max,
 				Protocol: pr.Protocol,
 			})
 		}
 
-		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges)
+		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges, target.DisableIcmp)
 
 		logger.Info("Added target subnet from %s to %s rewrite to %s with port ranges: %v", target.SourcePrefix, target.DestPrefix, target.RewriteTo, target.PortRange)
 	}
@@ -1094,10 +1096,11 @@ func (s *WireGuardService) handleAddTarget(msg websocket.WSMessage) {
 			portRanges = append(portRanges, netstack2.PortRange{
 				Min: pr.Min,
 				Max: pr.Max,
+				Protocol:    pr.Protocol,
 			})
 		}
 
-		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges)
+		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges, target.DisableIcmp)
 
 		logger.Info("Added target subnet from %s to %s rewrite to %s with port ranges: %v", target.SourcePrefix, target.DestPrefix, target.RewriteTo, target.PortRange)
 	}
@@ -1209,12 +1212,13 @@ func (s *WireGuardService) handleUpdateTarget(msg websocket.WSMessage) {
 		var portRanges []netstack2.PortRange
 		for _, pr := range target.PortRange {
 			portRanges = append(portRanges, netstack2.PortRange{
-				Min: pr.Min,
-				Max: pr.Max,
+				Min:         pr.Min,
+				Max:         pr.Max,
+				Protocol:    pr.Protocol,
 			})
 		}
 
-		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges)
+		s.tnet.AddProxySubnetRule(sourcePrefix, destPrefix, target.RewriteTo, portRanges, target.DisableIcmp)
 		logger.Info("Added target subnet from %s to %s rewrite to %s with port ranges: %v", target.SourcePrefix, target.DestPrefix, target.RewriteTo, target.PortRange)
 	}
 }

netstack2/handlers.go

@@ -10,12 +10,18 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"net/netip"
+	"os/exec"
 	"sync"
 	"time"
 
 	"github.com/fosrl/newt/logger"
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
+	"gvisor.dev/gvisor/pkg/tcpip/checksum"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/udp"
@@ -58,6 +64,9 @@ const (
 
 	// Buffer size for copying data
 	bufferSize = 32 * 1024
+
+	// icmpTimeout is the default timeout for ICMP ping requests.
+	icmpTimeout = 5 * time.Second
 )
 
 // TCPHandler handles TCP connections from netstack
@@ -72,6 +81,12 @@ type UDPHandler struct {
 	proxyHandler *ProxyHandler
 }
 
+// ICMPHandler handles ICMP packets from netstack
+type ICMPHandler struct {
+	stack        *stack.Stack
+	proxyHandler *ProxyHandler
+}
+
 // NewTCPHandler creates a new TCP handler
 func NewTCPHandler(s *stack.Stack, ph *ProxyHandler) *TCPHandler {
 	return &TCPHandler{stack: s, proxyHandler: ph}
@@ -82,6 +97,11 @@ func NewUDPHandler(s *stack.Stack, ph *ProxyHandler) *UDPHandler {
 	return &UDPHandler{stack: s, proxyHandler: ph}
 }
 
