pkg/hostagent: Fix detecting host IPs on the same subnet as the guest

Signed-off-by: Norio Nomura <norio.nomura@gmail.com>

Author: norio-nomura

pkg/hostagent/hostagent.go

@@ -89,6 +89,9 @@ type HostAgent struct {
 	guestIPv4 net.IP
 	guestIPv6 net.IP
 	guestIPMu sync.RWMutex
+
+	// Host interface name on the same subnet as the guest,
+	hostIfnameOnSameSubnetAsGuest string
 	// Host IP address on the same subnet as the guest.
 	hostIPv4 net.IP
 	hostIPv6 net.IP

pkg/hostagent/requirements.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/netip"
 	"runtime"
 	"strings"
 	"time"
@@ -321,36 +322,19 @@ func (a *HostAgent) detectGuestIfnameOnSameSubnetAtHost(stdout string) error {
 	if err != nil {
 		return fmt.Errorf("failed to get network interfaces: %w", err)
 	}
-	var (
-		guestIfnameOnSameSubnetAsHost string
-		hostIPv4                      net.IP
-		hostIPv6                      net.IP
-	)
 	for _, neighbor := range neighbors {
 		for _, ifi := range interfaces {
 			if ifi.HardwareAddr.String() != neighbor.LLADDR {
 				continue
 			}
-			guestIfnameOnSameSubnetAsHost = neighbor.DEV
-			if hostIP := net.ParseIP(neighbor.DST); hostIP.To4() != nil {
-				hostIPv4 = hostIP
-			} else if hostIP.To16() != nil {
-				hostIPv6 = hostIP
-			}
+			a.guestIPMu.Lock()
+			a.guestIfnameOnSameSubnetAsHost = neighbor.DEV
+			a.hostIfnameOnSameSubnetAsGuest = ifi.Name
+			a.guestIPMu.Unlock()
+			logrus.Infof("Detected guest interface %q and host interface %q on the same subnet", neighbor.DEV, ifi.Name)
+			return nil
 		}
 	}
-	a.guestIPMu.Lock()
-	a.guestIfnameOnSameSubnetAsHost = guestIfnameOnSameSubnetAsHost
-	a.hostIPv4 = hostIPv4
-	a.hostIPv6 = hostIPv6
-	a.guestIPMu.Unlock()
-	logrus.Infof("Detected the guest has interface %q in same subnet on the host", guestIfnameOnSameSubnetAsHost)
-	if hostIPv4 != nil {
-		logrus.Infof("The host IPv4 address on the same subnet as the guest is %q", hostIPv4)
-	}
-	if hostIPv6 != nil {
-		logrus.Infof("The host IPv6 address on the same subnet as the guest is %q", hostIPv6)
-	}
 	return nil
 }
 
