fix(kubevip): reject out-of-range routing protocol values

Netlink carries the address and route protocol in a single byte, so a
configured value above 255 was silently truncated on the wire and never
matched again on readback. Reject it during config validation instead.

Signed-off-by: Marcel Fest <marcel.fest@telekom.de>

pkg/kubevip/config_validation.go

@@ -2,6 +2,7 @@ package kubevip
 
 import (
 	"fmt"
+	"math"
 	"net/url"
 	"strings"
 )
@@ -24,10 +25,23 @@ func (c *Config) Validate() error {
 	if err := validateInstanceName(c.InstanceName); err != nil {
 		return err
 	}
+	if err := validateRoutingProtocol(c.RoutingProtocol); err != nil {
+		return err
+	}
 
 	return nil
 }
 
+// validateRoutingProtocol rejects values the kernel cannot represent: netlink
+// carries the address and route protocol in a single byte, so a larger value is
+// silently truncated on the wire and never matches on readback.
+func validateRoutingProtocol(protocol int) error {
+	if protocol < 0 || protocol > math.MaxUint8 {
+		return fmt.Errorf("routingProtocol %d is out of range, must be between 0 and %d", protocol, math.MaxUint8)
+	}
+	return nil
+}
+
 func validateInstanceName(name string) error {
 	if name == "" {
 		return nil

pkg/kubevip/config_validation_test.go

@@ -62,6 +62,30 @@ func TestValidate_InstanceName(t *testing.T) {
 	}
 }
 
+func TestValidate_RoutingProtocol(t *testing.T) {
+	tests := []struct {
+		name     string
+		protocol int
+		wantErr  bool
+	}{
+		{name: "unset", protocol: 0, wantErr: false},
+		{name: "kube-vip default", protocol: 248, wantErr: false},
+		{name: "maximum byte value", protocol: 255, wantErr: false},
+		{name: "truncated on the wire", protocol: 256, wantErr: true},
+		{name: "negative", protocol: -1, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			config := &Config{RoutingProtocol: tt.protocol}
+			err := config.Validate()
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("Validate() error = %v, wantErr %t", err, tt.wantErr)
+			}
+		})
+	}
+}
+
 func TestInstanceNameLimitReservesNftablesPrefixAndFamilySuffix(t *testing.T) {
 	name := strings.Repeat("a", instanceNameMaxLength)
 	if got := len(egressNftablesTablePrefix + name + egressNftablesTableSuffix); got != nftablesNameMaxLength {