+// NewICMPHandler creates a new ICMP handler
+func NewICMPHandler(s *stack.Stack, ph *ProxyHandler) *ICMPHandler {
+	return &ICMPHandler{stack: s, proxyHandler: ph}
+}
+
 // InstallTCPHandler installs the TCP forwarder on the stack
 func (h *TCPHandler) InstallTCPHandler() error {
 	tcpForwarder := tcp.NewForwarder(h.stack, defaultWndSize, maxConnAttempts, func(r *tcp.ForwarderRequest) {
@@ -348,3 +368,334 @@ func copyPacketData(dst, src net.PacketConn, to net.Addr, timeout time.Duration)
 		dst.SetReadDeadline(time.Now().Add(timeout))
 	}
 }
+
+// InstallICMPHandler installs the ICMP handler on the stack
+func (h *ICMPHandler) InstallICMPHandler() error {
+	h.stack.SetTransportProtocolHandler(header.ICMPv4ProtocolNumber, h.handleICMPPacket)
+	logger.Info("ICMP Handler: Installed ICMP protocol handler")
+	return nil
+}
+
+// handleICMPPacket handles incoming ICMP packets
+func (h *ICMPHandler) handleICMPPacket(id stack.TransportEndpointID, pkt *stack.PacketBuffer) bool {
+	logger.Debug("ICMP Handler: Received ICMP packet from %s to %s", id.RemoteAddress, id.LocalAddress)
+
+	// Get the ICMP header from the packet
+	icmpData := pkt.TransportHeader().Slice()
+	if len(icmpData) < header.ICMPv4MinimumSize {
+		logger.Debug("ICMP Handler: Packet too small for ICMP header: %d bytes", len(icmpData))
+		return false
+	}
+
+	icmpHdr := header.ICMPv4(icmpData)
+	icmpType := icmpHdr.Type()
+	icmpCode := icmpHdr.Code()
+
+	logger.Debug("ICMP Handler: Type=%d, Code=%d, Ident=%d, Seq=%d",
+		icmpType, icmpCode, icmpHdr.Ident(), icmpHdr.Sequence())
+
+	// Only handle Echo Request (ping)
+	if icmpType != header.ICMPv4Echo {
+		logger.Debug("ICMP Handler: Ignoring non-echo ICMP type: %d", icmpType)
+		return false
+	}
+
+	// Extract source and destination addresses
+	srcIP := id.RemoteAddress.String()
+	dstIP := id.LocalAddress.String()
+
+	logger.Info("ICMP Handler: Echo Request from %s to %s (ident=%d, seq=%d)",
+		srcIP, dstIP, icmpHdr.Ident(), icmpHdr.Sequence())
+
+	// Convert to netip.Addr for subnet matching
+	srcAddr, err := netip.ParseAddr(srcIP)
+	if err != nil {
+		logger.Debug("ICMP Handler: Failed to parse source IP %s: %v", srcIP, err)
+		return false
+	}
+	dstAddr, err := netip.ParseAddr(dstIP)
+	if err != nil {
+		logger.Debug("ICMP Handler: Failed to parse dest IP %s: %v", dstIP, err)
+		return false
+	}
+
+	// Check subnet rules (use port 0 for ICMP since it doesn't have ports)
+	if h.proxyHandler == nil {
+		logger.Debug("ICMP Handler: No proxy handler configured")
+		return false
+	}
+
+	matchedRule := h.proxyHandler.subnetLookup.Match(srcAddr, dstAddr, 0, header.ICMPv4ProtocolNumber)
+	if matchedRule == nil {
+		logger.Debug("ICMP Handler: No matching subnet rule for %s -> %s", srcIP, dstIP)
+		return false
+	}
+
+	logger.Info("ICMP Handler: Matched subnet rule for %s -> %s", srcIP, dstIP)
+
+	// Determine actual destination (with possible rewrite)
+	actualDstIP := dstIP
+	if matchedRule.RewriteTo != "" {
+		resolvedAddr, err := h.proxyHandler.resolveRewriteAddress(matchedRule.RewriteTo)
+		if err != nil {