@@ -359,6 +343,7 @@ func (a *HostAgent) detectGuestIfnameOnSameSubnetAtHost(stdout string) error {
 func (a *HostAgent) detectGuestIPAddress(stdout string) error {
 	a.guestIPMu.RLock()
 	guestIfnameOnSameSubnetAsHost := a.guestIfnameOnSameSubnetAsHost
+	hostIfnameOnSameSubnetAsGuest := a.hostIfnameOnSameSubnetAsGuest
 	a.guestIPMu.RUnlock()
 	if guestIfnameOnSameSubnetAsHost == "" {
 		return nil
@@ -375,37 +360,82 @@ func (a *HostAgent) detectGuestIPAddress(stdout string) error {
 		return fmt.Errorf("failed to parse ip addr output %q: %w", stdout, err)
 	}
 	var (
-		guestIPv4 net.IP
-		guestIPv6 net.IP
+		guestIPv4 netip.Addr
+		guestIPv6 netip.Addr
+		hostIPv4  netip.Addr
+		hostIPv6  netip.Addr
 	)
 	for _, addr := range addrs {
 		if addr.IFNAME == guestIfnameOnSameSubnetAsHost {
 			for _, addr := range addr.ADDRS {
 				if addr.Scope != "global" {
 					continue
 				}
+				var err error
 				switch addr.Family {
 				case "inet":
-					guestIPv4 = net.ParseIP(addr.Local)
+					guestIPv4, err = netip.ParseAddr(addr.Local)
+					if err != nil {
+						logrus.Warnf("failed to parse guest IPv4 address %q: %v", addr.Local, err)
+					}
+					if guestIPv4.Is4In6() {
+						guestIPv4 = guestIPv4.Unmap()
+					}
 				case "inet6":
-					guestIPv6 = net.ParseIP(addr.Local)
+					guestIPv6, err = netip.ParseAddr(addr.Local)
+					if err != nil {
+						logrus.Warnf("failed to parse guest IPv6 address %q: %v", addr.Local, err)
+					}
 				}
 			}
 		}
 	}
-	if guestIPv4 == nil && guestIPv6 == nil {
+	if !guestIPv4.IsValid() && !guestIPv6.IsValid() {
 		logrus.Infof("The interface %q has neither an IPv4 nor an IPv6 address", guestIfnameOnSameSubnetAsHost)
 		return nil
 	}
-	if guestIPv4 != nil {
+	if guestIPv4.IsValid() {
 		logrus.Infof("The guest IPv4 address on the interface %q is %q", guestIfnameOnSameSubnetAsHost, guestIPv4)
 	}
-	if guestIPv6 != nil {
+	if guestIPv6.IsValid() {
 		logrus.Infof("The guest IPv6 address on the interface %q is %q", guestIfnameOnSameSubnetAsHost, guestIPv6)
 	}
+	if hostIfnameOnSameSubnetAsGuest != "" {
+		ifi, err := net.InterfaceByName(hostIfnameOnSameSubnetAsGuest)
+		if err != nil {
+			logrus.Warnf("failed to get the interface %q: %v", hostIfnameOnSameSubnetAsGuest, err)
+		} else if addrs, err := ifi.Addrs(); err != nil {
+			logrus.Warnf("failed to get addresses of the interface %q: %v", hostIfnameOnSameSubnetAsGuest, err)
+		} else {
+			for _, addr := range addrs {
+				if ipnet := addr.(*net.IPNet); ipnet == nil {
+					continue
+				} else if prefix, err := netip.ParsePrefix(ipnet.String()); err != nil {
+					logrus.Warnf("failed to parse the address %q: %v", ipnet.String(), err)
+				} else if prefix.Addr().Is4() {
+					if !hostIPv4.IsValid() && prefix.Contains(guestIPv4) {
+						hostIPv4 = prefix.Addr()
+						logrus.Infof("The host IPv4 address on the same subnet as the guest is %q", hostIPv4)
+					}
+				} else if prefix.Addr().Is4In6() {
+					if !hostIPv4.IsValid() && prefix.Contains(netip.AddrFrom16(guestIPv4.As16())) {
+						hostIPv4 = prefix.Addr().Unmap()
+						logrus.Infof("The host IPv4 address on the same subnet as the guest is %q", hostIPv4)
+					}
+				} else if prefix.Addr().Is6() {
+					if !hostIPv6.IsValid() && prefix.Contains(guestIPv6) {
+						hostIPv6 = prefix.Addr()
+						logrus.Infof("The host IPv6 address on the same subnet as the guest is %q", hostIPv6)
+					}
+				}
+			}
+		}
+	}
 	a.guestIPMu.Lock()
-	a.guestIPv4 = guestIPv4
-	a.guestIPv6 = guestIPv6
+	a.guestIPv4 = net.IP(guestIPv4.AsSlice())
+	a.guestIPv6 = net.IP(guestIPv6.AsSlice())
+	a.hostIPv4 = net.IP(hostIPv4.AsSlice())
+	a.hostIPv6 = net.IP(hostIPv6.AsSlice())
 	a.guestIPMu.Unlock()
 	ctx := context.Background()
 	a.emitGuestIPEvent(ctx, a.GuestIP().String())