Handle ICMP not permitted errors

internal/pmtud/errors.go

@@ -5,10 +5,12 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"strings"
 	"time"
 )
 
 var (
+	ErrICMPNotPermitted                            = errors.New("ICMP not permitted")
 	ErrICMPDestinationUnreachable                  = errors.New("ICMP destination unreachable")
 	ErrICMPCommunicationAdministrativelyProhibited = errors.New("communication administratively prohibited")
 	ErrICMPBodyUnsupported                         = errors.New("ICMP body type is not supported")
@@ -16,6 +18,8 @@ var (
 
 func wrapConnErr(err error, timedCtx context.Context, pingTimeout time.Duration) error { //nolint:revive
 	switch {
+	case strings.HasSuffix(err.Error(), "sendto: operation not permitted"):
+		err = fmt.Errorf("%w", ErrICMPNotPermitted)
 	case errors.Is(timedCtx.Err(), context.DeadlineExceeded):
 		err = fmt.Errorf("%w (timed out after %s)", net.ErrClosed, pingTimeout)
 	case timedCtx.Err() != nil:

internal/pmtud/ipv4.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"net/netip"
 	"runtime"
+	"strings"
 	"syscall"
 	"time"
 
@@ -36,6 +37,9 @@ func listenICMPv4(ctx context.Context) (conn net.PacketConn, err error) {
 	const listenAddress = ""
 	packetConn, err := listenConfig.ListenPacket(ctx, "ip4:icmp", listenAddress)
 	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
 		return nil, fmt.Errorf("listening for ICMP packets: %w", err)
 	}
 

internal/pmtud/ipv6.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/netip"
+	"strings"
 	"time"
 
 	"golang.org/x/net/icmp"
@@ -21,6 +22,9 @@ func listenICMPv6(ctx context.Context) (conn net.PacketConn, err error) {
 	const listenAddress = ""
 	packetConn, err := listenConfig.ListenPacket(ctx, "ip6:ipv6-icmp", listenAddress)
 	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
 		return nil, fmt.Errorf("listening for ICMPv6 packets: %w", err)
 	}
 	return packetConn, nil

internal/pmtud/pmtud.go

@@ -7,6 +7,7 @@ import (
 	"math"
 	"net"
 	"net/netip"
+	"strings"
 	"time"
 
 	"golang.org/x/net/icmp"
@@ -87,6 +88,9 @@ func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
 		conn, err = listenICMPv6(ctx)
 	}
 	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
 		return 0, fmt.Errorf("listening for ICMP packets: %w", err)
 	}
 
@@ -120,6 +124,9 @@ func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
 
 		_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice()})
 		if err != nil {
+			if strings.HasSuffix(err.Error(), "sendto: operation not permitted") {
+				err = fmt.Errorf("%w", ErrICMPNotPermitted)
+			}
 			return 0, fmt.Errorf("writing ICMP message: %w", err)
 		}
 	}

internal/vpn/tunnelup.go

@@ -120,10 +120,10 @@ func updateToMaxMTU(ctx context.Context, vpnInterface string,
 	vpnLinkMTU, err = pmtud.PathMTUDiscover(ctx, vpnGatewayIP, vpnLinkMTU, pingTimeout, logger)
 	switch {
 	case err == nil:
-		logger.Infof("Setting VPN interface %s MTU to maximum valid MTU %d", vpnInterface, vpnLinkMTU)
+		logger.Infof("setting VPN interface %s MTU to maximum valid MTU %d", vpnInterface, vpnLinkMTU)
-	case errors.Is(err, pmtud.ErrMTUNotFound):
+	case errors.Is(err, pmtud.ErrMTUNotFound) || errors.Is(err, pmtud.ErrICMPNotPermitted):
 		vpnLinkMTU = int(originalMTU)
-		logger.Infof("Reverting VPN interface %s MTU to %d (due to: %s)",
+		logger.Infof("reverting VPN interface %s MTU to %d (due to: %s)",
 			vpnInterface, originalMTU, err)
 	default:
 		return fmt.Errorf("path MTU discovering: %w", err)