+			logger.Info("ICMP Handler: Failed to resolve rewrite address %s: %v", matchedRule.RewriteTo, err)
+		} else {
+			actualDstIP = resolvedAddr.String()
+			logger.Info("ICMP Handler: Using rewritten destination %s (original: %s)", actualDstIP, dstIP)
+		}
+	}
+
+	// Get the full ICMP payload (including the data after the header)
+	icmpPayload := pkt.Data().AsRange().ToSlice()
+
+	// Handle the ping in a goroutine to avoid blocking
+	go h.proxyPing(srcIP, dstIP, actualDstIP, icmpHdr.Ident(), icmpHdr.Sequence(), icmpPayload)
+
+	return true
+}
+
+// proxyPing sends a ping to the actual destination and injects the reply back
+func (h *ICMPHandler) proxyPing(srcIP, originalDstIP, actualDstIP string, ident, seq uint16, payload []byte) {
+	logger.Debug("ICMP Handler: Proxying ping from %s to %s (actual: %s), ident=%d, seq=%d",
+		srcIP, originalDstIP, actualDstIP, ident, seq)
+
+	// Try three methods in order: ip4:icmp -> udp4 -> ping command
+	// Track which method succeeded so we can handle identifier matching correctly
+	method, success := h.tryICMPMethods(actualDstIP, ident, seq, payload)
+
+	if !success {
+		logger.Info("ICMP Handler: All ping methods failed for %s", actualDstIP)
+		return
+	}
+
+	logger.Info("ICMP Handler: Ping successful to %s using %s, injecting reply (ident=%d, seq=%d)",
+		actualDstIP, method, ident, seq)
+
+	// Build the reply packet to inject back into the netstack
+	// The reply should appear to come from the original destination (before rewrite)
+	h.injectICMPReply(srcIP, originalDstIP, ident, seq, payload)
+}
+
+// tryICMPMethods tries all available ICMP methods in order
+func (h *ICMPHandler) tryICMPMethods(actualDstIP string, ident, seq uint16, payload []byte) (string, bool) {
+	if h.tryRawICMP(actualDstIP, ident, seq, payload, false) {
+		return "raw ICMP", true
+	}
+	if h.tryUnprivilegedICMP(actualDstIP, ident, seq, payload) {
+		return "unprivileged ICMP", true
+	}
+	if h.tryPingCommand(actualDstIP, ident, seq, payload) {
+		return "ping command", true
+	}
+	return "", false
+}
+
+// tryRawICMP attempts to ping using raw ICMP sockets (requires CAP_NET_RAW or root)
+func (h *ICMPHandler) tryRawICMP(actualDstIP string, ident, seq uint16, payload []byte, ignoreIdent bool) bool {
+	conn, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
+	if err != nil {
+		logger.Debug("ICMP Handler: Raw ICMP socket not available: %v", err)
+		return false
+	}
+	defer conn.Close()
+
+	logger.Debug("ICMP Handler: Using raw ICMP socket")
+	return h.sendAndReceiveICMP(conn, actualDstIP, ident, seq, payload, false, ignoreIdent)
+}
+
+// tryUnprivilegedICMP attempts to ping using unprivileged ICMP (requires ping_group_range configured)
+func (h *ICMPHandler) tryUnprivilegedICMP(actualDstIP string, ident, seq uint16, payload []byte) bool {
+	conn, err := icmp.ListenPacket("udp4", "0.0.0.0")
+	if err != nil {
+		logger.Debug("ICMP Handler: Unprivileged ICMP socket not available: %v", err)
+		return false
+	}
+	defer conn.Close()
+
+	logger.Debug("ICMP Handler: Using unprivileged ICMP socket")
+	// Unprivileged ICMP doesn't let us control the identifier, so we ignore it in matching
+	return h.sendAndReceiveICMP(conn, actualDstIP, ident, seq, payload, true, true)
+}
+
+// sendAndReceiveICMP sends an ICMP echo request and waits for the reply
+func (h *ICMPHandler) sendAndReceiveICMP(conn *icmp.PacketConn, actualDstIP string, ident, seq uint16, payload []byte, isUnprivileged bool, ignoreIdent bool) bool {
+	// Build the ICMP echo request message
+	echoMsg := &icmp.Message{
+		Type: ipv4.ICMPTypeEcho,
+		Code: 0,
+		Body: &icmp.Echo{
+			ID:   int(ident),
+			Seq:  int(seq),
+			Data: payload,
+		},
+	}
+
+	msgBytes, err := echoMsg.Marshal(nil)
+	if err != nil {
+		logger.Debug("ICMP Handler: Failed to marshal ICMP message: %v", err)
+		return false
+	}
+
+	// Resolve destination address based on socket type
+	var writeErr error
+	if isUnprivileged {
+		// For unprivileged ICMP, use UDP-style addressing
+		udpAddr := &net.UDPAddr{IP: net.ParseIP(actualDstIP)}
+		logger.Debug("ICMP Handler: Sending ping to %s (unprivileged)", udpAddr.String())
+		conn.SetDeadline(time.Now().Add(icmpTimeout))
+		_, writeErr = conn.WriteTo(msgBytes, udpAddr)
+	} else {
+		// For raw ICMP, use IP addressing
+		dst, err := net.ResolveIPAddr("ip4", actualDstIP)
+		if err != nil {
+			logger.Debug("ICMP Handler: Failed to resolve destination %s: %v", actualDstIP, err)
+			return false
+		}
+		logger.Debug("ICMP Handler: Sending ping to %s (raw)", dst.String())
+		conn.SetDeadline(time.Now().Add(icmpTimeout))
+		_, writeErr = conn.WriteTo(msgBytes, dst)
+	}
+
+	if writeErr != nil {
+		logger.Debug("ICMP Handler: Failed to send ping to %s: %v", actualDstIP, writeErr)
+		return false
+	}
+
+	logger.Debug("ICMP Handler: Ping sent to %s, waiting for reply (ident=%d, seq=%d)", actualDstIP, ident, seq)
+
+	// Wait for reply - loop to filter out non-matching packets
+	replyBuf := make([]byte, 1500)
+
+	for {
+		n, peer, err := conn.ReadFrom(replyBuf)
+		if err != nil {
+			logger.Debug("ICMP Handler: Failed to receive ping reply from %s: %v", actualDstIP, err)
+			return false
+		}
+
+		logger.Debug("ICMP Handler: Received %d bytes from %s", n, peer.String())
+
+		// Parse the reply
+		replyMsg, err := icmp.ParseMessage(1, replyBuf[:n])
+		if err != nil {
+			logger.Debug("ICMP Handler: Failed to parse ICMP message: %v", err)
+			continue
+		}
+
+		// Check if it's an echo reply (type 0), not an echo request (type 8)
+		if replyMsg.Type != ipv4.ICMPTypeEchoReply {
+			logger.Debug("ICMP Handler: Received non-echo-reply type: %v, continuing to wait", replyMsg.Type)
+			continue
+		}
+
+		reply, ok := replyMsg.Body.(*icmp.Echo)
+		if !ok {
+			logger.Debug("ICMP Handler: Invalid echo reply body type, continuing to wait")
+			continue
+		}
+
+		// Verify the sequence matches what we sent
+		// For unprivileged ICMP, the kernel controls the identifier, so we only check sequence
+		if reply.Seq != int(seq) {
+			logger.Debug("ICMP Handler: Reply seq mismatch: got seq=%d, want seq=%d", reply.Seq, seq)
+			continue
+		}
+		
+		if !ignoreIdent && reply.ID != int(ident) {
+			logger.Debug("ICMP Handler: Reply ident mismatch: got ident=%d, want ident=%d", reply.ID, ident)
+			continue
+		}
+
+		// Found matching reply
+		logger.Debug("ICMP Handler: Received valid echo reply")
+		return true
+	}
+}
+
+// tryPingCommand attempts to ping using the system ping command (always works, but less control)
+func (h *ICMPHandler) tryPingCommand(actualDstIP string, ident, seq uint16, payload []byte) bool {
+	logger.Debug("ICMP Handler: Attempting to use system ping command")
+
+	ctx, cancel := context.WithTimeout(context.Background(), icmpTimeout)
+	defer cancel()
+
+	// Send one ping with timeout
+	// -c 1: count = 1 packet
+	// -W 5: timeout = 5 seconds
+	// -q: quiet output (just summary)
+	cmd := exec.CommandContext(ctx, "ping", "-c", "1", "-W", "5", "-q", actualDstIP)
+	output, err := cmd.CombinedOutput()
+
+	if err != nil {
+		logger.Debug("ICMP Handler: System ping command failed: %v, output: %s", err, string(output))
+		return false
+	}
+
+	logger.Debug("ICMP Handler: System ping command succeeded")
+	return true
+}
+
+// injectICMPReply creates an ICMP echo reply packet and queues it to be sent back through the tunnel
+func (h *ICMPHandler) injectICMPReply(dstIP, srcIP string, ident, seq uint16, payload []byte) {
+	logger.Debug("ICMP Handler: Creating reply from %s to %s (ident=%d, seq=%d)",
+		srcIP, dstIP, ident, seq)
+
+	// Parse addresses
+	srcAddr, err := netip.ParseAddr(srcIP)
+	if err != nil {
+		logger.Info("ICMP Handler: Failed to parse source IP for reply: %v", err)
+		return
+	}
+	dstAddr, err := netip.ParseAddr(dstIP)
+	if err != nil {
+		logger.Info("ICMP Handler: Failed to parse dest IP for reply: %v", err)
+		return
+	}
+
+	// Calculate total packet size
+	ipHeaderLen := header.IPv4MinimumSize
+	icmpHeaderLen := header.ICMPv4MinimumSize
+	totalLen := ipHeaderLen + icmpHeaderLen + len(payload)
+
+	// Create the packet buffer
+	pkt := make([]byte, totalLen)
+
+	// Build IPv4 header
+	ipHdr := header.IPv4(pkt[:ipHeaderLen])
+	ipHdr.Encode(&header.IPv4Fields{
+		TotalLength: uint16(totalLen),
+		TTL:         64,
+		Protocol:    uint8(header.ICMPv4ProtocolNumber),
+		SrcAddr:     tcpip.AddrFrom4(srcAddr.As4()),
+		DstAddr:     tcpip.AddrFrom4(dstAddr.As4()),
+	})
+	ipHdr.SetChecksum(^ipHdr.CalculateChecksum())
+
+	// Build ICMP header
+	icmpHdr := header.ICMPv4(pkt[ipHeaderLen : ipHeaderLen+icmpHeaderLen])
+	icmpHdr.SetType(header.ICMPv4EchoReply)
+	icmpHdr.SetCode(0)
+	icmpHdr.SetIdent(ident)
+	icmpHdr.SetSequence(seq)
+
+	// Copy payload
+	copy(pkt[ipHeaderLen+icmpHeaderLen:], payload)
+
+	// Calculate ICMP checksum (covers ICMP header + payload)
+	icmpHdr.SetChecksum(0)
+	icmpData := pkt[ipHeaderLen:]
+	icmpHdr.SetChecksum(^checksum.Checksum(icmpData, 0))
+
+	logger.Debug("ICMP Handler: Built reply packet, total length=%d", totalLen)
+
+	// Queue the packet to be sent back through the tunnel
+	if h.proxyHandler != nil {
+		if h.proxyHandler.QueueICMPReply(pkt) {
+			logger.Info("ICMP Handler: Queued echo reply packet for transmission")
+		} else {
+			logger.Info("ICMP Handler: Failed to queue echo reply packet")
+		}
+	} else {
+		logger.Info("ICMP Handler: Cannot queue reply - proxy handler not available")
+	}
+}

netstack2/proxy.go

@@ -43,6 +43,7 @@ type PortRange struct {
 type SubnetRule struct {
 	SourcePrefix netip.Prefix // Source IP prefix (who is sending)
 	DestPrefix   netip.Prefix // Destination IP prefix (where it's going)
+	DisableIcmp  bool         // If true, ICMP traffic is blocked for this subnet
 	RewriteTo    string       // Optional rewrite address for DNAT - can be IP/CIDR or domain name
 	PortRanges   []PortRange  // empty slice means all ports allowed
 }
@@ -69,7 +70,7 @@ func NewSubnetLookup() *SubnetLookup {
 // AddSubnet adds a subnet rule with source and destination prefixes and optional port restrictions
 // If portRanges is nil or empty, all ports are allowed for this subnet
 // rewriteTo can be either an IP/CIDR (e.g., "192.168.1.1/32") or a domain name (e.g., "example.com")
-func (sl *SubnetLookup) AddSubnet(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange) {
+func (sl *SubnetLookup) AddSubnet(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange, disableIcmp bool) {
 	sl.mu.Lock()
 	defer sl.mu.Unlock()
 
@@ -81,6 +82,7 @@ func (sl *SubnetLookup) AddSubnet(sourcePrefix, destPrefix netip.Prefix, rewrite
 	sl.rules[key] = &SubnetRule{
 		SourcePrefix: sourcePrefix,
 		DestPrefix:   destPrefix,
+		DisableIcmp:  disableIcmp,
 		RewriteTo:    rewriteTo,
 		PortRanges:   portRanges,
 	}
@@ -123,6 +125,11 @@ func (sl *SubnetLookup) Match(srcIP, dstIP netip.Addr, port uint16, proto tcpip.
 			continue
 		}
 
+		if rule.DisableIcmp && (proto == header.ICMPv4ProtocolNumber || proto == header.ICMPv6ProtocolNumber) {
+		    // ICMP is disabled for this subnet
+			return nil
+		}
+
 		// Both IPs match - now check port restrictions
 		// If no port ranges specified, all ports are allowed
 		if len(rule.PortRanges) == 0 {
@@ -180,23 +187,27 @@ type ProxyHandler struct {
 	proxyNotifyHandle *channel.NotificationHandle
 	tcpHandler        *TCPHandler
 	udpHandler        *UDPHandler
+	icmpHandler       *ICMPHandler
 	subnetLookup      *SubnetLookup
 	natTable          map[connKey]*natState
 	destRewriteTable  map[destKey]netip.Addr // Maps original dest to rewritten dest for handler lookups
 	natMu             sync.RWMutex
 	enabled           bool
+	icmpReplies       chan []byte          // Channel for ICMP reply packets to be sent back through the tunnel
+	notifiable        channel.Notification // Notification handler for triggering reads
 }
 
 // ProxyHandlerOptions configures the proxy handler
 type ProxyHandlerOptions struct {
-	EnableTCP bool
-	EnableUDP bool
-	MTU       int
+	EnableTCP  bool
+	EnableUDP  bool
+	EnableICMP bool
+	MTU        int
 }
 
 // NewProxyHandler creates a new proxy handler for promiscuous mode
 func NewProxyHandler(options ProxyHandlerOptions) (*ProxyHandler, error) {
-	if !options.EnableTCP && !options.EnableUDP {
+	if !options.EnableTCP && !options.EnableUDP && !options.EnableICMP {
 		return nil, nil // No proxy needed
 	}
 
@@ -205,6 +216,7 @@ func NewProxyHandler(options ProxyHandlerOptions) (*ProxyHandler, error) {
 		subnetLookup:     NewSubnetLookup(),
 		natTable:         make(map[connKey]*natState),
 		destRewriteTable: make(map[destKey]netip.Addr),
+		icmpReplies:      make(chan []byte, 256), // Buffer for ICMP reply packets
 		proxyEp:          channel.New(1024, uint32(options.MTU), ""),
 		proxyStack: stack.New(stack.Options{
 			NetworkProtocols: []stack.NetworkProtocolFactory{
@@ -236,6 +248,15 @@ func NewProxyHandler(options ProxyHandlerOptions) (*ProxyHandler, error) {
 		}
 	}
 
+	// Initialize ICMP handler if enabled
+	if options.EnableICMP {
+		handler.icmpHandler = NewICMPHandler(handler.proxyStack, handler)
+		if err := handler.icmpHandler.InstallICMPHandler(); err != nil {
+			return nil, fmt.Errorf("failed to install ICMP handler: %v", err)
+		}
+		logger.Info("ProxyHandler: ICMP handler enabled")
+	}
+
 	// // Example 1: Add a rule with no port restrictions (all ports allowed)
 	// // This accepts all traffic FROM 10.0.0.0/24 TO 10.20.20.0/24
 	// sourceSubnet := netip.MustParsePrefix("10.0.0.0/24")
@@ -260,11 +281,11 @@ func NewProxyHandler(options ProxyHandlerOptions) (*ProxyHandler, error) {
 // destPrefix: The IP prefix of the destination
 // rewriteTo: Optional address to rewrite destination to - can be IP/CIDR or domain name
 // If portRanges is nil or empty, all ports are allowed for this subnet
-func (p *ProxyHandler) AddSubnetRule(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange) {
+func (p *ProxyHandler) AddSubnetRule(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange, disableIcmp bool) {
 	if p == nil || !p.enabled {
 		return
 	}
-	p.subnetLookup.AddSubnet(sourcePrefix, destPrefix, rewriteTo, portRanges)
+	p.subnetLookup.AddSubnet(sourcePrefix, destPrefix, rewriteTo, portRanges, disableIcmp)
 }
 
 // RemoveSubnetRule removes a subnet from the proxy handler
@@ -343,6 +364,9 @@ func (p *ProxyHandler) Initialize(notifiable channel.Notification) error {
 		return nil
 	}
 
+	// Store notifiable for triggering notifications on ICMP replies
+	p.notifiable = notifiable
+
 	// Add notification handler
 	p.proxyNotifyHandle = p.proxyEp.AddNotify(notifiable)
 
@@ -421,14 +445,21 @@ func (p *ProxyHandler) HandleIncomingPacket(packet []byte) bool {
 		}
 		udpHeader := header.UDP(packet[headerLen:])
 		dstPort = udpHeader.DestinationPort()
-	default:
-		// For other protocols (ICMP, etc.), use port 0 (must match rules with no port restrictions)
+	case header.ICMPv4ProtocolNumber:
+		// ICMP doesn't have ports, use port 0 (must match rules with no port restrictions)
 		dstPort = 0
+		logger.Debug("HandleIncomingPacket: ICMP packet from %s to %s", srcAddr, dstAddr)
+	default:
+		// For other protocols, use port 0 (must match rules with no port restrictions)
+		dstPort = 0
+		logger.Debug("HandleIncomingPacket: Unknown protocol %d from %s to %s", protocol, srcAddr, dstAddr)
 	}
 
 	// Check if the source IP, destination IP, port, and protocol match any subnet rule
 	matchedRule := p.subnetLookup.Match(srcAddr, dstAddr, dstPort, protocol)
 	if matchedRule != nil {
+		logger.Debug("HandleIncomingPacket: Matched rule for %s -> %s (proto=%d, port=%d)",
+			srcAddr, dstAddr, protocol, dstPort)
 		// Check if we need to perform DNAT
 		if matchedRule.RewriteTo != "" {
 			// Create connection tracking key using original destination
@@ -515,9 +546,12 @@ func (p *ProxyHandler) HandleIncomingPacket(packet []byte) bool {
 			Payload: buffer.MakeWithData(packet),
 		})
 		p.proxyEp.InjectInbound(header.IPv4ProtocolNumber, pkb)
+		logger.Debug("HandleIncomingPacket: Injected packet into proxy stack (proto=%d)", protocol)
 		return true
 	}
 
+	logger.Debug("HandleIncomingPacket: No matching rule for %s -> %s (proto=%d, port=%d)",
+		srcAddr, dstAddr, protocol, dstPort)
 	return false
 }
 
@@ -640,6 +674,15 @@ func (p *ProxyHandler) ReadOutgoingPacket() *buffer.View {
 		return nil
 	}
 
+	// First check for ICMP reply packets (non-blocking)
+	select {
+	case icmpReply := <-p.icmpReplies:
+		logger.Debug("ReadOutgoingPacket: Returning ICMP reply packet (%d bytes)", len(icmpReply))
+		return buffer.NewViewWithData(icmpReply)
+	default:
+		// No ICMP reply available, continue to check proxy endpoint
+	}
+
 	pkt := p.proxyEp.Read()
 	if pkt != nil {
 		view := pkt.ToView()
@@ -669,6 +712,11 @@ func (p *ProxyHandler) ReadOutgoingPacket() *buffer.View {
 					srcPort = udpHeader.SourcePort()
 					dstPort = udpHeader.DestinationPort()
 				}
+			case header.ICMPv4ProtocolNumber:
+				// ICMP packets don't need NAT translation in our implementation
+				// since we construct reply packets with the correct addresses
+				logger.Debug("ReadOutgoingPacket: ICMP packet from %s to %s", srcIP, dstIP)
+				return view
 			}
 
 			// Look up NAT state for reverse translation
@@ -702,12 +750,37 @@ func (p *ProxyHandler) ReadOutgoingPacket() *buffer.View {
 	return nil
 }
 
+// QueueICMPReply queues an ICMP reply packet to be sent back through the tunnel
+func (p *ProxyHandler) QueueICMPReply(packet []byte) bool {
+	if p == nil || !p.enabled {
+		return false
+	}
+
+	select {
+	case p.icmpReplies <- packet:
+		logger.Debug("QueueICMPReply: Queued ICMP reply packet (%d bytes)", len(packet))
+		// Trigger notification so WriteNotify picks up the packet
+		if p.notifiable != nil {
+			p.notifiable.WriteNotify()
+		}
+		return true
+	default:
+		logger.Info("QueueICMPReply: ICMP reply channel full, dropping packet")
+		return false
+	}
+}
+
 // Close cleans up the proxy handler resources
 func (p *ProxyHandler) Close() error {
 	if p == nil || !p.enabled {
 		return nil
 	}
 
+	// Close ICMP replies channel
+	if p.icmpReplies != nil {
+		close(p.icmpReplies)
+	}
+
 	if p.proxyStack != nil {
 		p.proxyStack.RemoveNIC(1)
 		p.proxyStack.Close()

netstack2/tun.go

@@ -56,15 +56,17 @@ type Net netTun
 
 // NetTunOptions contains options for creating a NetTUN device
 type NetTunOptions struct {
-	EnableTCPProxy bool
-	EnableUDPProxy bool
+	EnableTCPProxy  bool
+	EnableUDPProxy  bool
+	EnableICMPProxy bool
 }
 
 // CreateNetTUN creates a new TUN device with netstack without proxying
 func CreateNetTUN(localAddresses, dnsServers []netip.Addr, mtu int) (tun.Device, *Net, error) {
 	return CreateNetTUNWithOptions(localAddresses, dnsServers, mtu, NetTunOptions{
-		EnableTCPProxy: true,
-		EnableUDPProxy: true,
+		EnableTCPProxy:  true,
+		EnableUDPProxy:  true,
+		EnableICMPProxy: true,
 	})
 }
 
@@ -84,13 +86,14 @@ func CreateNetTUNWithOptions(localAddresses, dnsServers []netip.Addr, mtu int, o
 		mtu:            mtu,
 	}
 
-	// Initialize proxy handler if TCP or UDP proxying is enabled
-	if options.EnableTCPProxy || options.EnableUDPProxy {
+	// Initialize proxy handler if TCP, UDP, or ICMP proxying is enabled
+	if options.EnableTCPProxy || options.EnableUDPProxy || options.EnableICMPProxy {
 		var err error
 		dev.proxyHandler, err = NewProxyHandler(ProxyHandlerOptions{
-			EnableTCP: options.EnableTCPProxy,
-			EnableUDP: options.EnableUDPProxy,
-			MTU:       mtu,
+			EnableTCP:  options.EnableTCPProxy,
+			EnableUDP:  options.EnableUDPProxy,
+			EnableICMP: options.EnableICMPProxy,
+			MTU:        mtu,
 		})
 		if err != nil {
 			return nil, nil, fmt.Errorf("failed to create proxy handler: %v", err)
@@ -351,10 +354,10 @@ func (net *Net) ListenUDP(laddr *net.UDPAddr) (*gonet.UDPConn, error) {
 // AddProxySubnetRule adds a subnet rule to the proxy handler
 // If portRanges is nil or empty, all ports are allowed for this subnet
 // rewriteTo can be either an IP/CIDR (e.g., "192.168.1.1/32") or a domain name (e.g., "example.com")
-func (net *Net) AddProxySubnetRule(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange) {
+func (net *Net) AddProxySubnetRule(sourcePrefix, destPrefix netip.Prefix, rewriteTo string, portRanges []PortRange, disableIcmp bool) {
 	tun := (*netTun)(net)
 	if tun.proxyHandler != nil {
-		tun.proxyHandler.AddSubnetRule(sourcePrefix, destPrefix, rewriteTo, portRanges)
+		tun.proxyHandler.AddSubnetRule(sourcePrefix, destPrefix, rewriteTo, portRanges, disableIcmp)
 	}
 }